PLASMA GONADOTROPINS, PROLACTIN, GONADAL-STEROIDS, AND GENITAL SWELLING DURING THE MENSTRUAL-CYCLE OF LOWLAND GORILLAS

Plasma LH [lutropin] FSH [follitropin], PRL [prolactin] 17.beta.-estradiol [E2], progesterone [P] and testosterone [T] were measured during 4 menstrual cycles in 3 gorillas and their relationship to genital swelling (labial tumescence) was assessed as a contribution to the comparative perspective on primate reproductive physiology. Cycle length varied considerably (23-48 days), but the length of the luteal phase was relatively constant (11-13 days). All cycles exhibited a midcycle LH peak (25.9-48.1 mIU/ml) and a luteal phase elevation in P (10.8-12.2 ng/ml), suggesting normal ovulatory function. FSH increased at midcycle but not as consistently as LH. PRL showed no rhythmicity. E2 showed a midcycle elevation (200-500 pg/ml) that preceded the LH peak and a luteal phase elevation that approximated the time course of P. P was barely detectable during the follicular phase (< 0.5 ng/ml), rose on the day of the LH peak (n = 2) or a day later (n = 2), peaked 6-7 days after the LH peak, and decreased to low levels at menses. T exhibited a midcycle peak of 350-500 pg/ml compared to follicular and luteal phase values (150-300 pg/ml). Labial tumescence was minimal at menses (1-2 cm), rose after 6-16 days, and reached maximum (3-4 cm) 9-35 days after menses on the day before the LH peak (n = 4) in association with the midcycle elevation in E2. Detumescence occurred 0-3 days after the LH peak, when E2 was decreasing and P was increasing. The gorilla shares with the chimpanzee a somewhat closer relationship to man than do the monkeys with respect to certain aspects of the menstrual cycle hormone patterns studied.