Blockade of spontaneous and LH-induced ovulation in rats by indomethacin,an inhibitor of prostaglandin biosynthesis

Indomethacin, an inhibitor of prostaglandin synthesis, blocks ovulation in immature rats pre-treated with pregnant mare serum gonadotropin (PMS), when given either at 0800, 1200 or 1600 hours on the second day after PMS treatment (the equivalent of proestrus in normally cycling adult rats). The drug also blocked ovulation in response to exogenous luteinizing hormone, whether the latter was administered 30 minutes before or 30 minutes after the inhibitor. Luteinization of follicles, and signs of pre-ovulatory progesterone secretion (loss of uterine lumen fluid) were not prevented when the inhibitor was given at 1600 hours, or when exogenous LH was administered in addition to the inhibitor, indicating that the luteinizing and steroidogenesis actions of LH upon the ovary were not completely blocked. When the drug was administered before the “critical period” for LH secretion, follicular luteinization and signs of progesterone secretion were also prevented, suggesting an additional action of indomethacin at the level of the hypothalamic-pituitary axis, inhibiting LH secretion.