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Artificial light at night suppresses the expression of SERCA2 in the left ventricle of the heart in normotensive and hypertensive rats
Experimental Physiology
Abstract
New findings:
What is the central question of this study? Artificial light at night decreases blood pressure and heart rate in rats. Are mentioned changes in heart rate accompanied by changes in protein expression in the heart's left ventricle? What is the main finding and its importance? For the first time, we reported that five weeks of artificial light at night affected protein expression in the heart's left ventricle in normotensive and hypertensive rats. Artificial light at night decreased expression of the sarco/endoplasmic reticulum Ca2+ -ATPase, angiotensin II receptor type 1, and endothelin-1.
Abstract:
Artificial light at night (ALAN) affects the circadian rhythm of the heart rate in normotensive Wistar (WT) and spontaneously hypertensive rats (SHR) through the autonomic nervous system, which regulates the heart's activity through calcium handling, an important regulator in heart contractility. We analysed the expression of the sarco/endoplasmic reticulum Ca2+ -ATPase (SERCA2) and other selected regulatory proteins involved in the regulation of heart contractility, angiotensin II receptor type 1 (AT1 R), endothelin-1 (ET-1) and tyrosine hydroxylase (TH) in the left ventricle of the heart in WT and SHR after two and five weeks of ALAN with intensity 1-2 lx. Expression of SERCA2 was decreased in WT (control: 0.53 ± 0.07; ALAN: 0.46 ± 0.10) and SHR (control: 0.72 ± 0.18; ALAN: 0.56 ± 0.21) after five weeks of ALAN (p = 0.067). Expression of AT1 R was significantly decreased in WT (control: 0.51 ± 0.27; ALAN: 0.34 ± 0.20) and SHR (control: 0.38 ± 0.07; ALAN: 0.23 ± 0.09) after two weeks of ALAN (p = 0.028) and in SHR after five weeks of ALAN. Expression of ET-1 was decreased in WT (control: 0.51 ± 0.27; ALAN: 0.28 ± 0.12) and SHR (control: 0.54 ± 0.10; ALAN: 0.35 ± 0.23) after five weeks of ALAN (p = 0.015). ALAN did not affect the expression of TH in WT or SHR. In conclusion, ALAN suppressed the expression of SERCA2, AT1 R and ET-1, which are important for the regulation of heart contractility, in a strain-dependent pattern in both WT and SHR. This article is protected by copyright. All rights reserved.
... Thoracic aortas were homogenised with a cocktail of saccharose solution, protease and phosphatase inhibitors as published previously [1,22]. In the extracted supernatant, protein concentrations were measured using a BCA Protein Assay Kit (Thermo Fisher Scientific, Waltham, MA, USA). ...
... The impact of ALAN on blood pressure and heart rate depends on the duration of exposure, with the most pronounced changes manifesting after 2 weeks of ALAN exposure. These effects are likely mediated through the autonomic nervous system, involving transmission from the SCN to the heart and vasculature [1,22]. Although the effects of ALAN on blood pressure and its rhythm are known from previous studies [1,12], the effects of ALAN on the functionality and structure of blood vessels remain unknown or are often limited to a one-time point or in the light phase of the day. ...
... The observed effects depended on the length of ALAN exposure; the most significant effects were observed after 2 weeks of ALAN. Similar results were observed in the case of decreased systolic blood pressure, heart rate and sympathetic nervous activity in normotensive Wistar rats [1,12,22] but with a delay in spontaneously hypertensive rats [2] and rats exposed to prenatal hypoxia, which have naturally increased sympathetic activity [12]. In the present study, we calculated sympathetic and vagal activity from blood pressure variability and aLF, aHF indices and their ratio. ...
Artificial light at night (ALAN) disrupts 24-h variability of blood pressure, but the molecular mechanisms underlying these effects are unknown. Therefore, we analysed the daily variability of pulse pressure, the maximum value of acceleration rate of aortic pressure (dP/dt(max)) measured by telemetry and protein expression in the thoracic aorta of normotensive male rats exposed to ALAN (1-2 lx) for 3 weeks. Daily, 24-h variability of pulse pressure and dP/dt(max) was observed during a regular light/dark regimen with higher values during the dark compared to the light phase of the day. ALAN suppressed 24-h variability and enhanced ultradian (<12-h) periods of pulse pressure and dP/dt(max) in duration-dependent manners. From beat-to-beat blood pressure variability, ALAN decreased low-frequency bands (a sympathetic marker) and had minimal effects on high-frequency bands. At the molecular level, ALAN decreased angiotensin II receptor type 1 expression and reduced 24-h variability. ALAN caused the appearance of 12-h oscillations in transforming growth factor β1 and fibulin 4. Expression of sarco/endoplasmic reticulum Ca2+-ATPase type 2 was increased in the middle of the light and dark phase of the day, and ALAN did not affect its daily and 12-h variability. In conclusion, ALAN suppressed 24-h variability of pulse pressure and dP/dt(max), decreased the power of low-frequency bands and differentially affected the expression of specific proteins in the rat thoracic aorta. Suppressed 24-h oscillations by ALAN underline the pulsatility of individual endocrine axes with different periods, disrupting the cardiovascular control of central blood pressure.
... On the other hand, other physiological processes, including cardiovascular regulation, differ significantly depending on whether the organism is diurnal or nocturnal [2,40,81]. The autonomic nervous system, characterised by a pronounced circadian rhythm, directly influences the heart and blood vessels. ...
... In mice and rats, ALAN after four (5 lx) and five weeks (1-2 lx) did not affect heart weight, respectively [25,81]. However, in normotensive and hypertensive male rats, shortterm exposure to ALAN (1-2 lx; 2 weeks) resulted in a significantly decreased expression of angiotensin II receptor type 1 in the heart [81] and an increased expression of eNOS in the thoracic aorta, whereas the vascular expression of endothelin-1 remained unchanged [55]. ...
... In mice and rats, ALAN after four (5 lx) and five weeks (1-2 lx) did not affect heart weight, respectively [25,81]. However, in normotensive and hypertensive male rats, shortterm exposure to ALAN (1-2 lx; 2 weeks) resulted in a significantly decreased expression of angiotensin II receptor type 1 in the heart [81] and an increased expression of eNOS in the thoracic aorta, whereas the vascular expression of endothelin-1 remained unchanged [55]. Prolonged exposure to ALAN (1-2 lx; 5 weeks) resulted in the decreased cardiac expression of the sarco/endoplasmic reticulum Ca 2+ -ATPase and endothelin-1 [81]. ...
Artificial light at night (ALAN) affects most of the population. Through the retinohypothalamic tract, ALAN modulates the activity of the central circadian oscillator and, consequently, various physiological systems, including the cardiovascular one. We summarised the current knowledge about the effects of ALAN on the cardiovascular system in diurnal and nocturnal animals. Based on published data, ALAN reduces the day-night variability of the blood pressure and heart rate in diurnal and nocturnal animals by increasing the nocturnal values of cardiovascular variables in diurnal animals and decreasing them in nocturnal animals. The effects of ALAN on the cardiovascular system are mainly transmitted through the autonomic nervous system. ALAN is also considered a stress-inducing factor, as glucocorticoid and glucose level changes indicate. Moreover, in nocturnal rats, ALAN increases the pressure response to load. In addition, ALAN induces molecular changes in the heart and blood vessels. Changes in the cardiovascular system significantly depend on the duration of ALAN exposure. To some extent, alterations in physical activity can explain the changes observed in the cardiovascular system after ALAN exposure. Although ALAN acts differently on nocturnal and diurnal animals, we can conclude that both exhibit a weakened circadian coordination among physiological systems, which increases the risk of future cardiovascular complications and reduces the ability to anticipate stress.
Background:
Epidemiological studies show that outdoor artificial light at night (ALAN) is linked to metabolic hazards, but its association with metabolic syndrome (MetS) remains unclear. We aimed to investigate the association of outdoor ALAN with MetS in middle-aged and elderly Chinese.
Methods:
From 2017-2020, we conducted a cross-sectional study in a total of 109,452 participants living in ten cities of eastern China. MetS was defined by fasting blood glucose (FG), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), blood pressure (BP), and waist circumference (WC). In 2021, we followed up 4395 participants without MetS at the baseline. Each participant's five-year average exposure to outdoor ALAN, as well as their exposure to green space type, were measured through matching to their address. Generalized linear models were used to assess the associations of outdoor ALAN with MetS. Stratified analyses were performed by sex, age, region, physical activity, and exposure to green space.
Results:
In the cross-sectional study, compared to the first quantile (Q1) of outdoor ALAN exposure, the odds ratios (ORs) of MetS were 1.156 [95 % confidence interval (CI): 1.111-1.203] and 1.073 (95 %CI: 1.021-1.128) respectively in the third and fourth quantiles (Q3, Q4) of outdoor ALAN exposure. The follow-up study found that, compared to the first quantile (Q1) of outdoor ALAN exposure, the OR of MetS in Q4 of ALAN exposure was 1.204 (95 %CI: 1.019-1.422). Adverse associations of ALAN with MetS components, including high FG, high TG, and obesity, were also found. Greater associations of ALAN with MetS were found in males, the elderly, urban residents, those with low frequency of physical activity, and those living in areas with low levels of grass cover and tree cover.
Conclusions:
Outdoor ALAN exposure is associated with an increased MetS risk, especially in males, the elderly, urban residents, those lacking physical activity, and those living in lower levels of grass cover and tree cover.
