Involvement of plasminogen activator activity in the process of ovulation

The present study was undertaken to determine the changes in follicular plasminogen activator (PA) activity during ovulation. In the first experiment, hCG (100 IU) administration in vivo enhanced PA activity in mature follicles within 1 hour. PA activity reached its maximum at 4 hours and then declined. A second peak occurred 8 hours after hCG administration. In the second experiment, the effects of an ovulatory dose (50 IU) of hCG on ovulatory efficiency and PA activity were assessed in mature and immature follicles with an in vitro perfused rabbit ovary preparation. Ovulatory efficiency in immature follicles was significantly less (p less than 0.01) (16.7 +/- 4.5%) than that in mature follicles (86.7 +/- 11.0%). During the perfusion, the growth of mature follicles was observed but not that of immature follicles. PA activity in mature follicles derived from unstimulated ovaries was 1.43 +/- 0.17 IU/g tissue. PA activity in mature follicles (28.4 +/- 4.2 IU/g tissue) 4 hours after in vitro exposure to hCG was significantly greater (p less than 0.01) than that found in immature follicles. In conclusion, exposure to gonadotropin stimulates PA activity in preovulatory follicles. Failure to increase PA activity in immature follicles impairs follicular development, resulting in reduced ovulatory efficiency. The increase in PA activity observed in ovulatory follicles implicates the plasmin-generating system in follicle rupture.