[Show abstract][Hide abstract] ABSTRACT: The mechanisms responsible for the gender difference in blood pressure (BP) in humans are not clear. Over the past several years we have studied the spontaneously hypertensive rat (SHR) as a model of sex differences in BP control. In the present study, we tested the hypothesis that renal vascular and microsomal epoxyeicosatrienoic acid (EET) levels are higher in females than males, and increasing vascular EETs by blocking epoxide hydrolase with AUDA will reduce BP more in males than females. Renal vascular and microsomal EETs were higher in female SHR than males. Mean arterial pressure (MAP by telemetry) was higher in males than females during the baseline period of 6 days, and although the epoxide hydrolase inhibitor, AUDA, given for 10 days increased renal microvascular EETs in both groups, AUDA did not affect MAP in either group. These data suggest that EETs do not contribute to the sex differences in hypertension in young SHR.
[Show abstract][Hide abstract] ABSTRACT: In postmenopausal women the mechanisms responsible for hypertension have not been completely elucidated and there are no gender specific guidelines for women despite studies showing that blood pressure is not as well controlled to goal in women as in men. In the present study we tested the hypotheses that the sympathetic nervous system and the renal sympathetic nerves contribute to hypertension in aging female rats, that sympathetic activation may be mediated by the melanocortin 3 / 4 receptor (MC3/4R), and that MC3/4R activation may be due to increases in leptin. Alpha-1, beta-1,2-adrenergic blockade reduced blood pressure in both young (3-4 mos) and old (18-19 mos) female (spontaneously hypertensive rats (SHR). Renal denervation attenuated the hypertension more in old females than young females. MC3/4R antagonism with SHU-9119 given intracerebroventricularly had no effect on blood pressure in either young or old females, but significantly reduced blood pressure in old males. Plasma leptin levels were similar in old male and female SHR, and in old vs young females. These data suggest that the hypertension in old female SHR is in part due to activation of the sympathetic nervous system, that the renal nerves contribute to the hypertension, and that the mechanism responsible for sympathetic activation in old females is independent of the MC3/4R.
[Show abstract][Hide abstract] ABSTRACT: In recent years, the interest in studying the impact of sex steroids and gender on the regulation of blood pressure and cardiovascular disease has been growing. Women are protected from most cardiovascular events compared with men until after menopause, and postmenopausal women are at increased risk of cardiovascular complications compared with premenopausal women. The pathophysiological mechanisms have not been elucidated, but are not likely to be as simple as the presence or absence of oestrogens, since hormone replacement therapy in elderly women in the Women's Health Initiative or HERS (Heart and Estrogen/progestin Replacement Study) did not provide primary or secondary prevention against cardiovascular events. Men are also thought to be at risk of cardiovascular disease at earlier ages than women, and these mechanisms too are not likely to be as simple as the presence of testosterone, since androgen levels fall in men with cardiovascular and other chronic diseases. In fact, many investigators now believe that it is the reduction in androgen levels that frequently accompanies chronic disease and may exacerbate cardiovascular disease in men. In the present review, the roles of sex steroids and gender in mediating or protecting against hypertension and cardiovascular disease will be discussed.
[Show abstract][Hide abstract] ABSTRACT: Men are at greater risk for renal injury and dysfunction after acute ischemia-reperfusion (I/R) than are women. Studies in animals suggest that the reason for the sex difference in renal injury and dysfunction after I/R is the protective effect of estrogens in females. However, a reduction in testosterone in men is thought to play an important role in mediating cardiovascular and renal disease in general. In the present study we tested the hypothesis that I/R of the kidney reduces serum testosterone and that contributes to renal dysfunction and injury. Male rats that were subjected to renal ischemia of 40 min followed by reperfusion had a 90% reduction in serum testosterone by 3 hrs post reperfusion that remained at 24 hr. Infusion of testosterone 3 hrs after reperfusion attenuated the increase in plasma creatinine and urinary kidney injury molecule-1 (KIM-1) at 24 hrs, prevented the reduction in outer medullary blood flow, attenuated the increase in intrarenal TNF-α, and the decrease in intrarenal vascular endothelial growth factor at 48 hrs. Castration of males caused greater increases in plasma creatinine and KIM-1 at 24 hrs than in intact males with renal I/R, and treatment with anastrozole, an aromatase inhibitor, plus testosterone almost normalized plasma creatinine and KIM-1 in rats with renal I/R. These data show that renal I/R is associated with sustained reductions in testosterone, that testosterone repletion protects the kidney whereas castration promotes renal dysfunction and injury, and that the testosterone-mediated protection is not conferred by conversion to estradiol.
