Effects of systemic administration of indomethacin to cyclic ewes on endometrial concentrations of prostaglandins effects on estrous cycle length and on progesterone, luteinizing hormone and prolactin patterns.

Experiments were designed to evaluate in cyclic sheep the effects of systemic administration of a prostaglandin synthetase inhibitor (Indomethacin). Indomethacin (100 mg, 3 times daily, S.C.) was administered from day 7 of the estrous cycle for 16 days to five ewes in which the cycle was synchronized as well as the cycles of five control ewes. All control ewes had cycles of approximately 17 days duration, but three of five Indomethacin treated ewes showed no estrous behavior before their slaughter at 23 days after induced ovulation. Autopsy revealed normal corpora lutea which had not undergone luteolysis, as confirmed by progesterone determination in blood. The two remaining Indomethacin treated ewes showed an estrous behavior on day 19 and 20 respectively together with a "preovulatory surge" of luteinizing hormone and prolactin which was not followed by follicular rupture. These results show that inhibition of PGF2 alpha synthesis by systemic administration of Indomethacin to the ewe is able to prevent luteolysis. When luteolysis did occur however, it was not followed by an ovulation despite a normal gonadotropin surge, indicating that inhibition of prostaglandin synthesis by systemic administration of Indomethacin interferes with the luteolysis and follicle rupture processes.