Evidence of progesterone dependence in ovulation induced by human chorionic gonadotropin in female rabbits.

The ovulation rate at 14 hours after human chorionic gonadotropin (hCG) injection in female rabbits was significantly reduced and the postovulatory increase in progesterone levels in peripheral and ovarian veins were suppressed by four days sulpiride-induced hyperprolactinemia, as compared to the control group. However, the levels of estradiol and testosterone from the same samples showed comparable alterations between the control and sulpiride-treated rabbits. When progesterone was added to hCG to induce ovulation in sulpiride-primed animals, the ovulation rate was restored as compared to the control group. These results suggest that progesterone is a prerequisite for ovulation in this experimental system.