Effects of oestradiol on steroid dehydrogenase activities in rat corpora lutea

The activities of 20alpha-hydroxysteroid dehydrogenase and 3beta-hydroxysteroid dehydrogenase in rat corpora lutea during the second half of pregnancy were measured. In luteal tissue of the intact pregnant rat, 20alpha-hydroxysteroid dehydrogenase activity was undetectable between days 12 and 18 of pregnancy but appeared slowly after hypophysectomy and hysterectomy on day 12. Treatment of the hypophysectomized and hysterectomized animal with oestradiol delayed this increase until day 17, at which time a rapid induction of this enzyme occurred. In the normal pregnant rat mean luteal 3beta-hydroxysteroid dehydrogenase activity increased between days 12 and 18 (P less than 0.05, Student's t-test) but fell rapidly after hypophysectomy and hysterectomy on day 12. Oestradiol treatment prevented this fall in activity and enzyme activity was not distinguishable from that of the intact rat. Progesterone secretion correlated well with the activities of these two enzymes in the three conditions examined.