Lipoxygenase metabolites of arachidonic acid in the porcine ovulatory process

It is widely accepted that prostaglandins (PGs), produced via the cyclooxygenase pathway from arachidonic acid, are essential to the ovulatory process in the pig. In support of this, ovulation is preceded by an increase in follicular fluid (FF) PG concentration, indomethacin (INDO) suppresses both the PG increase and ovulation, and ovulation can be restored by administration of exogenous PGs (Downey and Ainsworth, 1980; Prostaglandins 19: 17-22). Recent studies in the rat have shown that ovulation is also preceded by a rise in ovarian concentrations of 15-hydroxyeicosatetraenoic acid (15-HETE), a product of the lipoxygenase pathway (Tanaka et al., 1989; Endocrinology 15: 1373-1377) and inhibition of this pathway suppresses ovulation (Reich et al., 1983; Prostaglandins 26: 1011-1020). Furthermore, INDO, a cyclooxygenase inhibitor, inhibits 15-lipoxygenase as well as PG synthesis (Tanaka et al., 1989 Endocrinology 15: 1373-1377). The PMSG/hCG prepuberal gilt model was used to investigate the involvement of 15-HETE in the procine ovulatory process, and the effect of INDO on the 15-lipoxygenase pathway. Follicular fluid concentrations of 15-HETE were elevated 40 h post hCG (p $<$ 0.01). The effects of INDO and nordihydroguaiaretic acid (NDGA), an inhibitor of lipoxygenase activity, on ovulation rate, FF 15-HETE and FF PGF$ rm sb{2a}$ were investigated by intraovarian administration of INDO or NDGA. INDO inhibited ovulation rate (p $<$ 0.01) and PGF$ rm sb{2a}$ (p $<$ 0.01) as well as 15-HETE (p $<$ 0.01). NDGA also suppressed ovulation rate (p $<$ 0.01) but did not inhibit 15-HETE or PGF$ rm sb{2a}$ production. In in vitro experiments, 15-HETE production by both granulosa cell (GC) and theca interna cell (TIC) cultures 40 h post hCG was greater (p $<$ 0.01) than at 0 h post hCG. INDO inhibited 15-HETE production in 40 h post hCG TIC cultures (p $<$ 0.01) but not GC cultures, while NDGA inhibited 15-HETE production by both cell types (p $<$ 0.01). These results sugge