Plasminogen Activator Activity in Cumulus-Oocyte Complexes of Gonadotropin-Treated Rats during the Periovulatory Period1

Two types of plasminogen activator (tissue-type, tPA; urokinase-type, uPA) have been demonstrated in ovarian granulosa cells, but only tPA activity was found in denuded oocytes. Immature rats were treated subcutaneously with 20 IU pregnant mare’s serum gonadotropin (PMSG) to stimulate follicle maturation, followed 2 days later by an injection of 10 IU human chorionic gonadotropin (hCG) to induce ovulation. Cellular plasminogen activator activities were determined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis followed by a fibrin-overlay technique. Cumulus-oocyte complexes from rats before and after PMSG treatment contained low amounts of tPA, but not uPA, activity. After hCG treatment, tPA activity showed a time-dependent increase, reaching a maximum at 24 h after injection. At 12 and 24 h after hCG treatment, uPA activity was also detected. The appearance of high molecular weight lysis zones further suggested the formation of plasminogen activator-inhibitor complexes. Morphological analysis indicated that the increases in oocyte tPA activity were correlated with the extent of cumulus cell expansion and dispersion. In denuded oocytes, tPA activity also progressively increased during the periovulatory period to a maximum at 24 h after hCG treatment. In contrast, neither uPA activity nor activator-inhibitor complex was detected. Secretion of the proteases was measured in the conditioned media of cumulus-oocyte complexes cultured for 24 h in vitro. Substantial increases in tPA release were found in complexes obtained at 8 and 12 h after hCG injection, with lower secretion from complexes obtained at 24 h after hCG treatment. To examine hormonal responsiveness, cumulus-oocyte complexes were incubated with follicle-stimulating hormone (FSH) or hCG for 24 h, and the total (medium plus cell) tPA activity was determined. Tissue PA activity was markedly increased by both FSH and hCG in cumulus-oocyte complexes obtained from PMSG-treated, but not control, rats. After in vivo hCG treatment, the elevated basal tPA activity was not affected b y gonadotropins. Thus, gonadotropin stimulation of ovulation is associated with increased celluar content and secretion of tPA activity by the cumulus-oocyte complexes. The observed periovulatory changes in protease activity may be related tofollicle rupture or cumulus cell expansion and dispersion.