The Plasma Pattern of Ovarian Steroids during the Menstrual Cycle in Capuchin Monkeys (Cebus apella)

Abstract

Daily plasma concentrations of estradiol and progesterone were determined during an entire menstrual cycle in 10 capuchin monkeys (Cebus apella). The mean length of the studied cycles was 21.0 ± 1.1 days. Estradiol levels were ∼70-100 pg/ml during the early follicular phase (Days 1-4). The levels increased to a midcycle peak of 503.3 ± 30.6 pg/ml occurring on Days 7-9 of the cycle. Thereafter, estradiol declined to minimal values (53.6 ± 5.1 pg/ml) on Day 5 postpeak. During the luteal phase there was no significant increase in estradiol levels. The plasma concentration of progesterone was relatively low (3-10 ng/ml) during the follicular phase. The first increase over previous values occurred on Day 1 after the estradiol peak and reached extremely high values (66.9 ± 5.6 ng/ml) on Day 6 postestradiol peak. Plasma progesterone concentrations fell rather abruptly, reaching the relatively low levels seen during the early part of the cycle, 1 day before the onset of menstruation. In 1 monkey with a presumptive anovulatory cycle the length of the cycle as well as the characteristics of the menstrual flow did not differ from those of monkeys with normal ovulatory cycles. In this animal an estradiol peak was not discernible, whereas progesterone levels showed an oscillating pattern at relatively low levels during the intermenstrual interval.