Progesterone Biosynthesis and Metabolism by Ovarian Follicles and Isolated Oocytes of Xenopus laevis

Abstract

Ovarian follicles of X. laevis exposed to exogenous radioactive pregnenolone were observed to synthesize radioactive progesterone. Biochemical evidence demonstrates that the .DELTA.5-3.beta.-hydroxysteroid oxidoreductase activity is solely localized in the follicular envelopes. Cyanoketone inhibits human chorionic gonadotropin induced maturation and also pregnenolone-induced maturation. Evidences are presented which strongly suggest that the conversion of pregnenolone to progesterone is a prerequisite for biological activity. Progesterone and related steroids are actively metabolized by the ovarian follicle and also by the isolated (after collagenase treatment) oocyte. The results demonstrate that the defolliculated oocyte possess a 17.alpha.-hydroxylase, a C21-19 desmolase, a 20.alpha.-hydroxysteroid oxidoreductase and 5.beta./.alpha.-reductases. The 2 main metabolites isolated, after exposure to progesterone, from the oocyte are androstenedione and 17.alpha.,20.alpha.-dihydroxy-pregn-4-ene-3-one.