Induction by PGF2a of 20alpha-hydroxysteroid dehydrogenase in first generation corpora lutea of the rat

20alpha-Hydroxysteroid dehydrogenase (20alpha-OH-SDH) activity was determined in the first generation corpora lutea from prepubertal rats injected with 10 I.U. of pregnant mare's serum gonadotrophin (PMSG) on day 30. The enzyme was not detectable in 1-9-day-old corpora lutea but a significant activity was seen on day 10. Enzyme activity increased during day 11 and day 12. In vivo administration of prostaglandin F2a (PGF2a) induced the enzyme in rats with corpora lutea older than 3 days. When prolactin was given concurrently with PGF2a, the corpus luteum activity of 20alpha-OH-SDH was lower than when PGF2a was given alone. It is concluded that the present "corpus luteum model" is suitable for further analysis of the cellular mechanisms of the luteolytic effect of prostaglandins (PGs) as well as of the role of gonadotrophins in the luteolytic process.