Menstrual cycle of the baboon. I. Clinical features, vaginal cytology and endometrial histology.

Abstract

Ovulation in 4 sexually mature baboons was identified by gross examination of the ovaries at laporotomy by biopsy and histologic examination of the corpus luteum and by endometrial histologic and daily vaginal cytologic studies. At least 2 of the baboons had conceived previously. 18 endometrial biopsies were performed by hysterotomy throughout the menstrual cycle. For each vaginal smear the maturation index was calculated. The average length of the cycles of these 4 baboons was 32.7 plus or minus 3.2 days with a range of 28-40 days. The proliferative phase was judged to be 16.4 plus or minus 3.7 days. In all cycles the average duration of menstruation was 3.7 days with a range from 2-7 days based on gross vaginal bleeding. For each baboon the period of maximum turgescence varied from 3-10 days. Deturgescence occurred rapidly and the earliest day of deturgescence correlated positively with the day of ovulation. The vaginal cytology could be classified by daily changes in mucus and cell types and was similar to the vaginal cycle in women. There were no erythrocytes in the vagina at ovulation as there may be in women and the maturation index dropped more rapidly in baboons than in women in the secretory phase of the cycle. Vaginal smears may not always detect the exact day of ovulation in baboons but can provide evidence of anovulatory cycles. The endometrial cycle divided into 8 phases and the histologic changes closely resembled those found in women. Deturgescence was related to the hormonal changes accompanying ovulation which was also correlated with maturational indices of the vaginal smear.