Growing evidence has shown that Artificial light at night (ALAN) is one of the threatening risk factors which disrupt circadian homeodynamics of cellular processes. The chronobiological role of melatonin seems to represent an important aspect of its contribution to healthy aging. In the present study, we examined the age dependent effect of melatonin on erythrocyte membrane transporters and oxidative stress biomarkers against ALAN to understand the degree of photo-oxidative damage in chronodisrupted rat model. Young (3 months) and old (24 months) male Wistar rats were subdivided in the following four young groups (n = 4) ; (i) control (ii) melatonin (10 mg/kg) (iii) ALAN (500 lux) (iv) ALAN (500 lux) + melatonin (10 mg/kg) and four old groups (n = 4) ; (v) control (vi) melatonin (10 mg/kg) (vii) ALAN (500 lux) (viii) ALAN (500 lux) + melatonin (10 mg/kg) to the experimental conditions for 10 days. Our findings demonstrated that ALAN significantly enhanced erythrocyte membrane lipid hydroperoxides (LHPs), protein carbonyl (PCO) while reduced total thiol (T-SH), and sialic acid (SA) level with higher amplitude in old ALAN group is restored by exogenous supplementation of melatonin. Activity of membrane transporters, sodium potassium ATPase (NKA) and plasma membrane calcium ion ATPase (PMCA) is significantly reduced meanwhile sodium hydrogen exchanger (NHE) activity is enhanced under the influence of ALAN with higher extent in old groups is effectively ameliorated by melatonin treatment. Further melatonin reduced osmotic fragility of erythrocyte in both young and old rats. It has been concluded from results that ALAN provoked redox insult and disrupt transporters activity more prominently in erythrocyte membrane of aged groups. Exogenous supplementation of melatonin is one of the possible therapeutic approaches to reinforce circadian modulations against ALAN in aged populations.
Artificial light is transforming the nighttime environment and quickly becoming one of the most pervasive pollutants on earth. Across taxa, light entrains endogenous circadian clocks that function to synchronize behavioral and physiological rhythms with natural photoperiod. Artificial light at night (ALAN) disrupts these photoperiodic cues and has consequences for humans and wildlife including sleep disruption, physiological stress and increased risk of cardiovascular disease. However, the mechanisms underlying organismal responses to dim ALAN, resembling light pollution, remain elusive. Light pollution exists in the environment at lower levels (<5 lux) than tested in many laboratory studies that link ALAN to circadian rhythm disruption. Few studies have linked dim ALAN to both the upstream regulators of circadian rhythms and downstream behavioral and physiological consequences. We exposed zebra finches (Taeniopygia gutatta) to dim ALAN (1.5 lux) and measured circadian expression of five pacemaker genes in central and peripheral tissues, plasma melatonin, locomotor activity, and biomarkers of cardiovascular health. ALAN caused an increase in nighttime activity and, for males, cardiac hypertrophy. Moreover, downstream effects were detectable after just short duration exposure (10 days) and at dim levels that mimic the intensity of environmental light pollution. However, ALAN did not affect circulating melatonin nor oscillations of circadian gene expression in the central clock (brain) or liver. These findings suggest that dim ALAN can alter behavior and physiology without strong shifts in the rhythmic expression of molecular circadian pacemakers. Approaches that focus on ecologically-relevant ALAN and link complex biological pathways are necessary to understand the mechanisms underlying vertebrate responses to light pollution.
Dim light at night (dLAN) has become a pervasive part of the modern world, and growing evidence shows its association with increased health risks. Though this link is attributed to a disturbed circadian clock, the underlying mechanisms that can explain how circadian disruption from dLAN causes negative health effects remain unclear. Here, we exposed rats to a light–dark cycle (12:12 h) with low-intensity light at night (~2 lx) for 2 and 5 weeks and explored the steady-state pattern of circulating immune cells and renal immune-related markers, which are well controlled by the circadian clock. After 5 weeks, dLAN impaired the daily variation in several types of white blood cells, especially monocytes and T cells. Two-week dLAN caused a reduction in blood monocytes and altered gene expression of macrophage marker Cd68 and monocyte-attracting chemokine Ccl2 in the kidney. Interestingly, dLAN decreased renal 3-nitrotyrosine levels and resulted in up-regulation of the main endogenous antioxidant pathways, indicating a disturbance in the renal redox balance and an activation of compensatory mechanisms. These effects paralleled the altered renal expression of the molecular clock components and increased plasma corticosterone levels. Together, our results show that chronic exposure to dLAN weakened the circadian control of daily variation of circulating immune cells and disturbed renal immune and redox homeostasis. Consequences of this dLAN-disturbed immune balance on the ability of the immune system to cope with other challenges should by clarified in further studies.
Exposure to light at inappropriate times in relation to the solar cycle can disturb circadian endocrine and metabolic rhythms. Previous studies have suggested an association between light exposure at night (LAN) and obesity, an important risk factor of atherosclerosis, although it remains unclear whether LAN associates with progression of atherosclerosis. To evaluate the longitudinal association between bedroom LAN intensity and progression of carotid atherosclerosis, light intensity in the bedroom at baseline and carotid artery intima-media thickness (IMT) at baseline and follow-up were measured in 989 elderly participants (945 at baseline and 780 at a median follow-up time of 34 months). The mean age of the participants was 71.4 ± 6.9 years. The average mean and maximal carotid IMT at baseline were 0.88 ± 0.15 and 1.10 ± 0.32 mm, respectively. The median intensity of bedroom LAN was 0.68 lx (IQR, 0.07-3.29). In multivariable analysis adjusted for potential confounders, the highest LAN group exhibited a significant increase in mean carotid IMT (adjusted β, 0.028; 95% CI, 0.005-0.052; P = 0.019) compared with the lowest LAN quartile group. A similar relationship was found between LAN and maximal carotid IMT (adjusted β, 0.083; 95% CI, 0.037-0.129; P < 0.001). In conclusion, we found a clear and significant association between bedroom LAN intensity and progression of subclinical carotid atherosclerosis, which was independent of known risk factors for atherosclerosis, including age, obesity, smoking, economic status, hypertension, and diabetes. Indoor light pollution may be a potential risk factor for atherosclerosis in the general population.
Circadian rhythms are an inherent property of physiological processes and can be disturbed by irregular environmental cycles, including artificial light at night (ALAN). Circadian disruption may contribute to many pathologies, such as hypertension, obesity, and type 2 diabetes, but the underlying mechanisms are not understood. Our study investigated the consequences of ALAN on cardiovascular and metabolic parameters in spontaneously hypertensive rats, which represent an animal model of essential hypertension and insulin resistance. Adult males were exposed to a 12 h light − 12 h dark cycle and the ALAN group experienced dim light at night (1–2 lx), either for 2 or 5 weeks. Rats on ALAN showed a loss of light–dark variability for systolic blood pressure, but not for heart rate. Moreover, a gradual increase of systolic blood pressure was recorded over 5 weeks of ALAN. Exposure to ALAN increased plasma insulin and hepatic triglyceride levels. An increased expression of metabolic transcription factors, Pparα and Pparγ, in the epididymal fat and a decreased expression of Glut4 in the heart was found in the ALAN group. Our results demonstrate that low-intensity ALAN can disturb blood pressure control and augment insulin resistance in spontaneously hypertensive rats, and may represent a serious risk factor for cardiometabolic diseases.
Cardiac arrhythmias are a leading cause of cardiovascular death. It has long been accepted that life-threatening cardiac arrhythmias (ventricular tachycardia, ventricular fibrillation and sudden cardiac death) are more likely to occur in the morning after waking. It is perhaps less well recognised that there is a circadian rhythm in cardiac pacemaking and other electrophysiological properties of the heart. In addition, there is a circadian rhythm in other arrhythmias, for example bradyarrhythmias and supraventricular arrhythmias. Two mechanisms may underlie this: (1) a central circadian clock in the suprachiasmatic nucleus in the hypothalamus may directly affect the electrophysiology of the heart and arrhythmogenesis via various neurohumoral factors, particularly the autonomic nervous system; or (2) a local circadian clock in the heart itself (albeit under the control of the central clock) may drive a circadian rhythm in the expression of ion channels in the heart, which in turn varies arrhythmic substrate. This review summarises the current understanding of the circadian rhythm in cardiac electrophysiology, arrhythmogenesis and the underlying molecular mechanisms.
Shiftwork became common during the last few decades with the growing demands of human life. Despite the social inactivity and irregularity in habits, working in continuous irregular shifts causes serious health issues including sleep disorders, psychiatric disorders, cancer, and metabolic disorders. These health problems arise due to the disruption in circadian clock system, which is associated with alterations in genetic expressions. Alteration in clock controlling genes further affects genes linked with disorders including major depression disorder, bipolar disorder, phase delay and phase advance sleep syndromes, breast cancer, and colon cancer. A diverse research work is needed focusing on broad spectrum changes caused by jet lag in brain and neuronal system. This review is an attempt to motivate the researchers to conduct advanced studies in this area to identify the risk factors and mechanisms. Its goal is extended to make the shift workers aware about the risks associated with shiftwork.
Most organisms use internal biological clocks to match behavioural and physiological processes to specific phases of the day–night cycle. Central to this is the synchronisation of internal processes across multiple organ systems. Environmental desynchrony (e.g. shift work) profoundly impacts human health, increasing cardiovascular disease and diabetes risk, yet the underlying mechanisms remain unclear. Here, we characterise the impact of desynchrony between the internal clock and the external light–dark (LD) cycle on mammalian physiology. We reveal that even under stable LD environments, phase misalignment has a profound effect, with decreased metabolic efficiency and disrupted cardiac function including prolonged QT interval duration. Importantly, physiological dysfunction is not driven by disrupted core clock function, nor by an internal desynchrony between organs, but rather the altered phase relationship between the internal clockwork and the external environment. We suggest phase misalignment as a major driver of pathologies associated with shift work, chronotype and social jetlag.
