Changes in Steroidogenesis in Preovulatory Rat Ovaries Induced to Ovulate with Pregnant Mare Serum Gonadotropin*

Publisher Website
Google Scholar
Abstract
The pattern of steroids produced by the immature rat ovary is different from that observed in the adult cycling rat. Changes in steroid production were studied several hours before the 1st ovulation, as it was anticipated that during this transitional period both the immature and mature pattern of steroid formation may coexist in the ovary. Ovarian homogenates (1000 .times. g supernatant) obtained from 26 day old rats treated 52 h previously with 25 IU PMSG [pregnant mares serum gonadotropin] were incubated in the presence of NADPH with either [14C]progesterone, 20.alpha.-[3H]hydroxy-4-pregnen-3-one (20.alpha.-OHP), or [14C]progesterone and 3.alpha.-[3H]hydroxy-5.alpha.-pregnan-20-one (5.alpha.P-3.alpha.-ol-20-one). The dose of PMSG used induces an endogenous LH [lutropin] surge in the afternoon of day 26, which is followed by ovulation. After incubation, radioactive metabolites were isolated, identified, and measured by TLC and GLC, with derivative formation and recrystallization to constant specific activity. 5.alpha.-Pregnane-3.alpha.,20.alpha.-diol (5.alpha.P-3.alpha.,20.alpha.-diol) and 5.alpha.-androstane-3.alpha.,17.beta.-diol (5.alpha.A-3.alpha.,17.beta.-diol) were the major products formed. 20.alpha.-OHP seems to be an intermediate product in the formation of 5.alpha.P-3.alpha.,20.alpha.-diol from progesterone because 1) [14C]20.alpha.-OHP was formed with [14C]progesterone served as substrate and 2) [3H]20.alpha.-OHP was readily converted into [3H]5.alpha.P-3.alpha.,20.alpha.-diol by the ovarian supernatant. 5.alpha.P-3.alpha.,20.alpha.-diol was also produced by reduction of 5.alpha.P-3.alpha.-ol-20-one; this was shown by double isotope experiments in which ovarian homogenates were incubated with both [14C]-progesterone and [3H]5.alpha.P-3.alpha.-ol-20-one. The 5.alpha.P-3.alpha.,20.alpha.-diol isolated was labeled with both isotopes. 5.alpha.P-3.alpha.,20.alpha.-Diol was not further metabolized when incubated for 90 min with the ovarian preparation. In an experiment in which a high concentration of [3H]5.alpha.P-3.alpha.-ol-20-one was added concomitantly with [14C]progesterone, no 14C label was found in 5.alpha.P-3.alpha.-ol-20-one isolated at the end of the experiment, while 3.alpha.,17.alpha.-dihydroxy-5.alpha.-pregnan-20-one (5.alpha.P-3.alpha.,17.alpha.-diol-20-one) was labeled with both isotopes. 5.alpha.P-3.alpha.,17.alpha.-diol-20-one was produced from progesterone through a 17.alpha.-hydroxylated intermediate. As 5.alpha.A-3.alpha.,17.beta.-diol in both double labeling experiments showed a 3H:14C ratio half of that observed in 5.alpha.P-3.alpha.-ol-20-one and in 5.alpha.P-3.alpha.,17.alpha.-diol-20-one, 5.alpha.A-3.alpha.,17.beta.-diol was also produced by a 3rd route, probably through ostenedione. Three possible pathways lead to 5.alpha.A-3.alpha.,17.beta.-diol formation in the ovarian preparation under investigation.

This publication has 0 references indexed in Scilit: