Role of Arachidonic Acid and Its Metabolites in the Regulation of Progesterone and Oxytocin Release from the Bovine Corpus Luteum

Abstract

We have examined the effects of arachidonic acid (AA) and some of its metabolites on progesterone (P₄) and oxytocin (OT) release by corpora lutea obtained from Holstein heifers at day 8 of the estrous cycle (Day 0 = estrus). The luteal cells were dispersed with collagenase and small and large cells were separated by unit gravity sedimentation and flow cytometry. After an 18-hr preincubation period, the cells were incubated in the presence of various treatments for 1 hr, followed by a 23-hr incubation period with no treatment. OT was secreted by the large, but not by the small, luteal cells into the incubation medium. AA elicited a significant (P < 0.05) release of OT from the large cells and P₄ from both the large and small cells within 1 hr of incubation, having a specific effect at a concentration of 10 μM. Larger doses (25 and 100 μM) of AA adversely affected the cell viability. Phospholipases A₂ (0.5 unit/ml) and C (0.05 unit/ml) and calcium ionophore A23187 (0.1 μM) stimulated OT release from the large cells to the same extent as AA (10 μM). Inhibition of the AA cyclooxygenase metabolic pathway by indomethacin did not affect AA-induced release of OT and P₄, although exogenous prostaglandins F_2α and I₂ (5–25 ng/ml) stimulated the release of OT. Lipoxygenase products of AA (hydroxyeicosatetraenoic acid and leukotrienes; 25 ng/ml) also stimulated OT release. Inhibition of the lipoxygenase metabolic pathway by nordihydroguaiaretic acid abolished AA-induced release of both OT and P₄. These results suggest that intracellular accumulation of free AA may modulate secretory functions in the bovine corpora lutea, including OT and P₄ release.