Plasma concentrations of free 5 alpha-androstane-3 alpha, 17 beta-diol and related gonadal steroids during spontaneous and induced sexual maturation in the female rat

Abstract

Plasma concentrations of free 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol), 5 alpha-androstane-3 beta, 17 beta-diol (3 beta-diol), 5 alpha-dihydrotestosterone (DHT) and of testosterone (T) were determined in female rats undergoing spontaneous sexual maturation or pregnant mare's serum gonadotropin (PMSG)-induced precocious ovulation. In the prepubertal period, 3 alpha-diol levels showed an inverse relationship with uterine weights and a significant drop between Days 21 and 26 of life. Postpubertally, 3 alpha-diol concentrations tended to rise again, to a lesser degree, in parallel with increments in plasma T. Concentrations of 3 alpha-diol were increased tenfold 48 h after the administration of PMSG, i.e., at a time when T and estradiol-17 beta also peaked. Concentrations of 3 beta-diol and DHT remained low throughout both experiments. In earlier studies, it was found that exogenous 3 alpha-diol suppresses reproductive function in the immature rat, but the high concentrations of endogenous 3 alpha-diol reported here for the PMSG model clearly do not interfere with ovulation. The observed constellations of plasma steroids are compatible with the postulate of a peripubertal shift in ovarian progesterone metabolism from 5 alpha-reduced C21 steroids to delta 4-3-ketosteroids.