Plasma Concentrations of Free 5α-Androstane-3α,17 β -diol and Related Gonadal Steroids During Spontaneous and Induced Sexual Maturation in the Female Rat

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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 10-fold 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, exogenous 3.alpha.-diol suppressed 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.

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