Age-related changes in the circadian rhythm of plasma cortisol in man

Longitudinal study of basal cortisol levels in healthy elderly subjects: evidence for subgroups

A group of 51 healthy elderly volunteer subjects participated in a 3- to 6-year longitudinal study of basal cortisol levels. Once per year basal cortisol levels were examined using hourly sampling over a 24-h period. Analyses of three cortisol measures (last measure obtained, mean cortisol levels across years, and the cortisol slope) revealed that the slope of the regression line measuring cortisol levels at each year was the most predictive measure of cortisol secretion over the years in this elderly population. Cortisol levels were shown to increase with years in one subgroup, to decrease in another, and to remain stable in a third. The age of the subjects was not related to either cortisol levels or to the pattern of change in cortisol secretion over years. Free and total cortisol levels were highly correlated and the groups did not differ with regard to plasma corticosteroid binding globulin. No group differences were observed for weight, height, body mass index, pulse, blood pressure and glucose. However, significant group differences were reported for plasma triglycerides levels as well as high density lipoproteins levels. Positive correlations were reported between the obsession/compulsion subscale of the SCL-90 questionnaire and the cortisol slope of subjects. Finally, previously reported group differences in neuropsychological performance are summarized. Thus, there exists considerable variation in hypothalamo-pituitary-adrenal function amongst aged humans. These results are consistent with recent animal studies showing the existence of subpopulations of aged rats which differ in hypothalamo-pituitary-adrenal activity and cognitive efficiency.

Glucocorticoids and aging

Information on the role of glucocorticoids in the aging of vertebrate species is reviewed. There is strong evidence that elevated plasma glucocorticoid levels have a causal role in the rapid deterioration following reproduction in semelparous vertebrate species. If this deterioration is an example of rapid senescence, then it is clear that glucocorticoids can promote aging processes in vertebrate species. However, the evidence that glucocorticoids promote aging in the gradual senescence characteristic of most vertebrate species is not robust. Indeed, there is reason to believe that periods of moderately elevated plasma glucocorticoid levels may retard aging processes in rats, mice, and humans.

Effects of aging on glucose regulation during wakefulness and sleep

Glucose intolerance, reduced sleep efficiency, and disturbed circadian rhythmicity occur in aging. In normal young subjects, glucose regulation is modulated by sleep and circadian rhythmicity. To examine age-related alterations in the temporal pattern of glucose tolerance and insulin secretion, eight modestly overweight healthy older men, eight weight-matched young men, and six young lean men were studied during constant glucose infusion for 53 h. Levels of glucose, insulin, C-peptide, and growth hormone (GH) were measured every 20 min. Rates of insulin and GH secretion were calculated by deconvolution. In older volunteers, sleep ws shallow and more fragmented than in young subjects but was nevertheless associated with robust glucose elevations. However, postsleep increases of insulin secretion were markedly dampened. During wakefulness, the normal morning-to-evening increase in glucose was preserved in the elderly, but insulin secretion failed to increase proportionately. Thus decreased glucose tolerance in aging is associated with insulin resistance and also with a relative insensitivity of the beta-cell to the modulation of glucose regulation by sleep and circadian rhythmicity.

Treatment of delayed sleep phase syndrome

Delayed sleep phase syndrome (DSPS) is a common but little reported cause of severe insomnia. Affected individuals complain of difficulty falling asleep and difficulty awaking at socially acceptable hours. It results from a dysregulation of the circadian sleep-wake cycle. DSPS presents in clinically heterogenous ways as modulated by motivation, psychopathology, drug status, and treatment compliance factors. Patients respond variably to the range of possible treatments. Bright light treatment potentially corrects the circadian abnormality of DSPS. Other treatments reported to relieve some DSPS patients include schedule shifts, drugs, and vitamin and hormone treatments. The safety and efficacy of light treatment have not been conventionally defined, but available information suggests that it is ophthalmologically safe. At present, DSPS must be managed empirically by various methods.

Dose dependent effects of S-20098, a melatonin agonist, on direction of re-entrainment of rat circadian activity rhythms

The chronobiotic properties of melatonin are well documented. For example, following an 8-h phase advance of the light-dark cycle daily injections of melatonin administered at the pre-shift dark onset alter the direction of re-entrainment of rat activity rhythms. Using this 8-h phase advance paradigm, the effects of the melatonin agonist S-20098 (1 mg/kg and 3 mg/kg) on the rat circadian system were compared with those of melatonin. S-20098 altered the direction of re-entrainment in the same manner as melatonin. A study using lower doses of S-20098 showed that the effect on direction of re-entrainment was dose-dependent, with 100% of rats responding at a dose of 100 micrograms/kg. S-20098 may, therefore, have therapeutic potential as a chronobiotic in the treatment of circadian disorders in humans.