Salusin-β is a bioactive peptide involved in vascular smooth muscle cell proliferation, vascular fibrosis and hypertension. The present study was designed to determine the effects of silencing salusin-β on hypertension and cardiovascular remodeling in spontaneously hypertensive rats (SHR). Thirteen-week-old male SHR and normotensive Wistar-Kyoto rats (WKY) were subjected to intravenous injection of PBS, adenoviral vectors encoding salusin-β shRNA (Ad-Sal-shRNA) or a scramble shRNA. Salusin-β levels in plasma, myocardium and mesenteric artery were increased in SHR. Silencing salusin-β had no significant effect on blood pressure in WKY, but reduced blood pressure in SHR. It reduced the ratio of left ventricle weight to body weight, cross-sectional areas of cardiocytes and perivascular fibrosis, and decreased the media thickness and the media/lumen ratio of arteries in SHR. Silencing salusin-β almost normalized plasma norepinephrine and angiotensin II levels in SHR. It prevented the upregulation of angiotensin II and AT1 receptors, and reduced the NAD(P)H oxidase activity and superoxide anion levels in myocardium and mesenteric artery of SHR. Knockdown of salusin-β attenuated cell proliferation and fibrosis in vascular smooth muscle cells from SHR. These results indicate that silencing salusin-β attenuates hypertension and cardiovascular remodeling in SHR.
Circadian clocks impact vital cardiac parameters such as blood pressure and heart rate, and adverse cardiac events such as myocardial infarction and sudden cardiac death. In mammals, the central circadian pacemaker, located in the suprachiasmatic nucleus of the hypothalamus, synchronizes cellular circadian clocks in the heart and many other tissues throughout the body. Cardiac ventricle explants maintain autonomous contractions and robust circadian oscillations of clock gene expression in culture. In the present study, we examined the relationship between intrinsic myocardial function and circadian rhythms in cultures from mouse heart. We cultured ventricular explants or dispersed cardiomyocytes from neonatal mice expressing a PER2::LUC bioluminescent reporter of circadian clock gene expression. We found that isoproterenol, a β-adrenoceptor agonist known to increase heart rate and contractility, also amplifies PER2 circadian rhythms in ventricular explants. We found robust, cell-autonomous PER2 circadian rhythms in dispersed cardiomyocytes. Single-cell rhythms were initially synchronized in ventricular explants but desynchronized in dispersed cells. In addition, we developed a method for long-term, simultaneous monitoring of clock gene expression, contraction rate, and basal intracellular Ca2+ level in cardiomyocytes using PER2::LUC in combination with GCaMP3, a genetically encoded fluorescent Ca2+ reporter. In contrast to robust PER2 circadian rhythms in cardiomyocytes, we detected no rhythms in contraction rate and only weak rhythms in basal Ca2+ level. In summary, we found that PER2 circadian rhythms of cardiomyocytes are cell-autonomous, amplified by adrenergic signaling, and synchronized by intercellular communication in ventricle explants, but we detected no robust circadian rhythms in contraction rate or basal Ca2+.
Elevated heart rate is a risk factor for cardiovascular and all-cause mortalities in the general population and various cardiovascular pathologies. Insufficient heart rate decline during the night, that is, nondipping heart rate, also increases cardiovascular risk. Abnormal heart rate reflects an autonomic nervous system imbalance in terms of relative dominance of sympathetic tone. There are only a few prospective studies concerning the effect of heart rate reduction in coronary heart disease and heart failure. In hypertensive patients, retrospective analyses show no additional benefit of slowing down the heart rate by beta-blockade to blood pressure reduction. Melatonin, a secretory product of the pineal gland, has several attributes, which predict melatonin to be a promising candidate in the struggle against elevated heart rate and its consequences in the hypertensive population. First, melatonin production depends on the sympathetic stimulation of the pineal gland. On the other hand, melatonin inhibits the sympathetic system in several ways representing potentially the counter-regulatory mechanism to normalize excessive sympathetic drive. Second, administration of melatonin reduces heart rate in animals and humans. Third, the chronobiological action of melatonin may normalize the insufficient nocturnal decline of heart rate. Moreover, melatonin reduces the development of endothelial dysfunction and atherosclerosis, which are considered a crucial pathophysiological disorder of increased heart rate and pulsatile blood flow. The antihypertensive and antiremodeling action of melatonin along with its beneficial effects on lipid profile and insulin resistance may be of additional benefit. A clinical trial investigating melatonin actions in hypertensive patients with increased heart rate is warranted. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Effects of phase delay shifts (PDS) of light in combination with moderately increased salt intake (SL) (2%) or time restriction of food (FR) during the light-time (passive phase) on heart rate (HR), blood pressure (BP) and locomotor activity (LA) in radiotelemetry-measured rats were evaluated. PDS decreased amplitude and spectral power of circadian oscillations of HR, BP and LA. Moderately increased SL did not interfere with the circadian rhythmicity of HR, BP or LA. A prominent decrease in amplitude and spectral power of circadian oscillations was observed if food was available during the lighttime. Combination of PDS with FR split cardiovascular and behavioural parameters. In conclusion, food availability during the light-time in combination with PDS decreased amplitude and spectral power of circadian oscillations of BP, HR and LA more than PDS only. Different response of cardiovascular and behavioural parameters to photic and non-photic stimuli can have consequences for shift workers.
Renin-angiotensin system activation is a feature of many cardiovascular conditions. Activity of myocardial reduced nicotinamide adenine dinucleotide phosphate oxidase 2 (NADPH oxidase 2 or Nox2) is enhanced by angiotensin II (Ang II) and contributes to increased hypertrophy, fibrosis, and adverse remodeling. Recent studies found that Nox2-mediated reactive oxygen species production modulates physiological cardiomyocyte function.
This study sought to investigate the effects of cardiomyocyte Nox2 on contractile function during increased Ang II activation.
We generated a cardiomyocyte-targeted Nox2-transgenic mouse model and studied the effects of in vivo and ex vivo Ang II stimulation, as well as chronic aortic banding.
Chronic subpressor Ang II infusion induced greater cardiac hypertrophy in transgenic than wild-type mice but unexpectedly enhanced contractile function. Acute Ang II treatment also enhanced contractile function in transgenic hearts in vivo and transgenic cardiomyocytes ex vivo. Ang II-stimulated Nox2 activity increased sarcoplasmic reticulum (SR) Ca(2+) uptake in transgenic mice, increased the Ca(2+) transient and contractile amplitude, and accelerated cardiomyocyte contraction and relaxation. Elevated Nox2 activity increased phospholamban phosphorylation in both hearts and cardiomyocytes, related to inhibition of protein phosphatase 1 activity. In a model of aortic banding-induced chronic pressure overload, heart function was similarly depressed in transgenic and wild-type mice.
We identified a novel mechanism in which Nox2 modulates cardiomyocyte SR Ca(2+) uptake and contractile function through redox-regulated changes in phospholamban phosphorylation. This mechanism can drive increased contractility in the short term in disease states characterized by enhanced renin-angiotensin system activation.
Copyright © 2015 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.
PKA phosphorylates multiple molecules involved in calcium (Ca2+) handling in cardiac myocytes and is considered to be the predominant regulator of β-adrenergic receptor-mediated enhancement of cardiac contractility; however, recent identification of exchange protein activated by cAMP (EPAC), which is independently activated by cAMP, has challenged this paradigm. Mice lacking Epac1 (Epac1 KO) exhibited decreased cardiac contractility with reduced phospholamban (PLN) phosphorylation at serine-16, the major PKA-mediated phosphorylation site. In Epac1 KO mice, intracellular Ca2+ storage and the magnitude of Ca2+ movement were decreased; however, PKA expression remained unchanged, and activation of PKA with isoproterenol improved cardiac contractility. In contrast, direct activation of EPAC in cardiomyocytes led to increased PLN phosphorylation at serine-16, which was dependent on PLC and PKCε. Importantly, Epac1 deletion protected the heart from various stresses, while Epac2 deletion was not protective. Compared with WT mice, aortic banding induced a similar degree of cardiac hypertrophy in Epac1 KO; however, lack of Epac1 prevented subsequent cardiac dysfunction as a result of decreased cardiac myocyte apoptosis and fibrosis. Similarly, Epac1 KO animals showed resistance to isoproterenol- and aging-induced cardiomyopathy and attenuation of arrhythmogenic activity. These data support Epac1 as an important regulator of PKA-independent PLN phosphorylation and indicate that Epac1 regulates cardiac responsiveness to various stresses.
Circadian misalignment between internal and environmental rhythms dysregulates blood pressure (BP) variability because of disruption of the biological clock, resulting in increased nighttime BP. Although exposure to light-at-night is associated with the circadian misalignment, it remains unclear whether exposure to light-at-night in home settings is associated with nighttime BP. In this cross-sectional analysis of 528 elderly individuals (mean age: 72.8 years), we measured bedroom light intensity at 1-min intervals on two consecutive nights along with ambulatory BP, overnight urinary melatonin excretion and actigraphy. With regard to adjusted mean comparisons using analysis of covariance, the light-at-night group (average: ≥5 lux; n = 109) showed significantly higher nighttime systolic BP (SBP; adjusted mean: 120.8 vs. 116.5 mmHg, p = 0.01) and diastolic BP (70.1 vs. 67.1 mmHg, p < 0.01) compared with the Darker group (average: <5 lux; n = 419) independently of potential confounding factors including overnight urinary melatonin excretion and actigraphic sleep quality. We observed consistent associations between light-at-night and nighttime BP in different cutoff values for light-at-night intensity (i.e. 3 and 10 lux). In conclusion, exposure to light-at-night in home settings is significantly associated with increased nighttime BP in elderly individuals independently of overnight urinary melatonin excretion. A 4.3 mmHg increase in nighttime SBP is associated with a 6.1% increase in total mortality, which corresponds to approximately 10 000 annual excess deaths in Japanese elderly population.
