Periovulatory steroid concentrations in HCG-treated rabbits.

The level of pregnenolone increased within 1 h and remained high for 4 h after an intravenous injection of HCG in conscious rabbits. Peaks for progesterone, estrogens and dehydroepiandrosterone were recorded at 2 h, and that of 20alpha-dihydroprogesterone 6 h after HCG injection. At the time of ovulation the serum concentrations of all steroids had returned to their basal levels. It seems that HCG maintained a high production of pregnenolone and promoted the synthesis of different steroids.