Potential role for lipoxygenase products of arachidonic acid in prostaglandin F2 alpha-stimulated oxytocin release from the ovine corpus luteum.

Intrauterine administration of nordihydroguaiaretic acid (NDGA) will maintain luteal function in sheep and also suppress the release of both oxytocin and prostaglandin F2 alpha (PGF2 alpha) suggesting that 5-lipoxygenase products of arachidonic acid may be involved in ovine luteolysis. During luteolysis, uterine PGF2 alpha is considered to be the major stimulus for the secretion of luteal oxytocin, and we report the effects of 5-lipoxygenase inhibition, via intrauterine NDGA administration, on the ability of PGF2 alpha to effect such secretion. In the NDGA-treated ewes, luteal function was maintained and oestrus delayed, the duration of the oestrous cycle (20 +/- 1 days; mean +/- S.D.; n = 9) being significantly (P < 0.01) longer than in intact controls (15 +/- 1 days, n = 4). Jugular infusions of PGF2 alpha did not stimulate luteal secretion of oxytocin, the effects being comparable with those in ovariectomized ewes. In intact ewes receiving intrauterine infusions of vehicle only, PGF2 alpha produced marked increases in luteal secretion of oxytocin. Also, preinfusion or basal concentrations of oxytocin in this group of ewes (6.6 +/- 1.9 pg/ml) were significantly (P < 0.01) greater than in either the NDGA-treated (3.1 +/- 1.1 pg/ml) or ovariectomized (3.0 +/- 0.6 pg/ml) ewes. The results suggest involvement of 5-lipoxygenase products of arachidonic acid in the release of oxytocin from the ovine corpus luteum.