Circadian rhythms are approximate 24-h oscillations in physiology and behavior. Circadian rhythm disruption has been associated with increased incidence of hypertension, coronary artery disease, dyslipidemia, and other cardiovascular pathologies in both humans and animal models. Mice lacking the core circadian clock gene, brain and muscle aryl hydrocarbon receptor nuclear translocator (ARNT)-like protein (Bmal1), are behaviorally arrhythmic, die prematurely, and display a wide range of organ pathologies. However, data are lacking on the role of Bmal1 on the structural and functional integrity of cardiac muscle. In the present study, we demonstrate that Bmal1(-/-) mice develop dilated cardiomyopathy with age, characterized by thinning of the myocardial walls, dilation of the left ventricle, and decreased cardiac performance. Shortly after birth the Bmal1(-/-) mice exhibit a transient increase in myocardial weight, followed by regression and later onset of dilation and failure. Ex vivo working heart preparations revealed systolic ventricular dysfunction at the onset of dilation and failure, preceded by downregulation of both myosin heavy chain isoform mRNAs. We observed structural disorganization at the level of the sarcomere with a shift in titin isoform composition toward the stiffer N2B isoform. However, passive tension generation in single cardiomyocytes was not increased. Collectively, these findings suggest that the loss of the circadian clock gene, Bmal1, gives rise to the development of an age-associated dilated cardiomyopathy, which is associated with shifts in titin isoform composition, altered myosin heavy chain gene expression, and disruption of sarcomere structure.
Left ventricular (LV) diastolic dysfunction, particularly relaxation abnormalities, are known to be associated with the development of LV hypertrophy (LVH). Preliminary human and animal studies suggested that early LV diastolic dysfunction may be revealed independently of LVH. However, whether LV diastolic dysfunction is compromised before the onset of hypertension and LVH remains unknown. We therefore evaluated LV diastolic function in spontaneously hypertensive rats (SHR) at different ages and tested whether LV diastolic dysfunction is associated with abnormal intracellular calcium homeostasis. LV systolic and diastolic functions were evaluated by invasive and echocardiographic methods in 3-week-old (without hypertension) and 5-week-old (with hypertension) SHR and Wistar-Kyoto control rats. Basal intracytoplasmic calcium and sarcoplasmic reticulum (SR) Ca(2+) contents were measured in cardiomyocytes using fura-2 AM. Sarco(endo)plasmic Ca(2+)-ATPase isoform 2a (SERCA 2a) and phospholamban (PLB) expressions were quantified by Western blot and quantitative RT-PCR techniques. LV relaxation dysfunction was observed in 3-week-old SHR rats before onset of hypertension and LVH. An increase in basal intracytoplasmic Ca(2+) and a decrease in SR Ca(2+) release were demonstrated in SHR. Decreased expression of SERCA 2a and Ser16 PLB (p16-PLB) protein levels was also observed in SHR rats, whereas mRNA expression was not decreased. For the first time, we have shown that LV myocardial dysfunction precedes hypertension in 3-week-old SHR rats. This LV myocardial dysfunction was associated with high diastolic [Ca(2+)](i) possibly due to decreased SERCA 2a and p16-PLB protein levels. Diastolic dysfunction may be a potential predictive marker of arterial hypertension in genetic hypertension syndromes.
Underlying cardiac pathology and atrial fibrillation (AF) affect the molecular remodeling of ion channels in the atria. Changes in the expression of these molecules have not been demonstrated in Korean patients with mitral valvular heart disease. Thus, the purpose of this study was to analyze ion channel expression in patients with chronic AF and mitral valvular heart disease.
A total of 17 patients (eight males and nine females; mean age, 57 ± 14 years [range, 19 to 77]) undergoing open-heart surgery were included in the study. Twelve patients (seven with coronary artery disease and five with aortic valvular disease) had sinus rhythm, and five patients (all with mitral valvular disease) had chronic, permanent AF. A piece of right atrial appendage tissue (0.5 g) was obtained during surgery. RT-PCR was used to evaluate the expression of L-type Ca(2+) channels, ryanodine receptor (RyR2), sarcoplasmic reticular Ca(2+)-ATPase (SERCA2), gene encoding the rapid component of the delayed rectifier I(kr) (HERG), gene encoding calcium-independent transient outward current I(to1) (Kv4.3), gene encoding the ultrarapid component of the delayed rectifier I(ku) (Kv1.5), K(+) channel-interacting protein 2 (KChIP2), hyperpolarization-activated cation channel 2 associated with the pacemaker current I(f) (HCN2), and gene encoding Na(+) channel (SCN5A).
Reduced L-type Ca(2+) channel, RyR2, SERCA2, Kv1.5, and KChIP2 expression and borderline increased HCN2 expression were observed in the patients with AF and mitral valvular heart disease. Left atrial diameter was negatively correlated with RyR2 and KChIP2 expression. Fractional area shortening of the left atrium was positively correlated with RyR2 and KChIP2 expression.
Alterations in ion channel expression and the anatomical substrate may favor the initiation and maintenance of AF in patients with mitral valvular heart disease.
Malfunction of the circadian clock has been linked to the pathogenesis of a variety of diseases. We show that mice lacking the core clock components Cryptochrome-1 (Cry1) and Cryptochrome-2 (Cry2) (Cry-null mice) show salt-sensitive hypertension due to abnormally high synthesis of the mineralocorticoid aldosterone by the adrenal gland. An extensive search for the underlying cause led us to identify type VI 3beta-hydroxyl-steroid dehydrogenase (Hsd3b6) as a new hypertension risk factor in mice. Hsd3b6 is expressed exclusively in aldosterone-producing cells and is under transcriptional control of the circadian clock. In Cry-null mice, Hsd3b6 messenger RNA and protein levels are constitutively high, leading to a marked increase in 3beta-hydroxysteroid dehydrogenase-isomerase (3beta-HSD) enzymatic activity and, as a consequence, enhanced aldosterone production. These data place Hsd3b6 in a pivotal position through which circadian clock malfunction is coupled to the development of hypertension. Translation of these findings to humans will require clinical examination of human HSD3B1 gene, which we found to be functionally similar to mouse Hsd3b6.
The core molecular clockwork in the suprachiasmatic nucleus (SCN) is based on autoregulatory feedback loops of transcriptional activators (CLOCK/NPAS2 and BMAL1) and inhibitors (mPER1-2 and mCRY1-2). To synchronize the phase of the molecular clockwork to the environmental day and night condition, light at dusk and dawn increases mPer expression. However, the signal transduction pathways differ remarkably between the day/night and the night/day transition. Light during early night leads to intracellular Ca(2+) release by neuronal ryanodine receptors (RyRs), resulting in phase delays. Light during late night triggers an increase in guanylyl cyclase activity, resulting in phase advances. To date, it is still unknown how the core molecular clockwork regulates the availability of the respective input pathway components. Therefore, we examined light resetting mechanisms in mice with an impaired molecular clockwork (BMAL1(-/-)) and the corresponding wild type (BMAL1(+/+)) using in situ hybridization, real-time PCR, immunohistochemistry, and a luciferase reporter system. In addition, intracellular calcium concentrations (Ca(2+)(i)) were measured in SCN slices using two-photon microscopy. In the SCN of BMAL1(-/-) mice Ryr mRNA and RyR protein levels were reduced, and light-induced mPer expression was selectively impaired during early night. Transcription assays with NIH3T3 fibroblasts showed that Ryr expression was activated by CLOCK::BMAL1 and inhibited by mCRY1. The Ca(2+)(i) response of SCN cells to the RyR agonist caffeine was reduced in BMAL1(-/-) compared with BMAL1(+/+) mice. Our findings provide the first evidence that the mammalian molecular clockwork influences Ryr expression and thus controls its own photic input pathway components.
"Physiological" aging as well as early and progressive cardiac hypertrophy may affect action potential (AP) pattern, contractile function, and Ca(2+) handling. We hypothesize that contractile function is disturbed in hypertrophy from early stages and is differently affected in aged myocardium. In vivo function, cardiomyocyte contractile behavior and APs were compared in Wistar-Kyoto (WIS) rats and spontaneously hypertensive rats (SHR) at different ages and degrees of hypertrophy (3-4, 9-11, 20-24 months). Post-rest (PR) behavior was used to investigate the relative contribution of the sarcoplasmic reticulum (SR) and the Na/Ca exchanger (NCX) to cytosolic Ca(2+) removal. APs were recorded by whole-cell current-clamp and sarcomere shortening by video microscopy. Cyclopiazonic acid was used to suppress Ca(2+) ATPase (SERCA) function. Heart weight/body weight ratio was increased in SHR versus WIS within all age groups. Myocyte steady state (SS) shortening amplitude was reduced in young SHR versus WIS. Aging led to a significant decay of SS contractile amplitude and relengthening velocity in WIS, but the PR potentiation was maintained. In contrast, aging in SHR led to a decrease of PR potentiation, while SS contraction and relengthening velocity increased. APD(50%) was always prolonged in SHR versus WIS. With aging, APD(50%) increased in both WIS and SHR, but was still shorter in WIS. However, in old WIS the late AP portion (APD(90%)) was prolonged. Ca(2+) handling and AP properties are disturbed progressively with aging and with increasing hypertrophy. Decreased amplitude of shortening and velocity of relengthening in aged WIS may be attributed to reduced SERCA function. In SHR, an increase in SR leak and shift towards transmembraneous Ca handling via NCX may be responsible for the changes in contractile function. A prolonged APD(90%) in aged WIS may be an adaptive mechanism to preserve basal contractility. Therefore, the effects on contractile parameters and AP are different in hypertrophy and aging.
