The response of plasma testosterone, LH and FSH to oral administration of cortisol or dexamethasone was studied for 26 h in 6 groups of 12 normal adult males. Twenty-four hour treatment with cortisol (60 mg at 1000 h, followed by 30 mg at 2 h intervals) or with dexamethasone (6 mg at 1000 h, followed by 3 mg at 6 h intervals) was without effect on testosterone during the day but suppressed the nocturnal rise completely. LH and FSH did not decrease at any time during the day and showed a highly significant increase during the second part of the night. Short-term treatment (1000–1600 h, 1600–2200 h or 2400 h–0800 h) with cortisol was less effective in suppressing the nocturnal rise in testosterone. It was concluded that administration of cortisol leading to plasma levels as seen under treatment with ACTH suppresses testosterone by abolishing or flattening the nocturnal rise. This effect was not mediated by changes in LH or FSH. Our data suggest that the ACTH-induced suppression of testosterone is d...

Cortisol-induced suppression of plasma testosterone in normal adult males.

While much is known about the mechanisms that underlie sleep and circadian rhythms, the investigation into sex differences and gonadal steroid modulation of sleep and biological rhythms is in its infancy. There is a growing recognition of sex disparities in sleep and rhythm disorders. Understanding how neuroendocrine mediators and sex differences influence sleep and biological rhythms is central to advancing our understanding of sleep-related disorders. While it is known that ovarian steroids affect circadian rhythms in rodents, the role of androgen is less understood. Surprising findings that androgens, acting via androgen receptors in the master “circadian clock” within the suprachiasmatic nucleus, modulate photic effects on activity in males point to novel mechanisms of circadian control. Work in aromatase-deficient mice suggests that some sex differences in photic responsiveness are independent of gonadal hormone effects during development. In parallel, aspects of sex differences in sleep are also reported to be independent of gonadal steroids and may involve sex chromosome complement. This a summary of recent work illustrating how sex differences and gonadal hormones influence sleep and circadian rhythms that was presented at a Mini-Symposium at the 2011 annual meeting of the Society for Neuroscience.

https://www.jneurosci.org/content/jneuro/31/45/16107.full.pdf

Sleep, Rhythms, and the Endocrine Brain: Influence of Sex and Gonadal Hormones

The temporal ordering of physiological and pathological processes has always been of considerable interest to the biological scientist as well as to the clinician. How­ ever, the historical dominance of the concept of constancy of the "milieu interior" and biological homeostasis as formulated by Claude Bernard in France and Walter B. Cannon in the United States has directed most past research efforts in the direction of studying stimulus-response and steady-state mechanisms. During the past 25 years, however, the field of biological rhythms has made great strides and has emphasized that all singleand multicell organisms and a wide variety of biological functions within these organisms demonstrate endogenous oscillatory behavior. The disciplines of endocrinology and neuroendocrinology have been at the forefront of these issues because of the critical interface relationsips of the central and peripheral nervous system, endocrine secretory systems, and the blood circulat­ ing communicative pathway. During the past ten years there has been a major conceptual change emphasizing the rhythmic oscillatory and episodic temporal ordering of neuroendocrine events in relation to the 24-hr sleep-waking rhythm. The cross-fertilization of the disciplines of biological rhythms, sleep physiology, and neuroendocrinology has led to a series of important observations which have chal­ lenged 24-hr homeostatic and steady-state concepts. The use of the techniques of frequent serial blood sampling, sophisticated microchemical assay techniques, and polygraphic sleep stage analysis have allowed studies to be carried out in man correlating large numbers of sequential multiple hormone measurements with sleep­ waking functional states. The results of these studies have demonstrated that hor-

Circadian rhythms and episodic hormone secretion in man.

1. Daily fluctuations in the plasma concentrations of thyroid stimulating hormone (TSH) and growth hormone (GH) have been studied in six normal males by using a 24 h continuous blood-sampling technique and a highly sensitive and specific radioimmunoassay for TSH. 2. In all subjects the plasma concentrations of the two hormones were increased at night. The TSH concentrations rose approx. 2 h before the onset of sleep but the peak concentration coincided with the GH peak 2 h after the commencement of sleep. In three subjects who slept in the afternoon, additional peaks of GH activity were found and in two cases peaks of TSH activity also occurred. 3. The mean data from all subjects showed a significant circadian variation of TSH secretion with a maximum between 2 a.m. and 4 a.m. and a minimum between 6 p.m. and 8 p.m.

The 24-Hour Plasma Thyrotrophin Profile

The association of testosterone, sleep, and sexual function in men and women

IN man, several studies1,2 have demonstrated diurnal variation, with a morning peak, in plasma testosterone—the most potent naturally occurring androgen. The origin of this variation is not known.

Concentrations of Plasma Testosterone in Normal Men during Sleep

Plasma levels of testosterone have been found to show diurnal fluctuations with a morning peak (Dray et al. 1965, Resko & Eik-nes 1966). This peak was, however, lost when regular periods of sleep and activity were disturbed (Nieschlag & Ismail 1970), and suggested a connexion between sleep and plasma testosterone levels. Sleep consists of two fundamental physiological states which alternate regularly (Oswald 1962). Four or five cycles of orthodox sleep (slow wave sleep), each occupying approximately 60-90 min, occupy 75% of total sleep. In orthodox sleep, the EEG is dominated by slow waves and some fast frequencies the sleep spindles and most physiological parameters decline towards basal levels. Eye movements and mental activity

D. Love

Papers

Concentrations of Plasma Testosterone in Normal Men during Sleep

Circulating levels of plasma testosterone during sleep.