Since Cannon first formulated the concept of homeostasis 60 years ago, attention has been focused on the corrective responses initiated after the steady state of the organism is perturbed. In this lecture it is argued that the concept of homeostasis should be extended to include the precisely timed mechanisms of the circadian (and circannual) timing system which enables organisms to predict when environmental challenges are most likely to occur. A mature understanding of homeostasis should encompass both "reactive" responses to changes in physiological variables which have already occurred and the "predictive" responses initiated in anticipation of predictably timed challenges. Such predictive responses have particular value because they enable physiological mechanisms to be utilized immediately, even if they involve a delay of several hours, by activating them at a suitable time in advance of a probable challenge. However, conflicts may often occur between predictions and reality. Examples from sleep-wake behavior, thermoregulation, blood volume homeostasis, and the regulation of potassium balance show that predictive responses often compromise the effectiveness of reactive homeostatic mechanisms even to the point of risking the survival of the organism. It must be concluded that the day-night cycle of the natural environment has played a fundamental role in shaping the evolutionary development of homeostatic mechanisms because of the dominating predictability of diurnal changes in illumination, temperature, food availability, and predator activity.
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"Circadian organization is important to enable an organism to maintain equilibrium in response to the daily changes in the external environmental and prepare accordingly . In mammals, a number of circadian patterns (~24-h) have been described, including the timing of endocrine hormone secretion (e.g. "
[Show abstract][Hide abstract] ABSTRACT: Adenosine 5-triphosphate (ATP) and its breakdown products ADP and adenosine can act as extracellular messengers in a range of biological processes. Extracellular adenine nucleotides are metabolized by a number of enzymes including NTPDases and 5'-nucleotidase, which are considered to be the major regulators of purinergic signaling in the blood. Previous work by our group demonstrated that ATPase and ADPase activities in rat serum exhibit a 24-h temporal pattern, with higher enzyme activity during the dark (activity) phase. It was found that stress can cause disruptions in biological circadian rhythms and in the cardiovascular system. Therefore, the aim of the present study was to examine the influence of acute stress exposure upon temporal patterns of NTPDase and 5-nucleotidase enzyme activities in rat blood serum.
Adult male Wistar rats were divided into 4 groups: ZT0, ZT6, ZT12 and ZT18. Each group was subdivided in 4 groups: control, immediately, 6 h and 24 h after one hour of restraint stress. ATP, ADP and AMP hydrolysis were assayed in the serum.
All stressed groups showed significant decreases in all enzyme activities at ZT 12 and ZT 18 when compared with control.
Acute stress provokes a decrease in nucleotidase activities dependent on the time that this stress occurs and this effect appears to persist for at least 24 hours. Stress can change levels of nucleotides, related to increased frequency of cardiovascular events during the activity phase. Altered levels of nucleotides in serum may be involved in cardiovascular events more frequent during the activity phase in mammals, and with their etiology linked to stress.
"Multiple dynamic equilibrium adjustment and regulation mechanisms try to maintain a stable internal condition in endotherms via a process known as " homeostasis " . While homeostasis is typically considered a " reactive " response in order to re-establish a point of equilibrium following a provocation at any time of the day, the chronobiologic view holds that homeostasis also includes a periodic process with varying setpoints in anticipation of predictably timed challenges at different times of the day in a process called " predictive " homeostasis . Thus, in the healthy organism, homeostasis, i.e. the body's ability to regulate stability in its inner environment in response to changing conditions in the outside environment, is paradoxically accomplished by the rhythmic recurrence of biological processes and rhythms in different frequency ranges that co-exist. "