Circadian rhythm in type I collagen formation in postmenopausal women with and without osteopenia

A circadian rhythm in the serum concentration of the procollagen type I carboxyl-terminal propeptide (sPICP) has previously been demonstrated in premenopausal women. This study was performed to investigate the circadian rhythm in sPICP in healthy and osteopenic postmenopausal women. Blood samples were taken every third hour for 27 h from three groups of women: 12 early postmenopausal women (aged 55 +/- 2 years; mean +/- SD); 12 late postmenopausal women (aged 73 +/- 1 years); and 12 osteopenic but otherwise healthy late postmenopausal women (aged 73 +/- 1 years). A circadian rhythm in sPICP was found in all three groups, as shown by cosinor analysis (p = 0.000003-0.03). The circadian rhythm in sPICP was significantly different between the osteopenic group and the age-matched healthy group (p < 0.008). The amplitude of the circadian rhythm in sPICP was about twice as high in the osteopenic group, and the time of the maximum tended to be about 3 h later, as compared with the age-matched healthy group. The plasma concentration of osteocalcin, as measured by a recently developed two-site enzyme-linked immunosorbent assay, also showed a circadian rhythm in all three groups (p = 0.0001-0.05), with no significant differences between groups. In conclusion, we have found a significant circadian rhythm in sPICP in both early and late postmenopausal women. In osteopenic women the nightly peak in sPICP is larger and persists later into the night as compared with non-osteopenic women.

Self-esteem and neuroendocrine response to challenge: MacArthur studies of successful aging

The role of self-esteem in modulating patterns of neuroendocrine response to challenge at older ages was examined in 16 healthy 70-yr-olds. Responses to two challenges were examined: (1) a driving simulation designed to reflect a 'real life' challenge situation; and (2) a pharmacologic, corticotropin-releasing-hormone (CRH) challenge (1 micrograms/kg). Both challenges evoked significant elevations in cortisol and adrenocorticotropic hormone (ACTH). Levels of self-esteem were significantly and negatively associated with peak elevations in cortisol in response to the driving simulation challenge (r = -0.51, p = 0.04). ACTH responses showed similar trends (r = -0.41, p = 0.12). Self-esteem levels were not correlated with responses to the CRH challenge. These data indicate that psychological characteristics such as self-esteem may play a role in modulating patterns of neuroendocrine response to cognitive/behavioral challenges in everyday life in older individuals.

The hypothalamic-pituitary-adrenocortical system and sleep in man

This review article summarizes the major findings about the interactions of human sleep structure and the hypothalamo-pituitary-adrenocortical (HPA) system under physiological and pathophysiological conditions, including studies that probe the sleep effects of systemically administered HPA hormones. Human sleep is regulated by a concerted action of various signal compounds acting at sleep-generating neurons whose central organization is not yet fully understood. During nocturnal sleep the endocrine system is remarkably active, the longest established finding being that growth hormone (GH) release is associated with the initiation of sleep and that there is a steep morning rise of cortisol (Weitzman et al., 1966; Takahashi et al., 1968). Moreover, the effects of exogenously administered corticosteroids and of their excessive endogenous release (e.g. Cushing's disease) were recognized more than 20 years ago.

Posture, age, menopause, and osteopenia do not influence the circadian variation in the urinary excretion of pyridinium crosslinks

This study was performed to investigate whether the circadian variation in urinary pyridinium crosslinks is related to physical activity, age, the menopause, and asymptomatic osteopenia. We measured urinary pyridinoline/creatinine (Pyr/Cr) and deoxypyridinoline/creatinine (D-Pyr/Cr) in 9 healthy premenopausal women in two 27 h studies, before and at the end of 5 days of total bed rest. Both Pyr/Cr and D-Pyr/Cr showed highly significant circadian variations, with the peak at night and the nadir during the day (p < 0.001). The 5 days of complete bed rest produced no changes in the circadian pattern, but a general increase of 28% was observed in pyridinium crosslinks. A group of 12 healthy, early postmenopausal women (aged 55 +/- 2 years), 12 healthy, elderly postmenopausal women (aged 73 +/- 1 years), and 12 elderly osteopenic but otherwise healthy women (aged 73 +/- 1 years) were also studied for 27 h. All three groups showed highly significant (p < or = 0.001) circadian variations in the urinary excretion of pyridinium crosslinks. As expected, both Pyr/Cr (p < 0.05) and D-Pyr/Cr (p < 0.001) increased at the time of menopause, but the circadian variations in Pyr/Cr and D-Pyr/Cr were similar in all groups studied. We conclude that the circadian variation in the urinary excretion of pyridinium crosslinks is independent of physical factors. Furthermore, the circadian variation in pyridinium crosslinks was not related to age, menopausal status, or asymptomatic osteopenia.

