Progesterone and 20alpha-hydroxysteroid-dehydrogenase regulation in the corpus luteum of the pregnant rat.

Female Wistar rats were mated and passively immunized against bovine luteinizing hormone (bLH) between days 7-12 of gestation. In a first series of experiments the effect of simultaneous progesterone treatment on the histochemically detectable activity of 20alpha-hydroxysteroiddehydrogenase (20alpha-OHSD) in the corpora lutea of pregnancy was evaluated. In other experiments the exact time course was established between the first histologically demonstrable signs of termination of pregnancy and the appearance of 20alpha-OHSD activity in corpora lutea of pregnancy. It was found that progesterone substitution not only prevented the deleterious effects of the anti-bLH-serum on gestation but also the re-appearance of 20alpha-OHSD activity in the corpora lutea of pregnancy up to day 12 of pregnancy. Moreover in animals injected with anti-bLH-serum from day 7 on and sacrificed on days 8-12, signs of foetal destruction clearly preceded the pathological re-appearance of 20alpha-OHSD activity by 2-3 days. These results support previous findings on a direct or indirct role of progesterone in the complex regulation of 20alpha-OHSD activity. Possible mechanisms of action are discussed.