To elucidate the possible roles of increased plasminogen activator (PA) in follicular rupture and to investigate whether prostaglandins participate in ovarian PA synthesis in vivo, enzyme activities were sequentially measured by a method using the chromogenic substrate S-2251 in immature rat ovaries primed with pregnant mare serum gonadotrophin (PMSG) followed by human chorionic gonadotrophin (hCG) either alone or with a concurrent injection of indomethacin.
Before hCG injection PA activity was 0·006 ± 0·006 (s.d.) μmol/1·6 mg ovarian tissue (wet wt) per 30 min: PA activity of a saline-treated group remained at low levels (<0·018 ± 0·003 μmol/1·6 mg tissue per 30 min). In contrast, PA activity of animals given hCG alone increased after the treatment, reaching a peak value of 0·112 ± 0·071 μmol/1·6 mg tissue per 30 min 12 h later, before decreasing to 0·023 ± 0·014 μmol/1·6 mg tissue per 30 min at 32 h. Contrary to expectations, a dose of indomethacin which completely blocked ovulation had no effect on either the magnitude or the time-course of PA synthesis after hCG administration (P>0·05).
These results indicate that prostaglandins are not involved in the preovulatory synthesis of PA induced by hCG in rat ovaries and that PA is not a primary proteolytic enzyme for follicular rupture. It is suggested that PA has possible roles in cumulus detachment and/or proliferation of granulosa cells during the ovulatory process.
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