Endocrine Characteristics of the Menstrual Cycle in the Assamese Monkey (Macaca assamensis)

The endocrine characteristics of the menstrual cycle were determined in 16 Assamese monkeys (Macaca assamensis). Average cycle lengt.h was 32 ± 2 (± SEM) days which was divided into a 16 ± 1 day follicular phase and a 16 ± 1 day luteal phase. LH and FSH concentrations were fairly constant throughout the cycle except at midcycle when both gonadotropins surged. At this time LH concentrations increased from 4 ± 2 to 17 ± 4 ug/mI (mean ± SEM) and FSH from 3 ± 1 to 9 ± 1 ug/mI. Estrogens also increased at midcydle from 275 ± 75 to 432 ± 89 pg/mI. Progesterone rose from less than 0.5 ng/ml during the follicular phase to between 2 and 4 ng/mI during the luteal phase. Although there was variation between animals, the concentrations and patterns of these hormones were similar to those reported for other species of macaques. These results suggest that the Assamese monkey can serve as an appropriate model for the study of primate reproductive physiology.