PERIPHERAL PLASMA LEVELS OF OESTRONE, OESTRADIOL-17β AND PROGESTERONE DURING OVULATORY MENSTRUAL CYCLES IN THE RHESUS MONKEY WITH SPECIAL REFERENCE TO THE ONSET OF MENSTRUATION

Abstract

ABSTRACT The levels of oestrone (E1)*, oestradiol-17β (E2) and progesterone (P) were determined simultaneously by radioimmunoassay in serial peripheral plasma samples from 11 rhesus monkeys (Macaca mulatta) during ovulatory menstrual cycles. In 3 other monkeys luteectomy was performed on day 20 or 21 of the menstrual cycle. The mean plasma levels of oestradiol-17β predominated over the mean E1 during the follicular phase, but during the luteal phase the E1 and E2 patterns varied widely. Before menstruation, increased or unchanged levels of E1 and E2 were mostly found. The decrease found in a few monkeys never reached the low levels found during the days after the midcycle peak. The plasma levels of progesterone increased from less than 0.2 ng/ml during the follicular phase to maximal values within 3 to 4 days after the midcycle peak of oestradiol-17β. The plasma levels of progesterone decreased to less than 1 ng/ml and remained low for 3 to 5 days before menstruation. In the luteectomized monkeys the plasma levels of P, E1 and E2 fell dramatically within 24 h and vaginal bleeding was detected within 72 h post-operatively. In 2 of the 3 luteectomized monkeys the levels of E1 and E2 increased before the bleeding. The ratio of oestrogens (oestradiol-17β and oestrone) over progesterone changed markedly in favour of the oestrogens during the pre-menstrual period. It is concluded that the patterns of progesterone and oestrogens are divergent during the luteal phase. The maximal levels of progesterone are reached early while the maximal levels of oestrogens are reached later during the luteal phase.