Coincident plasma ACTH and corticosterone time series: comparisons between young and old rats

Senescence is accompanied by a reduced ability to respond to a variety of physical and behavioral stressors. A sizable literature has been devoted to the interplay between hypothalamic-pituitary-adrenocortical axis dysfunction and senescence; yet, the precise interactions remain an enigma. Adrenocorticotropic hormone (ACTH) is secreted in pulsatile bursts generating complex signals in the plasma compartment that must be "read" by adrenocortical cells in order to initiate appropriate secretory responses. We have previously demonstrated subtle differences between young and old rats in the pattern of fluctuations in plasma ACTH concentrations over time, despite no difference in mean levels. The present work addressed the physiological significance of these differences in the plasma ACTH signal by analyzing the corresponding plasma corticosterone concentration time series and the relationship between these two hormones over time. Time series of integrated 10-min ACTH and corticosterone concentrations were collected over 4 h at the time of diurnal activation and analyzed in the time and frequency domains. The time of onset of the diurnal surge occurred 20 min later in old rats, and the ratio of corticosterone to ACTH was less at the time of onset and peak of the diurnal surge. Corticosterone levels were lower in old rats and mean ACTH and corticosterone levels were correlated in young but not old rats, as were maximum levels of the two hormones. Cross-correlation of ACTH and corticosterone time series and comparison of spectra were consistent with smoother fluctuations in plasma corticosterone in old animals with less variability at time scales less than 55 min. We conclude that age may be associated with a delay in diurnal activation of the HPA axis, a loss of sensitivity of adrenal corticosterone secretion to plasma ACTH levels, and a relative loss of high frequency variability in the corticosterone signal, as seen in many physiological systems with age.

A neuroendocrine overview of aging

The neuroendocrine changes associated with aging are numerous, and tend to vary quantitatively, if not qualitatively between species. The extent to which neuroendocrine dysfunction contributes to the undesirable features of aging remains to be fully determined. Nevertheless, although the aging process itself may not have a neuroendocrine basis, identification and correction of the associated neuroendocrine dysfunction may be important in enhancing the quality of life during this period.

Perioperative glucocorticoid coverage. A reassessment 42 years after emergence of a problem

OBJECTIVE

The authors review the historical basis for the provision of perioperative glucocorticoid coverage, and detail the evolution in the understanding of the role of the hypothalamic-pituitary-adrenal cortical (HPA) axis in response to physical stressors. New recommendations are proposed for glucocorticoid-dependent patients who require anesthesia and surgery.

SUMMARY BACKGROUND DATA

In 1952, a patient developed surgery-associated adrenal insufficiency as a result of preoperative withdrawal from glucocorticoid therapy. That case report, and one other in the ensuing 12 months, prompted the publication of recommendations for perioperative glucocorticoid coverage, which became the standard of care. The understanding of the role of the HPA axis in the stress response has been subsequently refined; however, recommendations for perioperative glucocorticoid coverage have not been altered in parallel.

METHODS

Studies were identified beginning with the first reports of the physiologic actions of the adrenal glands (1855) and the description and clinical use of cortisone (1930-1993). Studies were selected for review if they were related to or evaluated the provision of stress-related glucocorticoid administration. All clinical studies were evaluated to determine the basis for the provision of perioperative glucocorticoid coverage and the validity of the data used to justify these conclusions.

CONCLUSIONS

Clinical and experimental evidence support the concept that the current amount of perioperative glucocorticoid coverage is excessive and has been based on anecdotal information. New recommendations are proposed which suggest that the amount and duration of glucocorticoid coverage should be determined by: a) the preoperative dose of glucocorticoid taken by the patient, b) the preoperative duration of glucocorticoid administration, and c) the nature and anticipated duration of surgery.

Morning bright light therapy for sleep and behavior disorders in elderly patients with dementia

Fourteen inpatients with dementia showing sleep and behavior disorders (average age = 75 years), and 10 control elderly people (average age = 75 years) were carefully observed for 2 months. Four weeks of morning light therapy markedly improved sleep and behavior disorders in the dementia group. The measurement of sleep time and the serum melatonin values suggests that sleep and behavior disorders in the dementia group are related to decreases in the amplitude of the sleep-wake rhythm and decreases in the levels of melatonin secretions. Morning light therapy significantly increased total and nocturnal sleep time and significantly decreased daytime sleep time. These results indicate that morning bright light is a powerful synchronizer that can normalize disturbed sleep and substantially reduce the frequency of behavior disorders in elderly people with dementia.

