[The effect of progesterone and RU486 on progesterone production in the ovulatory process of rats].

To clarify the autoregulatory mechanism of progesterone (P) production in the ovulatory process, we examined the ovarian concentration of P 46 hrs after PMSG and the effects of P and RU486 (RU) injected 4-2 hrs before hCG administration on the serum concentrations of P and estradiol (E2), and ovarian 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activities in PMSG/hCG treated immature rats. The effect of RU on the number of ovulated ova was also studied. The ovarian concentration of P 46 hrs after PMSG was 0.96 +/- 0.03,ng/mg protein (mean +/- SEM). When P (100,mg/kg) was injected 2 hrs before hCG, ovarian 3 beta-HSD activities had significantly increased by 4 hrs after hCG. However, P at a dosage of 10 and 20,mg/kg had no effect on ovarian 3 beta-HSD activities. The administration of RU (20,mg/kg) 2 hrs before hCG significantly inhibited ovarian 3 beta-HSD activities measured 4 and 6 hrs after hCG (p less than 0.01 and p less than 0.05, respectively). In addition, the serum P concentration 4 hrs after hCG was significantly lower than that of the control (p less than 0.01). However, RU (20 mg/kg) in concomitant with hCG had no effect on ovarian 3 beta-HSD activities within 6 hrs after hCG. The suppression of ovarian 3 beta-HSD activities by RU was the concomitant reversed by the concomitant treatment with P (10 mg/kg). RU (10, 20, or 40 mg/kg) injected 2 hrs before hCG significantly reduced the number of ovulated ova (p less than 0.01, p less than 0.01 and p less than 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)