The effects of progesterone and RU486, a synthetic anti-progesterone, on ovarian 3β-hydroxysteroid dehydrogenase (3β-HSD) activity, a key enzyme of progesterone production, were studied during ovulation in immature 22-day-old rats primed with pregnant mares' serum gonadotrophin (PMSG) and human chorionic gonadotrophin (hCG). Ovarian 3β-HSD activities had increased significantly 4 h after hCG injection. These increases were inhibited at 4 and 6 h after hCG when 20 mg RU486 kg−1 was administered 2 h before hCG. However, RU486 had no influence on the activity of 3β-HSD when administered at the same time as hCG injection. A histochemical study revealed that 3β-HSD activities in the granulosa cell layer, but not in the theca cell layer, were inhibited when RU486 was given 2 h before hCG. Serum progesterone concentrations, but not oestradiol concentrations, were significantly suppressed by RU486 treatment 4 and 6 h after hCG. The effect of progesterone on ovarian 3β-HSD activity was tested by administering graded doses of progesterone exogenously to rats 2 h before hCG injection. Ovarian 3β-HSD activity was increased in a dose-dependent manner, and more than 20 mg progesterone kg−1 significantly stimulated the activity. Although 10 mg progesterone kg−1 did not stimulate ovarian 3β-HSD activities, the RU486-inhibited activities were recovered by the concomitant administration of 10 mg progesterone kg−1 with RU486. These results indicate that ovarian 3β-HSD activity depends on progesterone concentrations, and suggest an autocrine regulation of progesterone production during ovulation in immature rat ovaries stimulated with PMSG and hCG.
If the inline PDF is not rendering correctly, you can download the PDF file here.