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

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Abstract
The endocrine characteristics of the menstrual cycle were determined in 16 Assamese monkeys (M. assamensis). Average cycle length was 32 .+-. 2 (.+-. SEM [standard error of the mean]) days which was divided into a 16 .+-. 1 day follicular phase and a 16 .+-. 1 day luteal phase. LH [luteinizing hormone, lutropin] and FSH [follicle-stimulating hormone, follitropin] 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 .mu.g/ml (mean .+-. SEM) and FSH from 3 .+-. 1 to 9 .+-. 1 .mu.g/ml. Estrogens increased at midcycle from 275 .+-. 75 to 432 .+-. 89 pg/ml. Progesterone rose from < 0.5 ng/ml during the follicular phase to between 2-4 ng/ml 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. Apparently, the Assamese monkey can serve as an appropriate model for the study of primate reproductive physiology.