Prenatal hypoxia (PH) has negative consequences on the cardiovascular system in adulthood and can affect the responses to additional insults later in life. We explored the effects of PH imposed during embryonic day 20 (10.5% O 2 for 12 h) on circadian rhythms of systolic blood pressure (BP) and heart rate (HR) in mature male rat offspring measured by telemetry. We evaluated: (1) stability of BP and HR changes after PH; (2) circadian variability of BP and HR after 2 and 5 weeks of exposure to artificial light at night (ALAN; 1–2 lx); and (3) response of BP and HR to norepinephrine. PH increased BP in the dark (134 ± 2 mmHg vs. control 127 ± 2 mmHg; p = 0.05) and marginally in the light (125 ± 1 mmHg vs. control 120 ± 2 mmHg) phase of the day but not HR. The effect of PH was highly repeatable between 21- and 27-week-old PH male offspring. Two weeks of ALAN decreased the circadian variability of HR ( p < 0.05) and BP more in control than PH rats. After 5 weeks of ALAN, the circadian variability of HR and BP were damped compared to LD and did not differ between control and PH rats ( p < 0.05). Responses of BP and HR to norepinephrine did not differ between control and PH rats. Hypoxia at the end of the embryonic period increases BP and affects the functioning of the cardiovascular system in mature male offspring. ALAN in adulthood decreased the circadian variability of cardiovascular parameters, more in control than PH rats.
Background:
Cardiac gene expression and arrhythmia occurrence have time-of-day variation; however, daily changes in cardiac electrophysiology, arrhythmia susceptibility, and Ca2+ handling have not been characterized. Furthermore, how these patterns change with age is unknown.
Methods:
Hearts were isolated during the light (zeitgeber time [ZT] 4 and ZT9) and dark cycle (ZT14 and ZT21) from adult (12-18 weeks) male mice. Hearts from aged (18-20 months) male mice were isolated at ZT4 and ZT14. All hearts were Langendorff-perfused for optical mapping with voltage- and Ca2+-sensitive dyes (n=4-7/group). Cardiac gene and protein expression were assessed with real-time polymerase chain reaction (n=4-6/group) and Western blot (n=3-4/group).
Results:
Adult hearts had the shortest action potential duration (APD) and Ca2+ transient duration (CaTD) at ZT14 (APD80: ZT4: 45.4±4.1 ms; ZT9: 45.1±8.6 ms; ZT14: 34.7±4.2 ms; ZT21: 49.2±7.6 ms, P<0.05 versus ZT4 and ZT21; and CaTD80: ZT4: 70.1±3.3 ms; ZT9: 72.7±2.7 ms; ZT14: 64.3±3.3 ms; ZT21: 74.4±1.2 ms, P<0.05 versus other time points). The pacing frequency at which CaT alternans emerged was faster, and average CaT alternans magnitude was significantly reduced at ZT14 compared with the other time points. There was a trend for decreased spontaneous premature ventricular complexes and pacing-induced ventricular arrhythmias at ZT14, and the hearts at ZT14 had diminished responses to isoproterenol compared with ZT4 (ZT4: 49.5.0±5.6% versus ZT14: 22.7±9.5% decrease in APD, P<0.01). In contrast, aged hearts exhibited no difference between ZT14 and ZT4 in nearly every parameter assessed (except APD80: ZT4: 39.7±1.9 ms versus ZT14: 33.8±3.1 ms, P<0.01). Gene expression of KCNA5 (potassium voltage-gated channel subfamily A member 5; encoding Kv1.5) was increased, whereas gene expression of ADRB1 (encoding β1-adrenergic receptors) was decreased at ZT14 versus ZT4 in adult hearts. No time-of-day changes in expression or phosphorylation of Ca2+ handling proteins (SERCA2 [sarco/endoplasmic reticulum Ca2+-ATPase], RyR2 [ryanodine receptor 2], and PLB [phospholamban]) was found in ex vivo perfused adult isolated hearts.
Conclusions:
Isolated adult hearts have strong time-of-day variation in cardiac electrophysiology, Ca2+ handling, and adrenergic responsiveness, which is disrupted with age.
Aims:
Cardiovascular parameters exhibit significant 24-h variability, which is coordinated by the suprachiasmatic nucleus (SCN), and light/dark cycles control SCN activity. We aimed to study the effects of light at night (ALAN; 1-2 lx) on cardiovascular system control in normotensive rats.
Main methods:
Heart rate (HR) and blood pressure (BP) were measured by telemetry during five weeks of ALAN exposure. From beat-to-beat telemetry data, we evaluated spontaneous baroreflex sensitivity (sBRS). After 2 (A2) and 5 (A5) weeks of ALAN, plasma melatonin concentrations and the response of BP and HR to norepinephrine administration were measured. The expression of endothelial nitric oxide synthase (eNOS) and endothelin-1 was determined in the aorta. Spontaneous exploratory behaviour was evaluated in an open-field test.
Key findings:
ALAN significantly suppressed the 24-h variability in the HR, BP, and sBRS after A2, although the parameters were partially restored after A5. The daily variability in the BP response to norepinephrine was reduced after A2 and restored after A5. ALAN increased the BP response to norepinephrine compared to the control after A5. Increased eNOS expression was found in arteries after A2 but not A5. Endothelin-1 expression was not affected by ALAN. Plasma melatonin levels were suppressed after A2 and A5. Spontaneous exploratory behaviour was reduced.
Significance:
ALAN decreased plasma melatonin and the 24-h variability in the haemodynamic parameters and increased the BP response to norepinephrine. A low intensity ALAN can suppress circadian control of the cardiovascular system with negative consequences on the anticipation of a load.
This work evaluated the effects of long-term kefir treatment in cardiac function (cardiac contractility and calcium-handling proteins) and the central nervous system (CNS) control of the sympathetic signaling in spontaneously hypertensive rats (SHR). Male normotensive rats [Wistar Kyoto rats (WKYs)] and SHRs were divided into three groups: WKYs and SHRs treated with vehicle, and SHRs treated with milk fermented by the grains of kefir (5%; SHR-Kefir; oral gavage, 0.3 ml/100 g daily/9 weeks). At the end of treatment, mean arterial pressure (MAP) and heart rate (HR) were measured by direct arterial catheterization. Hemodynamic parameters (left ventricular systolic pressure, left ventricular isovolumetric relaxation time constant, maximal and minimal pressure decay) were acquired through a left ventricular catheter implantation. Left ventricle protein expressions of phospholamban (PLB), its phosphorylated form (p-PLB) and sarcoplasmic reticulum Ca ²⁺ -ATPase (SERCA2a) were determined by Western blot. Tyrosine hydroxylase (TH) protein expression was evaluated via immunofluorescence within the paraventricular nucleus (PVN) of the hypothalamus and the rostral ventrolateral medulla (RVLM). SHR-Kefir group presented lower MAP and HR compared to SHRs. Kefir treatment ameliorated cardiac hypertrophy and promoted reduced expression of PLB, p-PLB and SERCA2a contractile proteins. Within the PVN and RVML, TH protein overexpression observed in SHRs was reduced by probiotic treatment. In addition, kefir improved cardiac hemodynamic parameters in SHR-treated animals. Altogether, the data show that long-term kefir treatment reduced blood pressure by mechanisms involving reduction of cardiac hypertrophy, improvement of cardiac contractility and calcium-handling proteins, and reduction in the CNS regulation of the sympathetic activity.
Alterations of sympathoadrenal and sympathoneural systems have been suggested to be involved in the pathogenesis of hypertension in spontaneously hypertensive rats (SHR). To evaluate the ontogenetic changes of these systems, mRNA and protein expressions of catecholaminergic system genes were measured in adrenal glands and sympathetic ganglia, and the catecholamine levels were determined in adrenal glands, sympathetic ganglia and plasma of prehypertensive (4-week-old) and hypertensive (24-week-old) SHR. Vascular sympathetic innervation was visualized in the femoral artery by glyoxylic acid. In the adrenal glands of prehypertensive SHR, the expression of catecholamine biosynthetic enzymes Ddc, Dbh and Pnmt was lower than in aged-matched Wistar-Kyoto rats. In contrast, the adrenal content of dopamine, noradrenaline and adrenaline was higher in prehypertensive SHR (141%, 123% and 120% of Wistar-Kyoto rats, respectively, p < 0.01). In the adrenal glands of adult SHR, the expression of catecholamine biosynthetic enzymes Th, Ddc, Dbh and Pnmt was decreased along the amounts of dopamine and noradrenaline (50% and 38%, respectively, p < 0.001). The expression levels of Ddc and Dbh enzymes were also downregulated in the sympathetic ganglia of both prehypertensive and adult SHR. At both ages, the density of sympathetic innervation was twofold higher in SHR compared to Wistar-Kyoto rats (p < 0.001). In conclusion, adrenal catecholamine content was increased in prehypertensive SHR, whereas it was reduced in SHR with established hypertension. Surprisingly, downregulation of catecholamine biosynthetic enzymes was observed in both the adrenal medulla and sympathetic ganglia of SHR at both ages. Thus, this downregulation might be a compensatory mechanism that counteracts the vascular sympathetic hyperinnervation seen in SHR of both ages.
