AJP - Endocrinology and Metabolism, Vol 240, Issue 5 489-E492, Copyright © 1981 by American Physiological Society
Differential effects of progesterone on secretion of gonadotropic hormones in the rhesus monkey
J. A. Resko, W. E. Ellinwood and E. Knobil
To obtain new information on the site of the inhibiting actions of
progesterone (P) during the follicular phase of the cycle, we administered
P continuously to 13 rhesus macaques (Macaca mulatta) from days 5 through
12 of the menstrual cycle. This treatment produced luteal-phase levels
(approximately 6 ng/ml of serum) within 4 h. (FSH) concentrations dropped
significantly from pretreatment amounts (P less than 0.01). During this
time, both immunoreactive luteinizing hormone (LH) (n = 8 animals) and
bioactive LH (n = 5) remained stable. The 17 beta-estradiol (E2)
concentrations dropped significantly below base line 24 h after treatment
(P less than 0.05). The decline in E2 occurred after the decline in FSH.
Inhibition of FSH continued for 40 h, after which both FSH and LH rose
steadily in a way that resembled a preovulatory surge on days 8 or 9 of the
menstrual cycle, and then returned to base line by day 10. When
gonadotropins were at their zenith, the ovary did not respond by secreting
E2. None of the effects mentioned above were found in control animals
treated with blank implants. These data demonstrate that P administered
during the follicular phase inhibits FSH but not LH secretion. This initial
inhibition probably occurs at a hypothalamic-pituitary site, but after 40 h
direct inhibitory effects on the ovary cannot be ruled out. P stimulates
the release of gonadotropin in female monkeys despite reduced production of
E2 by the ovary.
