Effect of Pregnant Mare's Serum Gonadotrophin on the Activities of Δ4-5α-Reductase, Aromatase, and Other Enzymes in the Ovaries of Immature Rats

Abstract

After incubation of progesterone, 17.alpha.-hydroxyprogesterone, androstenedione and testosterone with an ovarian preparation (supernatant fluid at 10,000 .times. g) of immature rats (21-23 days of age) in the presence of NADPH, 3.alpha.- and 3.beta.-hydroxy-5.alpha.-reduced steroids were obtained as the major metabolites. Among the enzyme activities relevant to the metabolism, .DELTA.4-5.alpha.-reductase and 3.beta.-hydroxysteroid dehydrogenase were intracellularly localized to the microsomal fraction (10,000-105,000 .times. g), and 3.alpha.-hydroxysteroid dehydrogenase was detected exclusively in the cytosol fraction (supernatant fluid at 105,000 .times. g). Within 2 days after a single injection of pregnant mare''s serum gonadotropin (10 IU/rat) to 21 day old female rats, the following occurred: an enhancement of 17.alpha.-hydroxylase and C-17-C-20 lyase activities; a suppression of .DELTA.4-5.alpha.-reductase activity; and an increase in aromatizing activity. The increased secretion of estrogen from ovaries of immature rats stimulated by pregnant mare''s serum gonadotropin administration was caused by a modification of the ovarian enzyme activities relevant to estrogen production.