The shortening of sarcomeres that co-ordinates the pump function of the heart is stimulated by electrically-mediated increases in [Ca2+]. This process of excitation-contraction coupling (ECC) is subject to modulation by neurohormonal mediators that tune the output of the heart to meet the needs of the organism. Endothelin-1 (ET-1) is a potent modulator of cardiac function with effects on contraction amplitude, chronotropy and automaticity. The actions of ET-1 are evident during normal adaptive physiological responses and increased under pathophysiological conditions, such as following myocardial infarction and during heart failure, where ET-1 levels are elevated. In myocytes, ET-1 acts through ETA- or ETB-G protein-coupled receptors (GPCRs). Although well studied in atrial myocytes, the influence and mechanisms of action of ET-1 upon ECC in ventricular myocytes are not fully resolved. We show in rat ventricular myocytes that ET-1 elicits a biphasic effect on fractional shortening (initial transient negative and sustained positive inotropy) and increases the peak amplitude of systolic Ca2+transients in adult rat ventricular myocytes. The negative inotropic phase was ETBreceptor-dependent, whereas the positive inotropic response and increase in peak amplitude of systolic Ca2+transients required ETAreceptor engagement. Both effects of ET-1 required phospholipase C (PLC)-activity, although distinct signalling pathways downstream of PLC elicited the effects of each ET receptor. The negative inotropic response involved inositol 1,4,5-trisphosphate (InsP3) signalling and protein kinase C epsilon (PKCε). The positive inotropic action and the enhancement in Ca2+transient amplitude induced by ET-1 were independent of InsP3signalling, but suppressed by PKCε. Serine 302 in cardiac myosin binding protein-C was identified as a PKCε substrate that when phosphorylated contributed to the suppression of contraction and Ca2+transients by PKCε following ET-1 stimulation. Thus, our data provide a new role and mechanism of action for InsP3and PKCε in mediating the negative inotropic response and in restraining the positive inotropy and enhancement in Ca2+transients following ET-1 stimulation.
The circadian nature of physiology and behavior is regulated by a circadian clock that generates intrinsic rhythms with a periodicity of approximately 24 h. The mammalian circadian system is composed of a hierarchical multi-oscillator structure, with the central clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus regulating the peripheral clocks found throughout the body. In the past two decades, key clock genes have been discovered in mammals and shown to be interlocked in transcriptional and translational feedback loops. At the cellular level, each cell is governed by its own independent clock; and yet, these cellular circadian clocks in the SCN form regional oscillators that are further coupled to one another to generate a single rhythm for the tissue. The oscillatory coupling within and between the regional oscillators appears to be critical for the extraordinary stability and the wide range of adaptability of the circadian clock, the mechanism of which is now being elucidated with newly advanced molecular tools.
This new edition to the classic book by ggplot2 creator Hadley Wickham highlights compatibility with knitr and RStudio. ggplot2 is a data visualization package for R that helps users create data graphics, including those that are multi-layered, with ease. With ggplot2, it's easy to:
• produce handsome, publication-quality plots with automatic legends created from the plot specification
• superimpose multiple layers (points, lines, maps, tiles, box plots) from different data sources with automatically adjusted common scales
• add customizable smoothers that use powerful modeling capabilities of R, such as loess, linear models, generalized additive models, and robust regression
• save any ggplot2 plot (or part thereof) for later modification or reuse
• create custom themes that capture in-house or journal style requirements and that can easily be applied to multiple plots
• approach a graph from a visual perspective, thinking about how each component of the data is represented on the final plot
This book will be useful to everyone who has struggled with displaying data in an informative and attractive way. Some basic knowledge of R is necessary (e.g., importing data into R). ggplot2 is a mini-language specifically tailored for producing graphics, and you'll learn everything you need in the book. After reading this book you'll be able to produce graphics customized precisely for your problems, and you'll find it easy to get graphics out of your head and on to the screen or page. New to this edition:<
• Brings the book up-to-date with ggplot2 1.0, including major updates to the theme system
• New scales, stats and geoms added throughout
• Additional practice exercises
• A revised introduction that focuses on ggplot() instead of qplot()
• Updated chapters on data and modeling using tidyr, dplyr and broom
Functional impact of cardiac ryanodine receptor (type 2 RyR or RyR2) phosphorylation by protein kinase A (PKA) remains highly controversial. In this study, we characterized a functional link between PKA-mediated RyR2 phosphorylation level and sarcoplasmic reticulum (SR) Ca2 + release and leak in permeabilized rabbit ventricular myocytes. Changes in cytosolic [Ca2 +] and intra-SR [Ca2 +]SR were measured with Fluo-4 and Fluo-5N, respectively. Changes in RyR2 phosphorylation at two PKA sites, serine-2031 and -2809, were measured with phospho-specific antibodies. cAMP (10 μM) increased Ca2 + spark frequency approximately two-fold. This effect was associated with an increase in SR Ca2 + load from 0.84 to 1.24 mM. PKA inhibitory peptide (PKI; 10 μM) abolished the cAMP-dependent increase of SR Ca2 + load and spark frequency. When SERCA was completely blocked by thapsigargin, cAMP did not affect RyR2-mediated Ca2 + leak. The lack of a cAMP effect on RyR2 function can be explained by almost maximal phosphorylation of RyR2 at serine-2809 after sarcolemma permeabilization. This high RyR2 phosphorylation level is likely the consequence of a balance shift between protein kinase and phosphatase activity after permeabilization. When RyR2 phosphorylation at serine-2809 was reduced to its “basal” level (i.e. RyR2 phosphorylation level in intact myocytes) using kinase inhibitor staurosporine, SR Ca2 + leak was significantly reduced. Surprisingly, further dephosphorylation of RyR2 with protein phosphatase 1 (PP1) markedly increased SR Ca2 + leak. At the same time, phosphorylation of RyR2 at serine 2031 did not significantly change under identical experimental conditions. These results suggest that RyR2 phosphorylation by PKA has a complex effect on SR Ca2 + leak in ventricular myocytes. At an intermediate level of RyR2 phosphorylation SR Ca2 + leak is minimal. However, complete dephosphorylation and maximal phosphorylation of RyR2 increases SR Ca2 + leak.
Endothelin (ET), a peptide originally isolated from the supernatants of cultured endothelial cells, exerts a wide variety of biological effects in different tissues. Endothelial-cell-synthesized ET-1 has been proposed to act in a paracrine manner on adjacent smooth muscle cells (SMC) in vivo, with effects that include both vascular reactivity (vasodilation/vasoconstriction) and mitogenesis. This study, by the use of immunocytochemically characterized SMC (rVSMC) isolated from the aortas of spontaneously hypertensive rats, has investigated a possible autocrine role for ET in regulation of the vasculature. Although quiescent cultures of rVSMC apparently did not constitutively express prepro ET-1mRNA, ET-specific transcripts could be induced by a variety of growth factors (transforming growth factor β [TGF-β]; platelet-derived growth factor-AA homodimer [PDGF-A chain]) and vasoactive hormones (angiotensin II [Ang II], arginine-vasopressin, and ET-1 itself). The kinetics for prepro ET-1mRNA induction in rVSMC were characteristically rapid in onset and transient. Down-regulation of protein kinase C by 48 h pretreatment of rVSMC with phorbol ester markedly reduced the subsequent ability of rVSMC to express ET-1 transcripts and secrete ET-1 peptide in response to Ang II. Inducible prepro ET-1mRNA expression was accompanied by a cycloheximide-inhibrtable release of ET-1 peptide into the medium of rVSMC. ET-1 peptide was determined by both radioreceptor- and radioimmunoassay. Stimulated rVSMC accumulated ET-1 (∼200 pg·106 cells-1·4 h-1) at levels that attained biological relevance (∼10-10 M). Sep-pak C18 extracts of medium from stimulated rVSMC elicited contraction of isolated endothelium-denuded rat mesenteric resistance vessels, and this response was characteristically protracted and difficult to "wash out." Synthetic (porcine) ET-1 promoted the expression of transcripts for PDGF-A chain, TGF-β, and thrombospondin in quiescent rVSMC. Such effects of ET-1 on gene expression may be relevant to the mitogenic potential of ET-1 on VSMC. Our findings imply a role for ET-1 in the control of vascular function via both paracrine and autocrine regulatory mechanisms. The expression of prepro ET-1 mRN A and peptide biosynthesis by rVSMC may have both short-term (e.g., vasoconstriction) and long-term (e.g., structural remodeling) consequences. A sustained loop of autocrine stimulation by ET-1 in SMC could contribute toward the pathogenesis of vasospasm and/or atherosclerosis.
Blood pressure exhibits a robust circadian rhythm in health. In hypertension, sleep apnea, and even shift work, this balanced rhythm is perturbed via elevations in night-time blood pressure, inflicting silent damage to the vasculature and body organs. Herein, we examined the influence of circadian dysfunction during experimental hypertension in mice. Using radiotelemetry to measure ambulatory blood pressure and activity, the effects of angiotensin II administration were studied in wild-type (WT) and period isoform knockout (KO) mice (Per2-KO, Per2, 3-KO, and Per1, 2, 3-KO/Per triple KO [TKO] mice). On a normal diet, administration of angiotensin II caused nondipping blood pressure and exacerbated vascular hypertrophy in the Period isoform KO mice relative to WT mice. To study the endogenous effects of angiotensin II stimulation, we then administered a low-salt diet to the mice, which does stimulate endogenous angiotensin II in addition to lowering blood pressure. A low-salt diet decreased blood pressure in wild-type mice. In contrast, Period isoform KO mice lost their circadian rhythm in blood pressure on a low-salt diet, because of an increase in resting blood pressure, which was restorable to rhythmicity by the angiotensin receptor blocker losartan. Chronic administration of low salt caused vascular hypertrophy in Period isoform KO mice, which also exhibited increased renin levels and altered angiotensin 1 receptor expression. These data suggest that circadian clock genes may act to inhibit or control renin/angiotensin signaling. Moreover, circadian disorders such as sleep apnea and shift work may alter the homeostatic responses to sodium restriction to potentially influence nocturnal hypertension.
Jet lag and shift work disorder are circadian rhythm sleep-wake disorders resulting from behaviorally altering the sleep-wake schedule in relation to the external environment. Not everyone who experiences trans-meridian travel or performs shift work has a disorder. The prevalence of jet lag disorder is unclear, approximately 5%-10% of shift workers have shift work disorder. Treatment aims to realign the internal circadian clock with the external environment. Behavioral therapies include sleep hygiene and management of the light-dark and sleep schedule. Pharmacologic agents are used to treat insomnia and excessive sleepiness, and melatonin is used to facilitate sleep and circadian realignment.
