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Radioimmunoassays were used for the measurement of several androgens in canine plasma and in the liquid of the vas deferens. Large variations in the plasma concentrations of androstenedione, testosterone and 5α-dihydrotestosterone occurred during a period of 24 h, but there was no evidence of a circadian rhythm. The ratios of the androgen concentration in the liquid of the vas deferens compared with that in the peripheral plasma were: androstenedione, 4·6; testosterone, 1·9; 5α-dihydrotestosterone, 13·6; 5α-androstane-3α,17β-diol, 17·0; 5α-androstane-3β,17β-diol, 22·4. These high levels of androgens in the liquid of the vas deferens could play a role in the development of prostatic hypertrophy.
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It is now well established that several hormones are secreted in an episodic or pulsatile fashion (McNatty, Cashmore & Young, 1972; Murray & Corker, 1973). When plasma concentrations of certain hormones are examined, peaks occur at intervals related to different features of the 24-h cycle, circadian rhythms (Retiene, Zimmerman, Schindler, Neuenschwander & Lipscomb, 1968). Circadian and episodic patterns in thyroid function have been claimed by certain workers (Bakke & Lawrence, 1965; Blum, Greenspan & Magnum, 1968) and refuted by others (Schatz & Volpe, 1959; Odell, Wilber & Utiger, 1967). A partial explanation of these conflicting results probably lies in functional differences in the level of the hypothalamo-pituitary-thyroidal-peripheral target tissue axis under investigation by different techniques.
Five Jersey bull calves aged between 2 and 80 days were investigated on a total of nine occasions. Five experiments were conducted under natural lighting conditions (daylight from 04.30 to 19.30 h). Calves in the
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Recent studies of the circadian rhythm of steroidal and gonadotrophic hormones (Hellman, Nakada, Curti, Weitzman, Kream, Roffwarg, Ellman, Fukushima & Gallagher, 1970; Katongole, Naftolin & Short, 1971; Sederberg, Binder & Kehlet, 1971; Naftolin, Yen & Tsai, 1972) have shown that it is far from being the smooth diurnal variation usually reported. Instead rapid fluctuations in the levels of the hormones occur throughout the day. The present study was undertaken to confirm the findings of Naftolin et al. (1972) regarding luteinizing hormone (LH) and to attempt to correlate the plasma levels of LH with changes in plasma testosterone. Blood samples (5 ml) were obtained at 10-min intervals over an 8-h period, between 09.00 and 17.00 h, from three normal men. The men (aged 25–30 years) were recumbent throughout the experiment, except when urinating, and were awake and allowed to read or converse. Frequent sampling was facilitated by the use of an
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The steroid 11-oxygenation index (i.e. the ratio of the urinary metabolites of cortisol precursors to those of cortisol) has been used by Hill (1960) and by Edwards, Makin & Barratt (1964) in the diagnosis of congenital adrenal hyperplasia. Both showed that any circadian variations in the index were small compared with the gross abnormalities encountered in this condition. In the course of physiological studies on temperature and renal excretory circadian rhythms we have observed a small but definite circadian variation in the steroid 11-oxygenation index in normal men.
Six male subjects (ages ranging from 21 to 55 yr.) followed a routine consisting of rest, light activity, feeding and drinking, which was repeated every 90 min. during a 27 hr. experiment. Urine was collected for 3 hr. periods and the 11-deoxy and 11-oxy 17-hydroxycorticosteroids (11-deoxy and 11-oxy 17-OHCS) were separately estimated (Few, 1968) in each sample. The steroid 11-oxygenation index was
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It is well-known that adrenocortical secretory activity shows a characteristic oscillating course with a 24-h period. This is promoted by a corresponding circadian rhythm of corticotrophin (ACTH) secretion, normally related to the alteration of sleep with the waking state. In the urine, this phenomenon is expressed by a urinary steroid flow which rises during the morning hours reaching a maximum between 08.00 and 12.00 h and subsequently drops to its lowest level at about 24.00 h. It is thus possible to assess the effects on the adrenal cortex of a strictly physiological corticotrophic stimulus such as that to which the adrenal cortex is subjected during the early morning hours (Ceresa, Angeli, Boccuzzi et al. 1969, 1970). In fact, any qualitative change induced by endogenous ACTH in adrenal steroid secretory activity may be detected at the urinary level by variations of the metabolic pattern.