Effects of age on spontaneous cortisolaemia of normal volunteers and depressed patients

The aim of this study was to characterize the relationships between age and endogenous cortisol secretion in healthy controls and in major depressed patients between 18 and 58 years of age. Toward this end, the authors measured morning basal plasma cortisol secretion every 30 min from 0900 h until 1100 h and computed the integrated morning cortisol secretion in 80 normal controls and 118 major depressed patients. A significant negative correlation between age and plasma morning cortisol was found in normal volunteers but not in major depressives. The observed decrease in cortisol secretion with age in normal controls older than 35 years does not occur in major depressives. The middle age (+/- 35 years) appears to be an important turning point in hypothalamo-pituitary-adrenal (HPA)-axis function of normal persons vs. major depressives.

Studies of nocturnal penile tumescence and sleep electroencephalogram in patients with major depression and in normal controls

Nocturnal penile tumescence (NPT), sleep electroencephalogram and testosterone secretion were investigated in 25 nonmedicated male patients with an acute episode of major depression. Twelve patients were reassessed after a stable remission and withdrawal of antidepressants. Four of the 25 patients had no NPT activity during acute depression, but this was reversed after recovery. The area under the NPT curve increased after remission, whereas all other NPT variables remained unchanged. Nocturnal testosterone secretion was enhanced after recovery, whereas the sleep structure remained unchanged. The NPT findings for the depressed patients did not differ from those for a control group, even though the latter group was younger. Hence, there are no general NPT changes that could be used to separate depressed patients and normal controls. However, a lack of NPT seems to be a possible, reversible symptom of depression in men.

Rhythmicity and response to A.M. and P.M. CRH challenge in elderly subjects

Cortisol and ACTH exhibit circadian rhythmicity, peaking in the early morning. These peaks are associated with increased activity and alertness. We sought to determine whether self-reported daily rhythms predict outcome of a.m. and p.m. CRH challenge in elderly subjects. We surveyed 96 elderly subjects to determine daily rhythms in activity levels, mood, alertness, and performance. Seven healthy subjects were given a cumulative activity score reflecting propensity toward morningness or eveningness. Subjects underwent CRH challenge testing during the morning and evening hours of different days. Baseline plasma ACTH and cortisol concentrations were higher in the morning than in the evening and lower values were associated with lower activity scores (i.e., greater morningness). No trends were apparent between activity score and net hormone response or percent change in hormone concentration.

Diurnal variation in serum markers of type I collagen synthesis and degradation in healthy premenopausal women

There are several indications that the functions of human osteoblasts and osteoclasts have circadian rhythms with peak activities occurring at night. It is not known, however, whether the principal function of these cells, namely synthesis and degradation of the organic matrix of bone, of which about 90% is type I collagen, also has a circadian rhythm. This was therefore investigated for both the formation of type I collagen and the degradation of type I collagen in bone using two newly developed serum markers: the serum concentration of the carboxy-terminal propeptide of type I procollagen (PICP) as a marker of formation and the serum concentration of the carboxy-terminal pyridinoline cross-linked telopeptide of type I collagen (ICTP) as a marker of degradation. PICP and ICTP were measured by RIA in samples taken every 3 h over a 24 h period in 12 healthy premenopausal women (age 32 +/- 5 years, mean +/- SD). Both PICP (p = 0.003) and ICTP (p = 0.00003) showed a significant circadian rhythm, with about 20% higher values at night than in the afternoon. We conclude that serum markers of both the formation of new type I collagen and the degradation of old type I collagen in bone exhibit a clear circadian rhythm, with increased activity of both osteoblasts and osteoclasts at night. The etiology of this circadian rhythm is still unknown.

[Sleep in normal aging]

Sleep in the elderly is characterized by a decrease in the ability to stay asleep resulting in a more fragmented sleep. Spindles are less frequent and less ample, shorter, without an increase during the night contrary young subjects. Delta activity in slow wave sleep is decreased in the 0.5-2 Hz frequency band only. REM sleep occurs earlier the first REM period duration increases. The REM sleep appearance is almost uniform during the night. REMs density does not increase toward the end of the sleeping period. The sleep-wake circadian rhythm is advanced (bedtime and morning awakening occur earlier). The temperature rhythm is also advanced. The rise in temperature after the nadir begins earlier for females and the initial ascent is more rapid. This explains why women wake up earlier and sleep for shorter durations than men. The nocturnal and diurnal mean plasmatic norepinephrine values increase. The rhythm of cortisol secretion is advanced. The GH and melatonin peaks of secretion are decreased. The acrophase of melatonin rhythm is occurring later in the elderly. These results suggest a weakening of circadian structure in the course of aging and an altered relationship between the pacemakers driving melatonin and cortisol circadian rhythms.

Serum dehydroepiandrosterone sulfate in Alzheimer's disease and in multi-infarct dementia

Circulating levels of dehydroepiandrosterone sulfate (DHEAS) and cortisol were studied in 86 patients with dementia; 45 with Alzheimer's disease and 41 with multi-infarct dementia. Compared to an elderly control group, after adjustment for age and sex, patients with Alzheimer's disease were found to have lower serum levels of DHEAS. We found a covariation between serum albumin and DHEAS levels, which may be of importance regarding peripheral hormone concentration in patients with dementia. These findings may provide evidence for a role of DHEAS in amnestic disorder in humans, either reflecting or contributing to the course of dementing diseases.

