Formation of 6-hydroxylated progesterone in the human placenta and response to hCG

The in vitro metabolism of 7alpha-3-H-pregnenolone by five term human placentas obtained from repeat cesarean section was studied. Incubations were carried out either with minced tissue for 1 h or by organ culture for 6 h and 24 h. Twenty-one experiments were performed to determine the effect of human chorionic gonadotropin (hCG), human placental lactogen (hPL), and heat-inactivated hCG on the metabolism of pregnenolone. The major radioactive product was progesterone (40-60%); unchanged pregnenolone accounted for only 5-15% of the radioactivity. 3-H-6beta-OH-progesterone was found and rigorously identified. In control experiments 6beta-OH-progesterone was 2-4% of the radioactivity. In the presence of hCG there was a significant (P smaller than 0.005) 2-3-fold increase of 3-H-6beta-OH-progesterone in the 1-h mince incubations and the 24-h organ cultures. There was no increase of 3-H-6beta-OH-progesterone over control values with hCG after 6-h organ cultures; with heat-inactivated hCG; or with hPL. These findings provide additional data that hCG affects steroid metabolism in the human placenta. In addition, 3-H-6alpha-OH-progesterone was found and rigorously identified in yields of approximately 0.5-1%. The effect of hCG on 6alpha-hydroxylation was not determined. This appears to be the first demonstration of 6alpha-hydroxylation of C21 steroids by human tissue.