Seasonal Changes of Plasma Estradiol and Progesterone in the Japanese Monkey (Macaca fuscata fuscata)

Abstract

The plasma levels of estradiol and progesterone in 5 mature female Japanese monkeys (M. fuscata fuscata) throughout a breeding and nonbreeding season were measured by radioimmunoassay. As the breeding season approached, plasma estradiol levels started to increase, and a few elevations were detected. Neither a plasma progesterone rise nor menstrual bleeding was seen. Menstrual bleeding began in Dec. and recurred regularly 4 or 5 times at 4 wk intervals until April. During this period, cyclic estradiol elevations (150-250 pg/ml) and luteal progesterone rises (2.0-5.3 ng/ml) were observed. After the last menstruation in March or April, 2 animals showed an estradiol elevation, but progesterone levels remained in the basal range, and amenorrhea persisted. Female Japanese monkeys apparently ovulate 4 or 5 times a year, i.e., their breeding season is definitely defined. The changes of both steroids in transitional periods between nonbreeding and breeding, and breeding and nonbreeding seasons, suggested that some follicle development occurred in these periods. The elucidation of the mechanisms involved in the seasonal variation of reproductive functions in the Japanese monkey may provide useful information concerning some aspects of amenorrhea in human females.