The effects of depression and age on the Horne-Ostberg morningness-eveningness score

Effects of depression and age on the Horne-Ostberg morningness-eveningness scale in human volunteers were assessed. Thirty-nine healthy outpatients with current DSM-IIIR depression, free of recent substance abuse or confounding medications, were compared to 39 age- and sex-matched controls. Patients reported greater 'eveningness' than controls (P = 0.014, Wilcoxon signed-ranks test). There was multimodality in the distribution of Horne-Ostberg scale scores in the depressed group, but a normal distribution in controls. Pearson's correlation of age vs. Horne-Ostberg score was positive (r = 0.42-0.55). Depression and age influence the Horne-Ostberg score. Potential multimodality of circadian phase in the depressed group deserves further study.

Effect of age on the cortisol response to human corticotropin-releasing hormone in depressed patients pretreated with dexamethasone

A combined dexamethasone-human corticotropin-releasing hormone (hCRH) test was applied to 63 individuals--44 patients with major depressive episode (22 male, age 49.5 +/- 13.4 years, and 22 female, 44.6 +/- 11.9 years) and 19 normal male controls (age 42.0 +/- 16.8 years). In normal controls, premedication with 1.5 mg dexamethasone at 11:00 PM substantially inhibited the stimulated release (expressed as area under the time course curve) of cortisol on the day after 100 micrograms hCRH was administered at 3:00 PM. In contrast, depressives responded with significant rises in cortisol (normal controls, 4.1 +/- 4.0 x 10(3) ng/ml/min; depressives, 12.7 +/- 8.3 x 10(3) ng/ml/min; p less than 0.01). Multiple stepwise regression analysis disclosed significant effects of age (T = 3.55, p less than 0.01) and severity of depression (T = 5.42, p less than 0.01) on cortisol release in patients. Such an influence of age upon pituitary-adrenocortical regulation was absent among healthy controls. We postulate that the underlying mechanisms involve changes in corticosteroid receptors in the brain of depressives, impairing the sensitivity with which the brain-pituitary system can detect the dexamethasone feedback signal. Altered glucocorticoid neuroregulation in depression is apparently accelerated by the aging process.

Neuroendocrine rhythms and sleep in aging men

To delineate the physiological effects of aging on basal levels and temporal patterns of neuroendocrine secretions, the 24-h profiles of cortisol, thyroid-stimulating hormone (TSH), melatonin, prolactin, and growth hormone (GH) levels were simultaneously obtained at frequent intervals in eight healthy, active elderly men, age 67-84 yr and in eight young male adults, age 20-27 yr. The study was preceded by an extended period of habituation to laboratory conditions, and sleep was polygraphically recorded. Mean cortisol levels in the elderly were normal, but the amplitude of the circadian rhythm was reduced. Circulating levels of daytime and nighttime levels of both TSH and GH were greatly diminished in old age. In contrast, prolactin and melatonin concentrations were decreased during the nighttime only. The circadian rises of cortisol, TSH, and melatonin occurred 1-1.5 h earlier in elderly subjects, and the distribution of rapid-eye-movement stages during sleep was similarly advanced, suggesting that circadian timekeeping is modified during normal senescence. Despite perturbations of sleep, sleep-related release of GH and prolactin occurred in all elderly men. Age-related decreases in hormonal levels were associated with a decrease in the amplitude, but not the frequency, of secretory pulses. These findings demonstrate that the normal process of aging involves alterations in the central mechanisms controlling the temporal organization of endocrine release in addition to a reduction of secretory outputs.

Age-related alterations in pulsatile secretion of TSH: role of dopaminergic regulation

To investigate the influence of aging on dopaminergic modulation of pulsatile thyrotropin (TSH) secretion, we examined changes in circulating TSH levels during the day and night, with and without a dopamine antagonist metoclopramide, in healthy young (20-35 yr old) and old (69-83 yr old) subjects, with the use of cluster analysis. Baseline thyroid function tests including serum thyroxine, 3,5,3'-triiodothyronine (T3), T3 resin uptake, and TSH and the response of TSH to thyrotropin-releasing hormone were within normal limits in young and old subjects, and antimicrosomal and anti-thyroglobulin antibodies were absent in all participants. Pulsatile TSH secretion was identified in all subjects, and as a group there were significant increases in nocturnal peak height (P less than 0.01), amplitude (P less than 0.01), and mean TSH (P less than 0.001). TSH pulse amplitude increased 160% (P less than 0.05) at night compared with day in the young but was unchanged at night in the old. After the administration of metoclopramide there was a significant increase in peak height (P less than 0.01), amplitude (P less than 0.01), and mean TSH (P less than 0.01). However, the effect of metoclopramide was different in young and old subjects. In the young, daytime administration of metoclopramide increased TSH pulse height (P less than 0.02) and mean TSH (P less than 0.05); pulse parameters remained unchanged at night. In comparison, in old subjects after metoclopramide, pulse parameters were unchanged during the day but pulse amplitude significantly (P less than 0.01) increased at night. TSH pulse frequency remained stable with age and was unaltered after metoclopramide.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of body temperature rhythms between healthy elderly and healthy young adults