The Journal of Physiology and Experimental Physiology have always used UK legislation as the basis of their policy on ethical standards in experiments on non-human animals. However, for international journals with authors, editors and referees from outside the UK the policy can lack transparency and is sometimes cumbersome, requiring the intervention of a Senior Ethics Reviewer or advice from external experts familiar with UK legislation. The journals have therefore decided to set out detailed guidelines for how authors should report experimental procedures that involve animals. As well as helping authors, this new clarity will facilitate the review process and decision making where there are questions regarding animal ethics.
© 2015 The Authors. Experimental Physiology © 2015 The Physiological Society.
Heart disease remains the leading cause of death and disability in the Western world. Current therapies aim at treating the symptoms rather than the subcellular mechanisms, underlying the etiology and pathological remodeling in heart failure. A universal characteristic, contributing to the decreased contractile performance in human and experimental failing hearts, is impaired calcium sequestration into the sarcoplasmic reticulum (SR). SR calcium uptake is mediated by a Ca(2+)-ATPase (SERCA2), whose activity is reversibly regulated by phospholamban (PLN). Dephosphorylated PLN is an inhibitor of SERCA and phosphorylation of PLN relieves this inhibition. However, the initial simple view of a PLN/SERCA regulatory complex has been modified by our recent identification of SUMO, S100 and the histidine-rich Ca-binding protein as regulators of SERCA activity. In addition, PLN activity is regulated by 2 phosphoproteins, the inhibitor-1 of protein phosphatase 1 and the small heat shock protein 20, which affect the overall SERCA-mediated Ca-transport. This review will highlight the regulatory mechanisms of cardiac contractility by the multimeric SERCA/PLN-ensemble and the potential for new therapeutic avenues targeting this complex by using small molecules and gene transfer methods.
The pronounced daily variation in the release of adrenal hormones has been at the heart of the deciphering and understanding of the circadian timing system. Indeed, the first demonstration of an endocrine day/night rhythm was provided by Pincus (1943), by showing a daily pattern of 17-keto-steroid excretion in the urine of 7 healthy males. Twenty years later the adrenal gland was one of the very first organs to show, in vitro, that circadian rhythmicity was maintained. In the seventies, experimental manipulation of the daily corticosterone rhythm served as evidence for the identification of respectively the light- and food-entrainable oscillator. Another 20 years later the hypothalamo-pituitary-adrenal (HPA)-axis was key in furthering our understanding of the way in which rhythmic signals generated by the central pacemaker in the hypothalamic suprachiasmatic nuclei (SCN) are forwarded to the rest of the brain and to the organism as a whole. To date, the adrenal gland is still of prime importance for understanding how the oscillations of clock genes in peripheral tissues result in functional rhythms of these tissues, whereas it has become even more evident that adrenal glucocorticoids are key in the resetting of the circadian system after a phase-shift. The HPA-axis thus still is an excellent model for studying the transmission of circadian information in the body.
A neurogenic component to primary hypertension (hypertension) is now well established. Along with raised vasomotor tone and increased cardiac output, the chronic activation of the sympathetic nervous system in hypertension has a diverse range of pathophysiological consequences independent of any increase in blood pressure. This review provides a perspective on the actions and interactions of angiotensin II, inflammation and vascular dysfunction/brain hypoperfusion in the pathogenesis and progression of neurogenic hypertension. The optimisation of current treatment strategies and the exciting recent developments in the therapeutic targeting of the sympathetic nervous system to control hypertension (for example, catheter-based renal denervation and carotid baroreceptor stimulation) will be outlined.
This study was designed to assess heart performance in young (10-week-old) spontaneously hypertensive rats (SHR) and Wistar-Kyoto
(WKY) rats, in terms of whole heart function in vivo and mechanics of isolated ventricular myocytes in vitro. The data suggest
that left ventricular pressure (LVP) generation is greater, and the maximal velocities of LVP generation and decline are faster
in SHR than in WKY. Two-dimensional morphologic measurements show that SHR myocytes are hypertrophied and that augmented contractile
function is also present in isolated cells as determined by the extent of shortening and velocity of shortening. Relaxation
is also faster at the myocyte level as determined by velocity of relengthening. However, the slope of the relationship between
myocyte peak shortening and velocity of relaxation was similar in both groups. These results suggest that hyperdynamic myocyte
relengthening may reflect changes in elastic recoil from increased shortening rather than intrinsic changes in cellular mechanisms,
which are independent of shortening.
Using fura-2-acetoxymethyl ester (AM) fluorescence imaging and patch clamp techniques, we found that endothelin-1 (ET-1) significantly elevated the intracellular calcium level ([Ca(2+)](i)) in a dose-dependent manner and activated the L-type Ca(2+) channel in cardiomyocytes isolated from rats. The effect of ET-1 on [Ca(2+)](i) elevation was abolished in the presence of the ET(A) receptor blocker BQ123, but was not affected by the ET(B) receptor blocker BQ788. ET-1-induced an increase in [Ca(2+)](i), which was inhibited 46.7% by pretreatment with a high concentration of ryanodine (10 micromol/L), a blocker of the ryanodine receptor. The ET-1-induced [Ca(2+)](i) increase was also inhibited by the inhibitors of protein kinase A (PKA), protein kinase C (PKC) and angiotensin type 1 receptor (AT1 receptor). We found that ET-1 induced an enhancement of the amplitude of the whole cell L-type Ca(2+) channel current and an increase of open-state probability (NPo) of an L-type single Ca(2+) channel. BQ123 completely blocked the ET-1-induced increase in calcium channel open-state probability. In this study we demonstrated that ET-1 regulates calcium overload through a series of mechanisms that include L-type Ca(2+) channel activation and Ca(2+)-induced Ca(2+) release (CICR). ETA receptors, PKC, PKA and AT1 receptors may also contribute to this pathway.
The sympathetic nervous system provides the most powerful stimulation of cardiac function, brought about via norepinephrine and epinephrine and their postsynaptic beta-adrenergic receptors. More than 30 years after the first use of practolol in patients with heart failure beta blockers are now the mainstay of the pharmacological treatment of chronic heart failure. Many aspects of their mechanism of action are well understood, but others remain unresolved. This review focuses on a number of questions that are key to further developments in the field. What accounts for and what is the role of beta-adrenergic desensitization, a hallmark of the failing heart? Is part of this adaptation predominantly beneficial and should therefore be reinforced, another part mainly maladaptive and therefore a target for antagonists? Which lessons can be drawn from studies in genetically engineered mice, which from (pharmaco) genetic studies? Finally, what are promising targets downstream of beta-adrenergic receptors that go beyond the current neurohumoral blockade?
The potential involvement of sympathetic overactivity has been neglected in this population despite accumulating experimental and clinical evidence suggesting a crucial role of sympathetic activation for both progression of renal failure and the high rate of cardiovascular events in patients with chronic kidney disease. The contribution of sympathetic neural mechanisms to the occurrence of cardiac arrhythmias, the development of hypertension, and the progression of heart failure are well established; however, the exact mechanisms contributing to heightened sympathetic tone in patients with chronic kidney disease are unclear. This review analyses potential mechanisms underlying sympathetic activation in chronic kidney disease, the range of adverse consequences associated with this activation, and potential therapeutic implications resulting from this relationship.
Endothelin (ET), a peptide originally isolated from the supernatants of cultured endothelial cells, exerts a wide variety of biological effects in different tissues. Endothelial-cell-synthesized ET-1 has been proposed to act in a paracrine manner on adjacent smooth muscle cells (SMC) in vivo, with effects that include both vascular reactivity (vasodilation/vasoconstriction) and mitogenesis. This study, by the use of immunocytochemically characterized SMC (rVSMC) isolated from the aortas of spontaneously hypertensive rats, has investigated a possible autocrine role for ET in regulation of the vasculature. Although quiescent cultures of rVSMC apparently did not constitutively express prepro ET-1mRNA, ET-specific transcripts could be induced by a variety of growth factors (transforming growth factor beta [TGF-beta]; platelet-derived growth factor-AA homodimer [PDGF-A chain]) and vasoactive hormones (angiotensin II [Ang II], arginine-vasopressin, and ET-1 itself). The kinetics for prepro ET-1mRNA induction in rVSMC were characteristically rapid in onset and transient. Down-regulation of protein kinase C by 48 h pretreatment of rVSMC with phorbol ester markedly reduced the subsequent ability of rVSMC to express ET-1 transcripts and secrete ET-1 peptide in response to Ang II. Inducible prepro ET-1mRNA expression was accompanied by a cycloheximide-inhibitable release of ET-1 peptide into the medium of rVSMC. ET-1 peptide was determined by both radioreceptor- and radioimmunoassay. Stimulated rVSMC accumulated ET-1 (approximately 200 pg.10(6) cells-1 x 4 h-1) at levels that attained biological relevance (approximately 10(-10) M). Sep-pak C18 extracts of medium from stimulated rVSMC elicited contraction of isolated endothelium-denuded rat mesenteric resistance vessels, and this response was characteristically protracted and difficult to "wash out." Synthetic (porcine) ET-1 promoted the expression of transcripts for PDGF-A chain, TGF-beta, and thrombospondin in quiescent rVSMC. Such effects of ET-1 on gene expression may be relevant to the mitogenic potential of ET-1 on VSMC. Our findings imply a role for ET-1 in the control of vascular function via both paracrine and autocrine regulatory mechanisms. The expression of prepro ET-1mRNA and peptide biosynthesis by rVSMC may have both short-term (e.g., vasoconstriction) and long-term (e.g., structural remodeling) consequences. A sustained loop of autocrine stimulation by ET-1 in SMC could contribute toward the pathogenesis of vasospasm and/or atherosclerosis.