[Show abstract][Hide abstract] ABSTRACT: Prevalence of hypertension (HT) increases in women after menopause, and there is evidence that HT is not as well controlled in postmenopausal women as men. The reasons for this are not clear, but may be related to the lack of adequate blockade of the systems contributing to HT in women. This study aimed to determine the roles of three of the systems known to contribute to HT in animal studies, angiotensin II (ANG II; enalapril inhibitor), eicosanoids (1-ABT inhibitor), and endothelin (ET(A) receptor antagonist), on blood pressure (BP) in 3 groups of female spontaneously hypertensive rats (SHR), aged 18 mos. Following baseline telemetry BP, three drug periods were performed for 5 days each: single blockade (ABT or enalapril); double blockade (ABT+enalapril or enalapril+ABT); and triple blockade (all 3 drugs). Controls received no treatment until the third period when they received ET(A) receptor antagonist alone. Single drug blockade reduced BP in PMR to similar levels. Double blockade reduced MAP more in ABT+enalapril rats than in the other group (enalapril+ABT). Triple drug blockade reduced BP to similar levels in both groups, but the BP remained above 110 mm Hg. The data suggest that these three systems, Ang II, eicosanoids, and endothelin, contribute together and independently to BP control in old female SHR. However, other systems also contribute to the HT since the BP was not normalized, supporting the notion that HT in postmenopausal women may require complex multi-drug therapy to be better controlled, and that may require the development of additional drugs.
[Show abstract][Hide abstract] ABSTRACT: Numerous experimental studies suggest that oxidative stress contributes to the pathophysiology of hypertension and, importantly, that oxidative stress plays a more definitive role in mediating hypertension in males than in females. Intrauterine growth restriction induced by reduced uterine perfusion initiated at day 14 of gestation in the rat programs hypertension in adult male growth-restricted offspring; yet, female growth-restricted offspring are normotensive. The mechanisms mediating sex differences in blood pressure in adult growth-restricted offspring are not clear. Thus, this study tested the hypothesis that sex-specific differences in renal oxidative stress contribute to the regulation of blood pressure in adult growth-restricted offspring. A significant increase in blood pressure measured by telemetry in male growth-restricted offspring (P<0.05) was associated with a marked increase in renal markers of oxidative stress (P<0.05). Chronic treatment with the antioxidant Tempol had no effect on blood pressure in male control offspring, but it normalized blood pressure (P<0.05) and renal markers of oxidative stress (P<0.05) in male growth-restricted offspring relative to male control offspring. Renal markers of oxidative stress were not elevated in female growth-restricted offspring; however, renal activity of the antioxidant catalase was significantly elevated relative to female control offspring (P<0.05). Chronic treatment with Tempol did not significantly alter oxidative stress or blood pressure measured by telemetry in female offspring. Thus, these data suggest that sex differences in renal oxidative stress and antioxidant activity are present in adult growth-restricted offspring and that oxidative stress may play a more important role in modulating blood pressure in male but not female growth-restricted offspring.
[Show abstract][Hide abstract] ABSTRACT: Preeclampsia is defined as new-onset hypertension with proteinuria after 20 wk gestation and is hypothesized to be due to shallow trophoblast invasion in the spiral arteries thus resulting in progressive placental ischemia as the fetus grows. Many animal models have been developed that mimic changes in maternal circulation or immune function associated with preeclampsia. The model of reduced uterine perfusion pressure in pregnant rats closely mimics the hypertension, immune system abnormalities, systemic and renal vasoconstriction, and oxidative stress in the mother, and intrauterine growth restriction found in the offspring. The model has been successfully used in many species; however, rat and primate are the most consistent in comparison of characteristics with human preeclampsia. The model suffers, however, from lack of the ability to study the mechanisms responsible for abnormal placentation that ultimately leads to placental ischemia. Despite this limitation, the model is excellent for studying the consequences of reduced uterine blood flow as it mimics many of the salient features of preeclampsia during the last weeks of gestation in humans. This review discusses these features.