The present investigation was done in 16
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Biological oscillations with an endogenous period of near 24 h (circadian rhythms) are generated by the master circadian pacemaker or clock located in the suprachiasmatic nuclei (SCN) of the hypothalamus. This clock is synchronised to recurring environmental signals conveyed by selective neural pathways. One of the main chemical constituents of SCN neurones is vasoactive intestinal polypeptide (VIP). Such neurones are retinorecipient and activated by light. Exogenous application of VIP resets the SCN circadian clock in a light-like manner, both in vivo and in vitro. These resetting actions appear to be mediated through the VPAC2 receptor (a type of receptor for VIP). Unexpectedly, genetically ablating expression of the VPAC2 receptor renders the circadian clock arrhythmic at the molecular, neurophysiological and behavioural levels. These findings indicate that this intrinsic neuropeptide acting through the VPAC2 receptor participates in both resetting to light and maintenance of ongoing rhythmicity of the SCN.
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Ovariectomized rats in which <7% of the suprachiasmatic nuclei had been spared by bilateral radiofrequency lesions were distinguishable from those with >40% of the nuclei by their consistent failure to show the oestrogen-induced daily surge of LH, either with or without pharmacological manipulations of serotonin (5-HT), and also by their loss of the normal rhythmicity of drinking. Minor damage to structures adjacent to the suprachiasmatic nuclei was similar in both groups. The identical facility with which electrical stimulation of the preoptic area induced LH release in the two groups of animals suggested that they were not characterized by different degrees of damage to the preopticotuberal pathway. These results are considered in relation to evidence indicating that the suprachiasmatic nuclei represent the densest concentration of 5-HT terminals in the forebrain and also the site of a mechanism involved in the generation of circadian rhythms.
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The occurrence of circadian variations in the concentration of prolactin in the plasma of 6- to 9-month-old male rats has been assessed in animals exposed to light for 14 h/day (lights on 06.00–20.00 h). Blood samples were obtained after decapitation, or from individual rats at regular intervals via a permanent cannula. Care was taken to limit stress during sampling. The concentration of prolactin in the plasma was significantly lower between 07.00 and 15.00 h than at other times. Between 15.00 and 20.00 h (during the light period), the concentration of prolactin was significantly higher in comparison with the preceding period, or with the remainder of the 24 h period. During the night, the concentration fluctuated, probably because of episodic releases of the hormone. The possible physiological significance of a circadian rhythm in the plasma concentration of prolactin and the implications for endocrine experimentation are discussed briefly.
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Department of Animal Science and Production, University of Western Australia, Nedlands, Western Australia 6009, Australia
(Received 13 March 1978)
The activity of the adrenal gland is believed to be governed by the secretion of corticotrophin (ACTH) in a positive stimulus/negative feedback equilibrium. There is increasing evidence that in man, the secretion of corticosteroids never actually reaches a steady-state condition and that the circadian rhythm displayed by these hormones in the circulation is therefore the result of a number of secretory episodes over a 24 h period (Hellman, Nakada, Curti, Weitzman, Kream, Roffwarg, Ellman, Fukushima & Gallagher, 1970; Weitzman, Fukushima, Nogeire, Roffwarg, Gallagher & Hellman, 1971). Data presented by McNatty, Cashmore & Young (1972) also raise the possibility that a similar pattern of hormone release may exist in the sheep. However, McNatty et al. (1972) collected samples relatively infrequently and it is hard to define peaks in cortisol concentration. With more
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Circadian changes in plasma 18-hydroxy-11-deoxycorticosterone (18-OH-DOC), total and unbound cortisol were studied in four groups: seven healthy young men, six elderly men, six elderly women and six elderly demented patients of both sexes. The daily activities of the subjects were synchronous; blood samples were taken every 4 h and 4 hourly urine samples were collected only from the young men. A circadian rhythm was defined for plasma 18-OH-DOC, total and unbound cortisol in all groups; the secretory patterns of these steroids were parallel, as were the profiles of urinary 18-OH-DOC and unconjugated cortisol. When compared with respect to sex, the 24-h mean level of total cortisol was higher in women; that of unbound cortisol was higher in the three groups of elderly patients than in the young men. No major changes in plasma steroids were observed between elderly demented patients (mainly women) and healthy elderly women. The phasing of total and unbound cortisol showed no major modifications with age, sex or senile dementia. Acrophases of 18-OH-DOC were earlier in elderly patients than in young men. Amplitudes were not modified with sex in elderly patients but were always lower in the demented patients. A circadian rhythm was defined for 18-OH-DOC, unconjugated cortisol, 17-hydroxycorticosteroids (17-OH-CS) and 17-ketosteroids in the urine of the young men. The acrophases of 18-OH-DOC and unbound cortisol were close, as were those of 17-OH-CS and 17-ketosteroids. The lag was short between the acrophases of 18-OH-DOC in plasma and urine and between those of plasma unbound cortisol and urinary unconjugated cortisol; it was much larger between the acrophases of plasma total cortisol and 17-OH-CS.
Thus, the process of ageing, and the possible alterations in the central nervous system which are often seen in normal ageing, induced no major modifications in the temporal organization of adrenocortical function, even in subjects who were very advanced in age.