[Show abstract][Hide abstract] ABSTRACT: The neuro-endocrine system function is characterized by a large number of circadian processes that signal each other in sequence with different rhythm phases over 24h. The morning peak of cortisol secretion and the nightly peak in melatonin secretion are well-known physiological phenomena. Thyroid-stimulating hormone (TSH) secretion shows higher levels at night, whereas free thyroxine (FT4) levels do not seem to change with circadian rhythmicity. Similarly, growth hormone (GH) is secreted with higher levels at night, but insulin-like growth factor (IGF)-1 production shows only minor fluctuations over 24h. In order to look for rhythmicity and phasing (acrophase, Ø) in the dynamics of variation over 24h, we investigated adrenal and pineal gland, pituitary-thyroid axis, and GH-IGF-1 axis secretions of cortisol, melatonin, TSH, FT4, GH and total IGF-1 in serum levels every 4h for 24h from 11 healthy men, age: 35–53years. Circadian rhythmicity was evaluated for original values and for the fractional variation (FV) between single time point values that was calculated to evaluate the percentage change in rise and fall. A 24h cosine significantly described the circadian waveform for serum levels in cortisol, melatonin, TSH and GH (Ø=07:48h, 01:35h, 23:32h, 00:00h, respectively), while a 12h cosine significantly described two peaks for serum levels in FT4 (Ø=09:44h and 21:44h, P=0.038), and in IGF-1 (Ø=07:40h and 19:40h, P=0.013). A 24h cosine also significantly described the circadian waveform for FV of cortisol (02:00h), melatonin (22:29h), FT4 (05:14h), and GH (21:19h), while a 12h cosine significantly described two peaks for FV of TSH (04:28h for fall and 16:28h for rise), whereas FV of IGF-1 did not show a rhythmic pattern. Thus, maximal FV estimated by 24h Øs preceded maximal serum levels by ∼6h for cortisol and TSH, ∼5h for FT4, ∼3h for melatonin, ∼2.5h for GH, and ∼1h for IGF-1. When comparing 24h Øs for serum levels of hormone pairs, the peak for melatonin preceded that for cortisol by 6h, the peak for TSH preceded the first peak of FT4 by 10.5h, and the peak for GH preceded that for IGF-1 by 8h. When comparing FV pairs, the peak for melatonin surge preceded that for cortisol by ∼3.5h, the peak for TSH surge preceded that for FT4 by ∼13h, and the peak for GH rise preceded that for IGF-1 ∼10h. In conclusion, the neuro-endocrine system function is characterized by circadian organization, with individual components showing different phasic patterns of time-related variations, and this array of rhythms undoubtedly underlies the maintenance of stable, but rhythmic and thus predictive, homeostatic processes in the human body.
"Most simple, uniform ''constant'' cause and effect relationships, that is, ''reactive homeostasis,'' are oversimplified cases or artifacts of experimental paradigms constructed specifically to force the living system to behave and appear constant. The complexity and cycle stage dependency of cause and effect relationships, that is, ''predictive homeostasis'' (Moore-Ede, 1986), in no way diminishes the reality, importance, or relevance of these relationships. It is, nonetheless, important to freely admit that, although solar activity may have the same temporal pattern as these human time structures, a causal connection may not exist. "
[Show abstract][Hide abstract] ABSTRACT: Periodic episodes of increased sunspot activity (solar electromagnetic storms) occur with 10-11 and 5-6 year periodicities and may be associated with measurable biological events. We investigated whether this sunspot periodicity characterized the incidence of Pap smear-determined cervical epithelial histopathologies and human physiologic functions. From January 1983 through December 2003, monthly averages were obtained for solar flux and sunspot numbers; six infectious, premalignant and malignant changes in the cervical epithelium from 1,182,421 consecutive, serially independent, screening Pap smears (59°9″N, 4°29″E); and six human physiologic functions of a healthy man (oral temperature, pulse, systolic and diastolic blood pressure, respiration, and peak expiratory flow), which were measured ∼5 times daily during ∼34,500 self-measurement sessions (44°56″N, 93°8″W). After determining that sunspot numbers and solar flux, which were not annually rhythmic, occurred with a prominent 10-year and a less-prominent 5.75-year periodicity during this 21-year study span, each biological data set was analyzed with the same curve-fitting procedures. All six annually rhythmic Pap smear-detected infectious, premalignant and malignant cervical epithelial pathologies showed strong 10-year and weaker 5.75-year cycles, as did all six self-measured, annually rhythmic, physiologic functions. The phases (maxima) for the six histopathologic findings and five of six physiologic measurements were very near, or within, the first two quarters following the 10-year solar maxima. These findings add to the growing evidence that solar magnetic storm periodicities are mirrored by cyclic phase-locked rhythms of similar period length or lengths in human physiology and pathophysiology.