[Show abstract][Hide abstract] ABSTRACT: Sex differences exist in a variety of cardiovascular and renal diseases, and testosterone may contribute to the discrepancy. Afferent arterioles (Af-Arts) are the major resistance vessels in the kidney, and they play an important role in the development of renal injury and hypertension.
We sought to determine the acute effect and underlying mechanism(s) of action of testosterone on Af-Arts.
The mRNA expression of androgen receptors (ARs) in microdissected Af-Arts was measured by reverse transcription-polymerase chain reaction (RT-PCR). An in vitro microperfusion model was used to measure the diameter of Af-Arts in mice. Nitric oxide (NO) was evaluated by an NO-sensitive fluorescent dye, 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate.
Testosterone had no effect on microperfused Af-Arts when added to the bath. Therefore, we preconstricted the Af-Arts to approximately 30% with norepinephrine (10(-6) M); administration of testosterone (10(-9)-10(-7) M) subsequently dilated the Af-Arts in a dose-dependent manner (P < 0.001; n = 7). The AR mRNA was expressed in microdissected Af-Arts measured by RT-PCR. An AR antagonist, flutamide (10(-5) M), totally blocked the testosterone (10(-8) M)-induced vasodilator effect. Mean (SEM) NO production of the Af-Art wall was increased when testosterone was added to the bath solution after norepinephrine treatment, from 278.4 (12.1) U/min to 351.2 (33.1) U/min (P < 0.05; n = 3). In the presence of NO inhibition with N(G)-nitro-L-arginine methyl ester (3 × 10(-4) M), the testosterone-induced dilatation was blunted compared with norepinephrine (P < 0.05).
Testosterone dilated preconstricted mouse Af-Arts in a dose-dependent manner by activation of ARs and partially mediated by NO.
Gender Medicine 03/2012; 9(2):103-11. · 1.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Blood pressure is typically lower in premenopausal women than in men. However, after menopause, the prevalence of hypertension in women is higher than it is in men. Hypertension is a major risk factor for cardiovascular disease in women and men, but cardiovascular disease is the leading cause of death in women. Furthermore, there is evidence that blood pressure may not be as well-controlled in women as in men, despite the fact that most women adhere better to their therapeutic regimens and medications than do men, and have their blood pressures measured more frequently than do men. This review describes possible mechanisms by which blood pressure may be increased in postmenopausal women.
Current Hypertension Reports 03/2012; 14(3):254-60. · 3.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Androgen levels are lower in obese men as compared with normal weight individuals. However, there are no safety data regarding the chronic use of androgen supplements in middle-aged men. The present study was undertaken to determine the cardiovascular and metabolic effects of chronic (10 weeks) testosterone treatment in male obese Zucker rats, starting at 22 weeks of age, when testosterone levels were significantly decreased. Testosterone supplements increased plasma levels, 10-fold in both obese Zucker rats and lean Zucker rats. In obese Zucker rats, testosterone supplements reduced body weight, plasma insulin, and cholesterol levels and improved the oral glucose tolerance test. None of these parameters were affected in lean Zucker rats. Mean arterial pressure was significantly increased in obese Zucker rats but not lean Zucker rats. Testosterone supplements increased proteinuria and accelerated renal injury in lean Zucker rats only. Thus, treatment of obese men with chronic testosterone supplements should be done with careful monitoring of blood pressure.
[Show abstract][Hide abstract] ABSTRACT: Several clinical studies have investigated the potential benefits of endothelin receptor antagonism in chronic pathologies such as diabetic kidney disease. However, fluid retention and edema have been identified as major side effects of endothelin receptor antagonists. In the present study we hypothesized that avosentan which was described as a predominant ET(A) receptor antagonist would produce fluid retention at high concentrations where non-specific blockade of ET(B) receptors may occur. Incremental doses of the predominant ET(A) receptor antagonist SPP301 (0.003; 0.03; 3 mg/kg) were administered intravenously to anesthetized Sprague-Dawley rats undergoing saline diuresis. Diuresis, glomerular filtration rate, and blood pressure (BP) were monitored. SPP301 decreased urine output (5.6; 34.8; 58.8% decrease from vehicle) and fractional excretion of water (5.7; 31.7; 56.4% decrease from vehicle) in a concentration-dependent manner. Glomerular filtration rate was unchanged while BP was reduced by 10 mmHg only by the highest dose of SPP301. Administration of the ET(B) selective receptor antagonist BQ-788 (3 mg/kg) following SPP301 3 mg/kg did not further decrease urine output or water excretion and was without effect on glomerular filtration rate. These data indicate that increasing concentrations of SPP301 may also block ET(B) receptors and cause antidiuresis. This effect could explain why fluid retention and edema occur during treatment with predominant ET(A) receptor blockers.
