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B. J. EVERITT and J. HERBERT

SUMMARY

The effect of dexamethasone, given either alone or together with testosterone propionate or androstenedione, was studied in nine female rhesus monkeys (paired with three males) by making quantitative observations on behaviour in the laboratory.

Dexamethasone (0·5 mg/kg/day) given to oestrogen-treated ovariectomized female monkeys made them sexually unreceptive, and there was an associated decline in the level of the male's mounting activity. Testosterone propionate (100 or 200 μg/day) reversed completely the effects of dexamethasone on sexual behaviour. Androstenedione (100, 200 or 400 μg/day) had similar, but less marked, effects whereas cortisol (10 mg/day) or progesterone (100, 200 or 500 μg/day) were ineffective. Treating a female with testosterone prevented dexamethasone from reducing sexual receptivity. Parallel determinations of urinary free cortisol showed that the dexamethasone had suppressed the secretory activity of the adrenal cortex. There were no consistent changes, under any treatment, in the females' vaginal epithelia, sexual skins or clitorides, or in their water or electrolyte metabolism.

These findings indicate that adrenal androgens regulate sexual receptivity in these female primates, probably by an action on the central nervous system.

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N. D. Martensz and B. J. Everitt

Active immunization of an ovariectomized rhesus monkey against testosterone-3-(O-carboxymethyl)oxime–bovine serum albumin produced an antiserum with a high degree of specificity towards testosterone. Passive immunization of ovariectomized, oestrogen-treated monkeys with this antiserum resulted in significant reductions in proceptive and/or receptive behaviours in the majority of animals. This effect could be reversed by treatment with 17α-methyltestosterone, a steroid which showed only 6% cross-reaction with the antiserum. Passive immunization caused an increase in the binding of testosterone by the γ-globulin fraction of serum isolated by treatment with 2-ethoxy-6,9-diaminoacridine lactate. The present findings emphasize the importance of androgens of adrenal origin in the regulation of sexual behaviour in the female rhesus monkey.

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M. D. Stoneham, B. J. Everitt, S. Hansen, S. L. Lightman and K. Todd

ABSTRACT

In male New Zealand white rabbits, it was shown that oxytocin but not vasopressin concentrations in plasma were markedly raised after ejaculation. In male Wistar rats, oxytocin infused into the internal carotid artery reduced the number of intromissions made before ejaculation but had no other significant effect. Infusion of oxytocin into the third ventricle increased the latencies to the first mount and intromission and lengthened post-ejaculatory refractory periods. It is suggested that oxytocin released into the periphery during coitus, while not essentially involved in ejaculation, may exert effects on the genital periphery. Behavioural effects of centrally administered oxytocin suggest that it may play a role in the neural mechanisms underlying post-ejaculatory refractoriness.

J. Endocr. (1985) 107, 97–106

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N. D. Martensz, S. V. Vellucci, L. M. Fuller, B. J. Everitt, E. B. Keverne and J. Herbert

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