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Increase in Ovarian 15-Hydroxyeicosatetraenoic Acid during Ovulation in the Gonadotropin-Primed Immature Rat^*

NOBUYUKI TANAKA, LAWRENCE L. ESPEY and HITOSHI OKAMURA

Department of Biology, Trinity University San Antonio, Texas 78284
the Department of Obstetrics and Gynecology, Kumamoto University Medical School Kumamoto 860, Japan

Address requests for reprints to: Dr. Lawrence Espey, Biology Department, Trinity University, San Antonio, Texas 78284.

Abstract

The ovarian level of 15-hydroxyeicosatetraenoic acid (15-HETE) was measured by RIA during ovulation in gonadotropin-primed immature Wistar rats. The ovulatory process was initiated in 25-day-old rats by a 10-IU injection of hCG sc 2 days after the animals had been primed with 10 IU PMSG, sc. Ovarian follicles begin to ovulate 10 h after hCG. At 0 h after hCG, the ovarian 15-HETE level was 0.6 ± 0.2 ng/mg ovarian protein. At 6 h the 15-HETE level increased sharply to 27.3 ± 4.2 ng/mg protein and reached a peak of 50.0 ± 9.8 ng/mg protein at 10 h. Ovarian 15-HETE decreased significantly between 10-16 h after hCG (when ovulation was essentially completed). The pattern of secretion of this 15-lipoxygenase product was reciprocal to the pattern of secretion of leukotriene-B₄ by the rat ovary. Ovarian 15-HETE production and ovulation were inhibited in a dose-dependent manner when indomethacin was administered sc 1 h after hCG in doses ranging from 0.10-10.0 mg/rat. In contrast, the synthesis of ovarian prostaglandins-E and -F was inhibited by a dose of indomethacin as low as 0.0316 mg/rat, but this dose did not significantly affect the ovarian 15- HETE level or the ovulation rate. Therefore, the ovulation rate was more closely correlated with the ovarian 15-HETE level (P < 0.001) than with the ovarian levels of either prostaglandin-E or -F (0.10 > P > 0.05). The results suggest that products of the 15-lipoxygenase pathway of arachidonic acid metabolism may be important in the biochemical events of mammalian ovulation.

Footnotes

^* This work was supported by the Lalor Foundation and NIH Grants HD-21649 (to Trinity University) and HD-10202 (to the Center for Research in Reproductive Biology, Department of Obstetrics and Gynecology, University of Texas Health Science Center at San Antonio).

Postdoctoral fellow of the Lalor Foundation.

Received May 5, 1989.

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