Endothelin-1 gene expression is enhanced in the aorta and mesenteric arteries, and possibly other vessels, of deoxycorticosterone acetate (DOCA)-salt hypertensive rats. In contrast, endothelin-1 gene expression is normal or reduced in spontaneously hypertensive rats (SHR). Severe vascular hypertrophy is present in DOCA-salt hypertensive rats but not in SHR. In this study we investigated whether treatment of SHR with DOCA and salt would result in enhanced endothelin-1 expression and at the same time in severe vascular hypertrophy. Increased abundance of endothelin-1 mRNA was found in the aorta and the mesenteric arterial bed of SHR treated simultaneously with DOCA and salt but not when rats were treated with either separately. The wet weight of the aorta and of the mesenteric arterial bed, media thickness, media cross-sectional area, and media-to-lumen ratio of mesenteric small arteries of DOCA-salt-treated SHR were exaggerated beyond what could be explained by the elevation of blood pressure, relative to SHR treated with salt or with DOCA, which did not overexpress vascular endothelin-1. In conclusion, SHR may exhibit enhanced expression of the endothelin-1 gene in blood vessels when treated with DOCA and salt, and associated with this there is severe vascular hypertrophy. These data support the hypothesis of a role of endothelin-1 in vascular hypertrophy.
Endothelins are potent vasoconstrictor peptides produced by the endothelium of blood vessels and other tissues, which could play a potentially important pathogenic role in hypertension. In some hypertensive models, endothelin production in blood vessels is enhanced. We have therefore investigated endothelin-1 gene expression in arteries of 17-week old spontaneously hypertensive rats (SHR) with established hypertension and Wistar-Kyoto control rats (WKY). The abundance of endothelin-1 mRNA in aorta and mesenteric arteries was evaluated by Northern blot analysis. Endothelin-1 mRNA expression was found to be reduced in the aorta of SHR in comparison to the age-matched WKY, whereas it was similar in mesenteric arteries in both strains. These results agree with the vascular content of immunoreactive endothelin-1 which we previously reported, and indicate that reduced or normal vascular endothelin-1 content in SHR is not the result of rapid turnover of the peptide in SHR blood vessels. Together with normal plasma immunoreactive endothelin-1 and normal or reduced responsiveness of blood vessels of SHR to endothelin-1, this indicates that vascular endothelin-1 does not appear to play an important role in the pathogenesis of the elevation of blood pressure in this model of genetic hypertension.
Endothelin-1 (ET-1) is a powerful vasoconstrictor peptide produced in the endothelium of blood vessels that may play an important role in the control of local blood flow and could be involved in the pathogenesis of hypertension. We investigated immunoreactive ET-1 (ir-ET-1) levels in acid extracts from blood vessels of deoxycorticosterone acetate (DOCA)-salt and spontaneously hypertensive rats. We found that segments of thoracic aorta and the mesenteric vascular bed contain significantly more ir-ET-1 (11.84 +/- 0.84 and 17.30 +/- 1.89 fmol, respectively) than uninephrectomized control rats (1.78 +/- 0.20 and 9.19 +/- 0.63 fmol, respectively; p < 0.001). High performance liquid chromatography showed that ir-ET-1 of blood vessels of DOCA-salt hypertensive rats eluted in the same position as synthetic ET-1. Significantly increased ir-ET-1 was localized by immunohistochemistry in endothelial cells of aorta and large and small mesenteric arteries of DOCA-salt hypertensive rats. In contrast to the latter, in spontaneously hypertensive rats, vascular content of ir-ET-1 was similar to that of blood vessels of Wistar-Kyoto control rats, at both 6 and 16 weeks of age. High levels of vascular ET-1 may explain the downregulation of vascular endothelin receptors previously described in DOCA-salt hypertensive rats. Furthermore, this suggests that ET-1 may be involved in the maintenance of high blood pressure in mineralocorticoid hypertension.
This study was undertaken to clarify whether the myocardial dysfunction observed in the hypertensive heart is an intrinsic property of the myocyte or not.
We investigated left ventricular function and contractile function of myocytes from 30-week-old spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). We also evaluated the effect of angiotensin II on contractile function of myocytes from both rats.
The time constant of isovolumic pressure fall was significantly greater in SHR (13.2 +/- 0.6 ms) than in WKY (10.3 +/- 0.5 ms). The extent of shortening in isolated myocytes was significantly higher in SHR (11.3 +/- 0.4%) than in WKY (9.8 +/- 0.4%, P<0.01). Both the normalized maximal velocity of shortening and the normalized maximal velocity of relengthening were significantly greater in SHR (2.12 +/- 0.08 and 2.10 +/- 0.08 s-1; both P<0.01) than in WKY (1.76 +/- 0.06 and 1.75 +/- 0.07 s-1). Angiotensin II caused significant decreases in the extent of shortening, the normalized maximal velocity of shortening and the normalized maximal velocity of relengthening in isolated myocytes from SHR, but these parameters were unchanged in WKY.
These results suggest that left ventricular diastolic dysfunction in SHR is not due to an intrinsic abnormality of the cardiac myocytes, and that angiotensin II suppresses the function of myocytes from hypertrophied hearts.
Transgenic hypertensive TGR(mREN2)27 (TGR) rats, carrying an additional mouse renin gene, have been found to show inverse circadian blood pressure profiles compared to normotensive Sprague-Dawley rats. In order to evaluate the contributions of the suprachiasmatic nucleus (SCN) and the neurohormone melatonin to cardiovascular circadian regulation in TGR(mREN2)27 rats and Sprague-Dawley (SPRD) controls, we investigated the effects of melatonin agonist and antagonist treatment in SCN-lesioned and nonlesioned rats, which were kept under conditions of alternating light and darkness (LD). After destruction of the SCN, circadian rhythmicity in blood pressure, heart rate (HR), and motor activity (MA) was almost abolished in rats of both strains. One week of treatment with a synthetic melatonin agonist S-21634 was not able to restore circadian variation in the parameters monitored. In nonlesioned TGR(mREN2)27 rats and Sprague-Dawley control rats, the melatonin antagonist S-22365 had no suppressive effect on LD-synchronized circadian rhythmicity, indicating that LD itself may have a stronger influence on the SCN than endogenous melatonin.
This study addressed the question whether light-suppressed circadian rhythms in cardiovascular parameters in rats could be restored by melatonin and a synthetic analogue. Blood pressure, heart rate, and locomotor activity were monitored by radiotelemetry in six Sprague-Dawley rats. After synchronization to a 12:12 light/dark (LD) schedule (lights on at 0700 hours, 100 lux), rats were kept in constant light (LL) of low intensity (5-10 lux) for 11 weeks. After 3 weeks of LL, rats received daily intraperitoneal (i.p.) injections at 1900 hours of vehicle, the melatonin agonist S-21767 (5 mg/kg) and melatonin (1 mg/kg). Spectral power, 24-h amplitudes and the differences between day and night means were calculated as measures of circadian rhythmicity. During LL a lengthening of the endogenous period to 26 h was observed, which was accompanied by a continuous decrease in circadian amplitude in all parameters monitored until, in the third week of LL, circadian rhythmicity was almost abolished. Neither vehicle, S-21767 nor melatonin were able to restore circadian rhythms in blood pressure and locomotor activity. In contrast, both agonists induced circadian rhythmicity in heart rate in two out of six rats. The day/night difference in heart rate of all animals was significantly increased by S-21767 and, to a smaller extent, by melatonin, whereas the circadian amplitude was not affected. In conclusion, melatonin and the synthetic agonist were able to partially synchronize circadian rhythmicity in heart rate during constant light, but could not restore circadian rhythms in blood pressure.
Endothelin-1 (ET-1) is a powerful vasoconstrictor peptide and regulator of blood flow that plays an important role in blood pressure (BP) elevation in some models of experimental hypertension such as DOCA-salt rat, DOCA-salt-treated spontaneously hypertensive rats (SHR), stroke-prone SHR, Dahl salt-sensitive rats, angiotensin II-infused rats, and one-kidney, one-clip Goldblatt rats, but not in SHR, two-kidney, one-clip hypertensive rats, transgenic (mREN2)27 rats, or Nomega-nitro-L-arginine methyl ester chronically treated rats. In those models of hypertension in which ET-1 plays a vasoconstrictor role, ET-1 was shown to be overexpressed in the vessel walls, or BP has been lowered by administration of ET(A/B)- and ET(A)-selective receptor antagonists. In these experimental models, endothelin receptor antagonists also regressed vascular growth and inflammation, and improved endothelial dysfunction. Hypertensive rats treated with endothelin antagonists were protected from stroke and renal injury. In hypertensive rats without generalized vascular overproduction of ET-1, expression of ET-1 was often enhanced in intramyocardial coronary arteries, suggesting a role of ET in myocardial ischemia in hypertension. Moderate-to-severe hypertensive patients presented enhanced expression of pre-proET-1 mRNA in the endothelium of subcutaneous resistance arteries, suggesting that this stage of hypertension may respond particularly well to endothelin antagonism. In some hypertensive patients, exaggerated vascular responses to ET-1 were found. Hypertensive patients with coronary artery disease have increased arterial expression of ET-1. Increased plasma levels of immunoreactive ET have been described in African Americans. ET-1 plays an important role in atherosclerosis, for which hypertension is an important risk factor, and in ischemic heart disease and stroke. Endothelin-1 may also be involved in other forms of vascular disease, including pulmonary hypertension, after angioplasty restenosis, after allograft vasculopathy, and vasculitis. Thus, ET-1 may participate in vascular damage in cardiovascular disease and in BP elevation in experimental models and in human hypertension. Endothelin antagonists could become effective disease-modifying agents in different forms of cardiovascular disease.