The Influence of Exogenous PMS and HCG on the Arachidonic Acid Content of the Immature Rat Ovary

Summary

The influence of exogenous PMS and/or HCG, on the arachidonic acid (C 20:4ω6) content of the immature rat ovary was examined. Changes in ovarian arachidonate content associated with hormone administration were assessed in total lipid extracts, and in several neutral and phospholipid fractions. Both relative percentage and absolute amounts of arachidonic acid in several lipids were measured as well as uptake of radioactivity into total lipid resulting from the administration of ³H-labeled arachidonic acid in vivo.

On the basis of these studies, we conclude (1) PMS, with or without HCG promotes increased uptake of exogenous arachidonic acid into ovarian total lipids; (2) Arachidonic acid is a major fatty acid constituent from noncholine containing phosphatides at the onset of normal estrous (ca. 38 days) even in the animals which received no PMS or HCG; (3) Changes in ovarian arachidonic acid levels following gonadotropin administration are more striking in the two phospholipid fractions than in the two neutral lipids examined; (4) PMS is associated with a rapid outpouring of ovarian lipid, accompanied by a high turnover of arachidonic acid which is enhanced or modified temporally by added HCG in vivo.

These results provide the first quantitative evidence that gonadotropins may regulate prostaglandin biosynthesis in the ovary by their effects on the uptake, storage, or release of arachidonic acid, a major PG precursor, from specific ovarian lipids. While the data strongly suggest that the regulation of one or more ovarian esterases (cholesterol esterase, lipase, phospholipase) is the mechanism by which gonadotropins regulate PG biosynthesis, a direct action on PG synthetase is not ruled out.

The authors wish to thank Doctor Robert H. Franklin for his helpful suggestions and assistance throughout the study.

This research was supported in part by USPHS Grant NB-4277 from the National Institute of Neurological Diseases and Blindness, the Moody Foundation, Galveston, Texas, and the South Carolina Appropriations for Research.