Effects of arachidonic acid and oxytocin on equine endometrial PGF 2α during normal cycles and pseudopregnancy

Abstract

The effect of excess arachidonic acid or oxytocin on equine endometrial prostaglandin F 2α (PGF 2α ) synthesis was measured in vitro under physiologic and pathophysiologic conditions. Endometrial tissues obtained by uterine biopsy at 5, 10, 12, 14, 16 and 20 days post-ovulation from cycling mares, after 0, 2, 4, 6, 8, 10, 12, 14 or 16 days of progesterone (P 4 ) in ovariectomized mares and at 30 days postovulation in mares undergoing spontaneously prolonged corpus luteum (SPCL) activity were incubated in vitro with and without added arachidonic acid or oxytocin. Endometrial PGF 2α content and synthetic capacities were determined by radioimmunoassay. PGF 2α production increased significantly at Days 12–16. Arachidonic acid did not alter this effect. Oxytocin stimulated additional PGF 2α production on Days 5, 16, and 20. SPCL tissues had minimal PGF 2α production which was increased significantly by arachidonic acid but not oxytocin. PGF 2α synthesis in ovariectomized P 4 treated mares was minimal and did not vary with length of progesterone exposure or addition of arachidonic acid. These results suggest that a) oxytocin may play a role in luteolysis in the equine, b) although arachidonic acid appears not to be limiting to PGF 2 α production under normal physiological conditions, its absence may play a role in pathophysiological conditions, c) factors in addition to progesterone and arachidonic acid are required to initiate PGF 2α synthesis in the mare.