PLACENTAL 17-BETA-HYDROXYSTEROID OXIDOREDUCTASE, LACTATE-DEHYDROGENASE AND MALATE-DEHYDROGENASE DURING THE LATTER HALF OF PREGNANCY IN THE MOUSE

The specific activity of 17beta -hydroxysteroid oxidoreductase (17-HOR ) with estradiol-17beta (E2), estrone (E1) and testosterone (T), as we ll as that of lactate dehydrogenase (LDH) and malate dehydrogenase (MD H) were measured in homogenates of CF-1 mouse placenta during the latt er half of pregnancy. 17-HOR activity with E2 and T increased over 100 -fold between days 9 and 12, and 3- to 4-fold between days 15 and 19, with no further change to day 21. In contrast, activity with E1 increa sed 39-fold between days 9 and 12, 3.8-fold between days 15 and 19 but then decreased between days 19 and 21. The E2/T activity ratio was co nstant while the E2/E1 ratio increased between days 9 and 21. LDH incr eased 2-fold between days 9 and 12 with no further increase to day 19. MDH was constant from day 9 to 19. Activity with E2 was inhibited by T, 5alpha -dihydrotestosterone (5alpha-DHT) and DHA but not by E1, and rostenedione (A) or 20alpha-dihydroprogesterone. Activity with T was i nhibited by E2, 5alpha-DHT and DHA, but not by A. In contrast, activit y with E1 was inhibited by A and DHA but not by E2, T or 5alpha-DHT. T he results suggest placental 17-HOR is developmentally regulated. Alth ough the results are also suggestive of multiple forms of 17-HOR, a si ngle enzyme with an ordered kinetic mechanism cannot be ruled out.