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Prostaglandin E₂-9-Ketoreductase Activity of Preovulatory Ovine Follicles¹

University of Wyoming, Laramie 82071

Abstract

Enhanced accumulation of follicular PGF₂ with respect to PGE₂ during the later phase of the preovulatory period is an apparent prerequisite for ovulation in sheep. Prostaglandin (PG) E₂-9-ketoreductase is the enzyme that converts PGE₂ into PGF₂. Expression of activity of this enzyme by tissue homogenates of preovulatory ovine follicles was assessed. Homogenates were incubated in the presence of tritiated PGE₂. Prostaglandin F₂ (i.e., product) was separated from PGE₂ by Sephadex chromatography and quantitated by liquid scintillation counting. Progesterone in follicular fluid was measured by RIA. Follicular activity of PGE₂-9-ketoreductase and content of progesterone increased approximately sixfold as the time of ovulation approached. Formation of PGF₂ from PGE₂ was not influenced by inhibition of follicular synthesis of prostaglandins by indomethacin, nor did such treatment affect follicular production of progesterone. Inhibition of follicular synthesis of progesterone by isoxazol suppressed enzymatic conversion of PGE₂ into PGF₂; this effect was reversed by progesterone. It appears that progesterone plays an intrafollicular role in induction of activity of PGE₂-9-ketoreductase in sheep.

¹ Supported by NIH HD-19527 and NSF R11-8610680. We are indebted to C. J. Beaver and E. A. Van Kirk for their capable assistance in surgery and the laboratory.

² Reprint requests.

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