The fact that the elderly are usually aware of early sleep onset and early morning awakening shows that the phase of sleep-wake rhythms in the elderly is more advanced than that in young adults. Since it has been suggested that human sleep onset, morning awakening, sleep period and depth of sleep are highly influenced by body temperature rhythms, rectal temperature rhythms were analyzed in 7 healthy elderly and 7 healthy young adults under the condition with time cue. Although a significant 24-hour period was found in the rhythms for all subjects, the phase of the rhythms in the elderly was more advanced than in the young adults. Moreover, a significant inverse correlation was observed between age and acrophase time in the elderly.

Research on sleep, circadian rhythms and aging: applications to manned spaceflight

Disorders of sleep and circadian rhythmicity are characteristic of both advancing age and manned spaceflight. Sleep fragmentation, reduced nocturnal sleep tendency and sleep efficiency, reduced daytime alertness, and increased daytime napping are common to both of these conditions. Recent research on the pathophysiology and treatment of disrupted sleep in older people has led to a better understanding of how the human circadian pacemaker regulates the timing of the daily sleep-wake cycle and how it responds to the periodic changes in the light-dark cycle to which we are ordinarily exposed. These findings have led to new treatments for some of the sleep disorders common to older individuals, using carefully timed exposure to bright light and darkness to manipulate the phase and/or amplitude of the circadian timing system. These insights and treatment approaches have direct applications in the design of countermeasures allowing astronauts to overcome some of the challenges which manned spaceflight poses for the human circadian timing system. We have conducted an operational feasibility study on the use of scheduled exposure to bright light and darkness prior to launch in order to facilitate adaptation of the circadian system of a NASA space shuttle crew to the altered sleep-wake schedule required for their mission. The results of this study illustrate how an understanding of the properties of the human circadian timing system and the consequences of circadian disruption can be applied to manned spaceflight.

Regulation of basal ACTH secretion by corticosterone is mediated by both type I (MR) and type II (GR) receptors in rat brain

The mechanisms involved in the physiology of the secretion of ACTH are reviewed. The secretion is regulated by the biological consequences of the occupancy of high affinity mineralocorticoid (MR) and lower affinity glucocorticoid receptors (GR) for corticosterone at specific sites of the rat brain. The regulation by this mechanism of basal secretion during the circadian rhythm, the effect of adrenalectomy and of corticosterone replacement is discussed. Experiments with RU486, a specific glucocorticoid antagonist, suggest that occupancy of both MR and GR is required for normal control of ACTH at the time of peak activity. The occupancy of the GR for a few hours per day apparently suffices to maintain steady levels of the products of GR-responsive genes throughout the body.

Circadian rhythms of insulin needs and actions

Circadian rhythms of insulin needs and action are a frequently discussed issue that is both of considerable physiological interest and of clinical importance in case of insulin substitution in type 1 diabetes. Basally, insulin is released in a pulsatile fashion which seemingly is erratic but at close analysis displays 'free-running' cyclical rhythmicity of 8-30 min duration that possibly guarantees optimal insulin action. This basal mode of insulin secretion is subject to a multitude of endogenous control systems that act on the B-cell both in a stimulatory (e.g., beta-agonists, glucagon as well as glucose and amino acids) and an inhibitory fashion (e.g., alpha-agonists, somatostatin). Since impairment of target cell sensitivity to insulin action and hyperglycemia may be caused by the stress hormones, cortisol, epinephrine and growth hormone included, with in part intrinsic rhythmicity, as well as by dehydration and by prolonged insulin withdrawal, a secondary feed-back signal on insulin release may easily be induced by rising blood glucose levels. In that modulators of insulin release and action are themselves secreted in a circadian fashion they tend to secondarily imprint the mode of insulin release. Therefore, any difference between a daily maximum and minimum in plasma insulin concentration besides its free-running short-term rhythmicity has to be regarded as a composite secondary circadian rhythm. It is in particular due to variable secondary early-morning and late-afternoon insulin resistance.