[Show abstract][Hide abstract] ABSTRACT: Cardiovascular disease remains the primary cause of death worldwide. In the US, deaths due to cardiovascular disease for women exceed those of men. While cultural and psychosocial factors such as education, economic status, marital status and access to healthcare contribute to sex differences in adverse outcomes, physiological and molecular bases of differences between women and men that contribute to development of cardiovascular disease and response to therapy remain underexplored.
This article describes concepts, methods and procedures to assist in the design of animal and tissue/cell based studies of sex differences in cardiovascular structure, function and models of disease.
To address knowledge gaps, study designs must incorporate appropriate experimental material including species/strain characteristics, sex and hormonal status. Determining whether a sex difference exists in a trait must take into account the reproductive status and history of the animal including those used for tissue (cell) harvest, such as the presence of gonadal steroids at the time of testing, during development or number of pregnancies. When selecting the type of experimental animal, additional consideration should be given to diet requirements (soy or plant based influencing consumption of phytoestrogen), lifespan, frequency of estrous cycle in females, and ability to investigate developmental or environmental components of disease modulation. Stress imposed by disruption of sleep/wake cycles, patterns of social interaction (or degree of social isolation), or handling may influence adrenal hormones that interact with pathways activated by the sex steroid hormones. Care must be given to selection of hormonal treatment and route of administration.
Accounting for sex in the design and interpretation of studies including pharmacological effects of drugs is essential to increase the foundation of basic knowledge upon which to build translational approaches to prevent, diagnose and treat cardiovascular diseases in humans.
[Show abstract][Hide abstract] ABSTRACT: Cardiovascular disease is the leading cause of morbidity and mortality in postmenopausal women. Hypertension is a major risk factor for cardiovascular disease. The mechanisms responsible for postmenopausal hypertension have not been completely elucidated. However, various mechanisms have been implicated to play a role. For example, there is evidence that changes in estrogen/androgen ratios favoring increases in androgens, activation of the renin-angiotensin and endothelin systems, activation of the sympathetic nervous system, metabolic syndrome and obesity, inflammation, increased vasoconstrictor eicosanoids, and anxiety and depression may be important in the pathogenesis of postmenopausal hypertension. There is also evidence that hypertension is less well controlled in aging women than in aging men, but the reasons for this gender difference is not clear. Postmenopausal hypertension is likely multifactorial. Future studies will be necessary to determine the contribution of these systems listed above in mediating postmenopausal hypertension and to design treatment strategies that encompass these mechanisms to improve the quality of life of postmenopausal women as they age.
American Journal of Hypertension 07/2011; 24(7):740-9. · 3.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Blood pressure (BP) increases after menopause. However, the mechanisms responsible have not been elucidated. In this study we tested the hypothesis that 20-hydroxyeicosatetraenoic acids (20-HETE), produced by cytochrome P-450 (CYP450) ω-hydroxylase, contributes to the hypertension in a model of postmenopausal hypertension, aged female spontaneously hypertensive rats (PMR). 1-Aminobenzotriazole, a nonselective inhibitor of arachidonic acid metabolism, for 7 days, reduced BP in PMR but had no effect in young females. Acute intravenous infusion of HET-0016, a specific inhibitor of 20-HETE, over 3 h, also reduced BP in PMR. CYP4A isoform mRNA expression showed no difference in renal CYP4A1 or CYP4A3 but increases in CYP4A2 and decreases in CYP4A8. CYP4A protein expression was decreased in kidney of PMR compared with young females. Endogenous 20-HETE was significantly higher in cerebral vessels of PMR than young females (YF) but was significantly lower in renal vessels of PMR. Omega-hydroxylase activity in cerebral vessels was also higher in PMR but was similar in kidney vessels in both groups. In renal microsomal preparations, endogenous 20-HETE was not different in PMR and young females, but ω-hydroxylase activity was significantly lower in PMR than YF. The data with blockers suggest that 20-HETE contributes to postmenopausal hypertension in SHR. The data also suggest that cerebral production of 20-HETE may be increased and renal tubular production may be decreased in PMR, thus both contributing to their elevated BP.