The relationship between progestins and gonadotropins during the late luteal phase of the menstrual cycle in rhesus monkeys.

Abstract

The effects of progesterone on blood levels of FSH and LH during the late luteal and early follicular phase of the cycle were studied in 10 regular cycling rhesus monkeys. Progesterone administered for 8 days in silastic capsules, beginning 12 days after peak concentrations of estrogen in serum, prolonged the luteal phase levels of this hormone in 6 animals. Blood levels of progesterone were not affected in 4 control animals given cholesterol. Throughout two consecutive cycles, progesterone, 20α-hydroxypregn- 4-ene-3-one, estradiol, FSH, and LH were measured by radioimmunoassay at selected intervals. The length of time between the LH peaks in cycle I and II differed significantly (p < 0.05) between animals treated with progesterone (35.8 ± 1.21, SD, days) and those treated with cholesterol (31.0 ± 2.16, SD, days). The concentrations of FSH in the late luteal and early follicular phase of the cycle continued to rise significantly (p < 0.01 by regression analysis) in both treated and control animals in spit...