Relation between aggressive behaviour and circadian rhythms in cortisol and testosterone in social groups of talapoin monkeys.

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 animal's 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.(ABSTRACT TRUNCATED AT 250 WORDS)