Suppression of oxytocin-induced prostaglandin F2α release after intra-uterine nordihydroguariaretic acid administration in ewes.

Intrauterine administration of the 5-lipoxygenase inhibitor nordihydroguariaretic acid (NDGA; 5 mg, bid) on Days 9–14 of the ovine estrous cycle (estrus = Day 0) delayed luteolysis and extended the duration of the estrous cycle (20 ± 1, SD, vs. 16 ± 1 days; P < 0.01). In control ewes, plasma concentrations of 13,14,dihydro-15-keto prostaglandin F2α increased significantly (P < 0.001) following i.v. administration of oxytocin (10 i.u.) on Day 14; in the nordihydroguariaretic acid-treated ewes, however, there was no such increase. In addition, concentrations of endometrial oxytocin receptors were significantly less (P < 0.01) in the nordihydroguariaretic acid-treated ewes (218 ± 60 vs. 579 ± 66 fmol/mg tissue). These results suggest that 5-lipoxygenase products of arachidonate metabolism may be involved in the control of ovine luteal function.