Biology of Reproduction, Vol 13, 408-414, Copyright © 1975 by Society for the Study of Reproduction

5-Reductive Pathway of Progesterone Metabolism in the Amphibian Ovarian Cytosol

¹ Departments of Pharmacology and Physiology Albert Einstein College of Medicine of Yeshiva University New York, New York 10461

The metabolism of ³H-progesterone by the 105,000 x g supernatant (cytosol) fraction of Rana pipiens follicles containing fully grown oocytes was studied using thin layer chromatography. At 18°C, progesterone was rapidly metabolized to products that co-migrated with and appeared in the sequence: pregnanedione, pregnanolone, and pregnanediol. The pregnanedione fraction appeared to consist primarily of the 5-stereoisomer. At 4°C, 50 percent of the progesterone was metabolized by the cytosol in 1-2 h compared to 15-20 min at 24°C. As a 3-keto-⁴ steroid target tissue the R. pipiens ovary appears to be unique in that both the 5 and 5 reduced isomers are nearly as effective as the parent compound (progesterone) in inducing a physiological response (germinal vesicle breakdown). Pregnanolone and pregnanediol were relatively ineffective in inducing germinal vesicle breakdown. Thus, the stepwise reduction of pregnanedione may terminate a steroid-specific action in the ovarian follicle.

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