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ABSTRACT

Circadian rhythms in cortisol and testosterone in both blood and cerebrospinal fluid (CSF) were studied in four groups of male and female talapoin monkeys. Samples were taken 4 h apart under two conditions: whilst the sexes were kept separate (isosexual) and again after 24 h of interaction (heterosexual). There were similar rhythms in cortisol in males and females during the isosexual condition, though in blood (but not in CSF) mean levels were higher in females. Heterosexual interaction increased cortisol levels in both sexes (though more so in males), and also altered the shape of the rhythm, acrophase being delayed by 4 h in males and by 2 h in females. The amplitude of the rhythm was not altered. Cortisol levels were positively correlated in both males and females with the amount of aggression received from other males, but not from females nor with the animals' social rank.

Circadian rhythms in serum testosterone in males were also altered by heterosexual interaction. Access to females delayed acrophase by 2 h, but had no effect on mean levels (unlike the effect on cortisol). As for cortisol, the amplitude of the testosterone rhythm remained unchanged. Serum testosterone was negatively correlated with aggression from males, but not from females nor with sexual interaction. This was associated with a pronounced decrease in the levels of testosterone during the night, not observed in males receiving no aggression from others. There was a non-significant trend towards a positive correlation between social rank and serum testosterone.

These results show that social behaviour in groupliving primates has major effects on the parameters of the circadian pattern of secretion of both cortisol and testosterone. Aggression received from males seems to be a potent factor associated with the daily rhythms in both hormones, though there may be rank-related effects in the case of testosterone.

J. Endocr. (1987) 115, 107–120

SUMMARY

The incorporation of [³⁵S]methionine into protein in various regions of the brain and in the anterior pituitary, and serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels were measured at 6 h intervals throughout a 24 h period in the following groups of Wistar rats: (1) normal adult males and females; (2) adult genetic males or females which had been respectively 'feminized' or 'masculinized' by androgen deprivation or administration in neonatal life. Similar measurements were made at 12 h intervals in adult male rats which had been castrated at 7 or 15 days of age.

Serum LH levels showed a circadian rhythmicity in normal adult animals of both sexes, with peak levels in the male occurring 6 h earlier than those in the female. There was no statistically significant circadian rhythm in FSH levels in any group of animals. In all groups of castrated animals LH and FSH levels were raised but no circadian rhythms were observed.

Incorporation of [³⁵S]methionine into protein in all cerebral areas showed circadian rhythms, the peak values of which, in the adult males, were almost 8 h (120°) out of phase with those of the adult females. In the 'feminized' genetic males or 'masculinized' genetic females the rhythmic phase was reversed to that of the opposite genetic sex. Animals castrated at 7 days or 15 days of age did not appear to show a rhythm.

A 12 h rhythm of incorporation was apparent in the anterior pituitary of the normal adult male and the adult 'masculinized' female; no significant rhythm was seen in the normal adult female and the 'feminized' male.

It is suggested that a 'female type' rhythm of incorporation in the brain may be associated with the maintenance of oestrous cycles.

Stimulation of the uterine cervix (CS) induced a nocturnal surge of prolactin at 04.00 h and a diurnal surge at 17.00 h in normal ovariectomized rats. However, the CS-induced prolactin surges did not occur in ovariectomized rats which had been treated with 250 μg testosterone propionate during the neonatal period. Chronic bilateral lesions of the suprachiasmatic nucleus (SCN) completely abolished the CS-induced nocturnal and diurnal surges of prolactin release which were observed in sham-lesioned, ovariectomized rats. Furthermore, bilateral lesions of the medial basal part of the suprachiasmatic area (MBSC), lying rostral to the SCN, were also effective in blocking the CS-induced nocturnal and diurnal surges. Lesions which destroyed mainly the optic chiasma and extended partially into the MBSC and SCN did not block the CS-induced prolactin surges.

These results suggest that one reason for the failure of ovary-grafted male rats and neonatally androgenized female rats to maintain pseudopregnancy is the extinction of the circadian rhythm of the two daily prolactin surges, and that the MBSC, in addition to the SCN which is known to be a generator of other circadian rhythms, is involved in generation of the rhythm of prolactin surges.

The circannual rhythms of plasma 18-hydroxy-11-deoxycorticosterone (18-OH-DOC), total and free cortisol have been documented on a circadian basis in January, March, June and October in seven young men (24 years old), six elderly men, six elderly women and six elderly demented subjects, both men and women, in their eighties. Blood samples were drawn every 4 h over a 24-h period at each sampling session and urine samples were collected at 4-h intervals only from the young men. A circadian rhythm of 17-hydroxycorticosteroids (17-OH-CS), 17-ketosteroids (17-KS), urinary free cortisol and 18-OH-DOC was defined for each of the four seasons with stable acrophases throughout the year and the same excretory profiles. A circannual rhythm was validated in young men for 17-OH-CS, urinary free cortisol and 18-OH-DOC but not for 17-KS. A circadian rhythm of plasma free cortisol, the active form of the hormone, plasma total cortisol and plasma 18-OH-DOC was validated in all groups and at all the seasons at which samples were taken. The secretory profiles of 18-OH-DOC, free and total cortisol were very similar, with no differences attributable to age, sex or mental condition except for the levels of plasma free cortisol and 18-OH-DOC which were higher and lower respectively in the elderly subjects. Whereas a circannual rhythm of plasma 18-OH-DOC was validated for all groups, a circannual rhythm of both free and total cortisol in the plasma was validated in young men but not in any group of elderly subjects. This loss of the circannual rhythmicity of cortisol in the elderly may reflect the decrease with age of the capacity to adapt to seasonal external factors.

ABSTRACT

The daily changes in rat thyroid calcitonin and its specific mRNA concentrations, and the relationship between their dynamics and the plasma levels of calcitonin, calcium and phosphate over a 24-h period were investigated. The circulating calcitonin concentration rose during the daily dark period when plasma calcium and phosphate levels were minimal, indicating that plasma calcitonin rhythm cannot be generated directly by a linear effect of calcium on hormone secretion. Moreover, we established that the expression of the calcitonin gene also exhibited periodic dynamics observable at the pretranslational level: the gland content of hybridizable specific calcitonin RNA displayed daily rhythms; specific RNA levels peaked during the light period and were minimal during the first part of the dark period. Significant changes in thyroid calcitonin concentrations also occurred over a 24-h period. Statistical analyses which distinguished between variations over the 24-h period and residual variations were performed to test the relationships between the various parameters. The daily rhythms of hybridizable RNA, thyroid calcitonin and plasma minerals appeared to be in phase, while the plasma calcitonin concentration displayed variations out of phase with these rhythms. The implication of the correlations observed on the residual variations is discussed in comparison with the temporal relationship between the daily variations. The results fit the hypothesis that hormone production and secretion are self-oscillating processes. Plasma concentrations of calcium and phosphate might play a role in the synchronization of the calcitonin metabolism periodicity.

Journal of Endocrinology (1989) 122, 527–534

SUMMARY

In the present study the circadian changes which occur in the levels of corticosterone in the brain and plasma in Sprague–Dawley rats are reported. The levels of corticosterone in the brain were found to have a daily trough and crest with timing similar to that observed for the plasma steroid. In addition, the effect of histamine stress on the corticosterone content of the particulate and the soluble fractions at the trough and crest was examined. The levels of both brain fractions were significantly higher 20 min after histamine injection. The time of day at which the stress was applied was not a significant factor in the magnitude of the stress response.