Sociosexual and hormonal changes in aging female bonnet macaques.

A comparison of younger mature and older perimenopausal female bonnet macaques showed differences in sexual interaction with males. Older females evoked significantly fewer copulations than did younger females. Although older females were cycling regularly, the midcycle (estrus) peaking of sexual interaction and levels of plasma estradiol were less pronounced in older than in younger females. Younger females were mounted more during estrus than during the luteal phase of their cycles, and the frequency of ejaculations and duration of intromissions were significantly greater during estrus. These cycle-phase differences were not observed with older females. The results suggest that aging in the female macaque is associated with reduction in sexual attractiveness to males. The possibility that changes in female proceptivity and receptivity contribute to this effect remains to be investigated.

Psychoendocrine correlates of sociosexual responsivity in older premenopausal primates.

Cycling older premenopausal female bonnet macaques (17 to 18 years) show decreased attractivity (mounting indices) and responsivity to males in short-term pair-testing compared to younger, fully mature cycling females (9 to 13 years). Comparison of age-group mean circulating levels of estrogen, progesterone, and testosterone during four phases of the menstrual cycle shows a significant decrement in older females only in the height of the estrogen surge during the periovulatory (estrous) phase of the cycle. Supplementation of older females with an estradiol + testosterone preparation (Deladumone, Squibb) did not restore behavioral sexual interaction to the level of younger females. The data suggest a gradual decline in sexual responsivity or arousal in older females which precedes the major endocrine changes of menopause. Such a lowering of responsivity appears comparable to that observed in aging (albeit sexually functional) human males.