Involvement of Lipoxygenase Products of Arachidonic Acid Metabolism in Bovine Luteal Function

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Abstract
A series of experiments was conducted to determine the effects of lipoxygenase products of arachidonic acid (AA) metabolism on the function of the bovine corpus luteum (CL). In the first experiment, reaction products of soybean lipoxidase-AA were added to dispersed bovine luteal cells in increasing concentrations. These lipoxygenase products resulted in a dose-related reduction in the biosynthesis of progesterone and 6-keto-prostaglandin (PG)F1.alpha., while the synthesis of (PG)F2.alpha. was unaffected. In a second experiment, the addition of 5-hydroxyeicosatetraenoic acid (5-HETE), a specific lipoxygenase product, again resulted in a reduction in progesterone and 6-keto-PGF1.alpha., with no change in PGF2.alpha. synthesis. Extremely high endogenous concentrations of 5-HETE were measured in luteal tissues (36 .+-. 17 to 46 .+-. 13 ng/106 cells) in a third experiment. In the fourth experiment, an inhibitor of the lipoxygenase pathways, nordihydroguaiaretic acid (NDGA) infused into the uterine lumen twice daily on Days 14-18 of the estrous cycle delayed luteolysis and resulted in lengthened estrous cycles (27.2 .+-. 0.3 vs. 21.5 .+-. 1.0 days for controls, p < 0.05). Thus, an inhibitor of the lipoxygenase pathway of arachidonic acid metabolism delays luteolysis, possibly by removing the preferential inhibition of PGF1.alpha. biosynthesis caused by 5-HETE and other products of the lipoxygenase system. Collectively, these results suggest that products of the lipoxygenase pathway are involved in luteolysis in normal heifers.