The development of placental androstenedione and testosterone production and their utilization by the ovary for aromatization to estrogen during rat pregnancy.

During rat pregnancy the placenta may provide androgens as a source of precursor for estradiol (E2) formation by the ovary. However, the relative importance of testosterone (T) and delta 4-androstenedione (delta 4 A) for ovarian E2 production is unknown. The present study therefore determined the ability of the rat placenta to convert [3H] pregnenolone (P5) substrate to [3H] delta 4 A and [3H] T, and to [3H] progesterone (P4) in vitro on Days 12, 14, 16 and 18 of gestation. The placental formation of delta 4 A and T was correlated with the uterine vein and peripheral sera concentrations of both androgens, and with their ability to be aromatized to E2 in vitro by the ovary. Placental androgen formation from P5 increased and formation of P4 decreased with advancing gestation, with the formation of delta 4 A being approximately 2- to 4-fold greater (P less than 0.01) than the formation of T on Days 12 to 16 of gestation. The conversion of P5 to delta 4 A increased (P less than 0.001) from 18 +/- 0.9 (mean percent conversion +/- SEM) on Day 12 to 53 +/- 3 and 57 +/- 4 on Days 14 and 16, respectively, then decreased (P less than 0.05) to 42 +/- 2 on Day 18. The uterine vein and peripheral sera concentrations of delta 4 A were 2- and 3-fold greater (P less than 0.05-0.001) than T, respectively, on Days 12 to 16.(ABSTRACT TRUNCATED AT 250 WORDS)