Circadian rhythms of melatonin and cortisol in aging

The relationship of age to the circadian rhythms of melatonin and cortisol was investigated in 44 men and 27 women (age range 19-89 years). Subjects were physically and psychiatrically normal. Four hourly serial blood samples were drawn from 8:00 AM until 8:00 AM the next day, with additional samples at 10:00 PM and 2:00 AM. The indoor illumination was restricted to 300 lux during day and 50 lux during the night. Plasma melatonin and cortisol were estimated by radioimmunoassay. Results show that the means of melatonin and cortisol values decreased significantly with age when the subjects were divided into three age groups, i.e., 19-25 years, 42-65 years, and 66-89 years. They also showed a significant negative correlation with age. The acrophases of the two hormonal rhythms, however, showed different relationships to age. The acrophase of melatonin rhythm showed a positive correlation with age (r = 0.38, p less than 0.001), and cortisol showed a negative correlation with age (r = -0.56, p greater than 0.001). It is suggested that this may indicate a weakened responsiveness of the circadian system in the elderly to the day-night cycle and an altered relationship between the pacemakers driving melatonin and cortisol circadian rhythms. This may thus represent a biomarker for the intrinsic process of the aging of the brain.

Endocrinology in aging

Aging is a time of reduced adaptability to metabolic perturbation. This is particularly true in endocrinology which, after all, is the science of chemically regulated biologic systems. There is no evidence that equilibrium concentrations of the principal hormones are altered with age. However, the systems utilized to reach those equilibria become progressively taxed, and new equilibria may be achieved reflecting that regulatory problem. Thus, with advancing age there are significant alterations in hormone production, metabolism, and action. Some of these changes may play a role in the pathophysiology of senescence, although the evidence for that is limited. The magnitude of age-related alterations is highly variable and sex dependent. Whereas only subtle changes occur in pituitary dynamics, adrenal gland physiology, and thyroid function, the changes in glucose homeostasis, reproductive function, and calcium metabolism are more apparent. In the elderly, the interpretation of endocrine tests should reflect the nutritional status of the patient and the presence of coexisting illnesses. In this review, we describe the principles of endocrinology in the geriatric population and elaborate on the changes in specific glandular functions with aging. We also define strategies of evaluation and management protocols appropriate for the elderly with suspected endocrine dysfunction.

Implications of altered limbic-hypothalamic-pituitary-adrenocortical (LHPA)-function for neurobiology of depression

The current article suggests that the neuroendocrine system constitutes a bidirectional link between the brain and humoral homeostasis in the periphery. Any change of neuronal activity in the brain--regardless whether induced by external stimuli or endogenous errors of metabolism--may result in altered composition of gene products. Among these are peptides which directly or indirectly alter endocrine activity and may concomitantly induce a variety of behavioral effects. This has been experimentally demonstrated by neuropeptidergic manipulation of sleep-electroencephalographic (EEG) measures and behavioral studies in animals. An integral part of the neuroendocrine communication are effects of peripheral hormones upon brain structures and their interactions with the immune system. Within this framework all hormones of the limbic-hypothalamic- pituitary-adrenocortical (LHPA)-axis play a dominant role, because: (1) corticotropin-releasing hormone (CRH) was shown to integrate centrally behavioral and metabolic responses to stress; and (2) corticosteroids exert a host of neurochemical changes within the CNS which by far exceed their primary endocrine feedback action. As a corollary, hyperexposure to corticosteroids induces widespread changes of neuronal cell biology which are of clinical significance for depression research (e.g. neuronal cell loss in the hippocampus, down-regulation of glucocorticoid receptors within monoaminergic neurons). Clinical neuroendocrine research over the past years focussed upon evaluation of pathophysiology underlying dexamethasone resistant cortisol levels or hypercortisolism linked to depression and utilized advanced methods for multihormonal analysis and newly synthesized neuropeptides (e.g. CRH) for challenge studies in combination with neurophysiological assessments.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related differences and circadian and seasonal variations of myelopoietic progenitor cell (CFU-GM) numbers in mice

The effect of aging on the myelopoietic progenitor cell (CFU-GM) numbers in mice was studied with special emphasis on biological rhythms in hemopoiesis. Female C3H mice, 16-, 21- and 26-month-old, were investigated versus 3-month-old controls every 3 hours during the 24-h period at three different times of the year. Strong circadian rhythms were observed in both CFU-GM concentration and content in the femur of all age-groups. The amplitudes and the 24-h mean values were declining in mice aged 21 and 26 months. From 16 months of age, a significant advance of circadian peak phases was observed. The overlapping was variable during the 24-h period. The present results may explain previous inconsistencies regarding myelopoietic progenitor cell numbers in aging mice. Some seasonal differences in rhythmicity patterns were also observed. Fitting of original data to single sinus functions was highly significant, although important details sometimes were obscured.

