[Dual action of prostaglandins in the regulation of HCG-induced ovulation in immature rats (author's transl)].

With the aid of indomethacin, a potent inhibitor of prostaglandin synthesis, the mechanism of action of prostaglandins on follicle rupture was studied. Mean number of ova shed following treatment of immature rats sequentially with PMS and hCG was reduced in a dose-dependent manner by simultaneous injection with increasing doses of indomethacin. The minimum effective dose to block ovulation completely was 90 micrograms. However, the anti-ovulatory action of the minimum effective dose at 0 h became progressively less potent as the time between hCG injection and indomethacin administration was increased. Another dose-dependent relationship was found 10 h after hCG injection, the closest time prior to the onset of ovulation, the minimum effective dose necessary to prevent ovulation was 8 times higher than at 0 h, suggesting that prostaglandins acted differently on ovulation in the later stage of the preovulatory process. It is concluded that prostaglandins may mediate the action of hCG on ovulation at least through two mechanisms.