Artificial menstrual cycles, behaviour and the role of androgens in female rhesus monkeys

Abstract

THE sexual behaviour of higher primates has special relevance to the human situation. The rhesus monkey, for instance, has a true menstruation, and copulation occurs throughout the cycle. Levels of sexual activity, however, are generally higher in the peri-ovulatory period¹, and a similar mid-cycle maximum has been reported for certain human couples². Androgens increase the sexual behaviour of rhesus females^3,4, and they have been used to treat loss of libido in women⁵. These observations, together with the rise in plasma testosterone near mid-cycle, have led to suggestions that androgens may be the main libidinal hormone in the female⁶. We report here our experiments to test this hypothesis. We devised a daily dose schedule of oestradiol, testosterone and progesterone for ovariectomised rhesus monkeys that duplicated the changing plasma levels during normal menstrual cycles. When males were paired with females so treated, sexual activity showed a pattern similar to that during the normal cycle, and the omission of testosterone was without any detectable effect on this pattern.