Alterations of cell cycle distribution in the bone marrow of aging mice measured by flow cytometry

The effect of aging on the cell cycle distribution in bone marrow cells was measured by flow cytometry with special reference to the lability in bone marrow physiology. Female C3H mice were examined every 3 h during a 24-h period at the age of 16, 21 and 26 months, vs 3-month-old control mice. Considerable circadian fluctuations were found in the different cell cycle phases in young mice. The rhythmicity patterns were different when comparing different months. In aging mice the variations were dampened, while consistent age-related phase shifts were not seen. The maximal 24-h mean numbers of cells in all three cell phases, but especially the S and G2 phases were reached at 21 months. The relative number of S and G2 phases were significantly reduced in 26-month-old mice, indicating an age-related shift of the proliferative capacity. The present findings are discussed in relation to age-related changes in granulopoiesis and the increase of myelotoxic effects during cancer chemotherapy in aging individuals.

Stable adrenocorticotropin-stimulated 11-beta-hydroxylase activity but loss of age-related changes in patients with hypercortisolemia

Eleven-beta-hydroxylase activity was measured before and after acute adrenocorticotrophic hormone (ACTH) stimulation in 28 controls, 25 depressed Dexamethasone Suppression Test (DST) suppressors, 13 DST nonsuppressor patients, and 8 patients with Cushing's syndrome to investigate changes in states of cortisol hypersecretion. Eleven-beta-hydroxylase activity was equivalent among groups both before and after stimulation. Such 11-beta-hydroxylase stability, however, resulted in higher cortisol and 11-deoxycortisol poststimulation levels in both depressed DST nonsuppressors and Cushing's patients than in controls. Basal 11-beta-hydroxylase activity is positively correlated and 11-deoxycortisol is negatively correlated with age in controls and DST suppressors, but not in the patients tested with evidence of cortisol hypersecretion. These findings suggest that in vivo basal 11-beta-hydroxylase activity rises gradually with age, but does not rise after acute administration of exogenous ACTH. The age relationship is lost in states of cortisol hypersecretion, but the lack of response to acute exogenous ACTH is not affected.

Circadian rhythms of peripheral blood leukocytes in aging mice

The effect of aging on white blood cell numbers was studied with special reference to the lability in blood cell physiology. Thus, the total numbers of leukocytes, polymorphonuclear granulocytes (PMNs) and lymphocytes were investigated in C3H mice, 3-month-old mice vs. mice aged 16, 21 and 26 months. Strong circadian rhythms were observed in the different cell classes, while there were insignificant seasonal changes. Even the oldest mice had significant variations, especially in the total leukocyte numbers and the PMNs. Subtle age-related shifts in the rhythmicity patterns were indicated. When comparing the 24-h means, there was a shift between the different white blood cell classes. A permanent reduction of the lymphocyte number was observed from the age of 16 months, while the number of PMNs steadily increased in the aging mice. The present results may explain inconsistencies among previous studies, demonstrating the significance of a chronobiological approach.

Comparison of saliva and plasma 17-hydroxyprogesterone time-course response to hCG administration in normal men

17-Hydroxyprogesterone (17-OHP) time-course response to hCG (5000 IU) was studied simultaneously in the saliva and the plasma of 12 adult healthy men. Baseline levels in plasma and saliva were: 1.0 +/- 0.1 ng/ml (mean +/- SEM) and 24 +/- 2 pg/ml respectively. After hCG, a biphasic pattern was observed in both fluids with a similar early response but the peak elicited at 33 h in plasma was not observed in saliva where the levels were lower than those recorded at 24 h. Since saliva steroids are believed to reflect the plasma non-protein bound fraction, this difference was assumed to be due to the decrease of the unbound fraction of plasma 17-OHP in the late afternoon as a consequence of the increase of CBG-bound fraction since at that time cortisol levels are low. The ratio of saliva to plasma 17-OHP levels was significantly correlated with plasma cortisol levels: r = 0.44 (P less than 0.01; n = 140). However the similar response in saliva at 24 and at 48 h after hCG allows the evaluation of the endocrine testicular function using saliva instead of plasma.

The effects of aging on the circadian rhythm of serum cortisol in the dog

The purpose of this study was to determine if aging affects the circadian rhythm of serum cortisol. Female beagle dogs belonging to three age groups were used: adult (3.3 +/- 0.6 (SD) years), old (12.1 +/- 0.3 years), and puppies (8.4 +/- 0.2 weeks). Blood samples were collected by cephalic or jugular venipuncture at 3-h intervals during three 24-h periods and analyzed for total serum cortisol concentrations by radioimmunoassay. The circadian rhythm was present in the serum cortisol of adult animals, but no significant changes during a 24-h period could be detected in the old animals. No circadian rhythm in serum cortisol was present in the puppies. It is concluded that the circadian rhythm in plasma cortisol is disrupted in old animals and is not yet developed in puppies.