Dynamics of periovulatory steroidogenesis in the rhesus monkey follicle after ovarian stimulation

The temporal relationships and regulation of events in the primate follicle during the periovulatory interval are poorly understood. This study was designed to elucidate the dynamics of steroid synthesis in the macaque follicle during ovarian stimulation cycles in which serum/follicular fluid aspirates were collected at precise intervals before (0 h) and after (up to 36 h) administration of the ovulatory human chorionic gonadotrophin (HCG) bolus. Serum concentrations of progesterone increased (P < 0.05) within 30 min, and follicular fluid progesterone concentrations were elevated 180-fold within 12 h, of HCG injection, and remained elevated until the time of ovulation. In contrast, 17β-oestradiol concentrations increased initially, but then declined (P < 0.05) by 36 h post-HCG. Acute incubation of granulosa cells with and without steroidogenic substrates demonstrated that: (i) 3β-hydroxysteroid dehydrogenase and aromatase activities were present in equivalent amounts before and after HCG; whereas (ii) P450 side-chain cleavage activity increased (P < 0.05) within 12 h of HCG; and (iii) exogenous low-density lipoprotein and cholesterol were not utilized for steroidogenesis. This model should be useful for further studies on ovulation and luteinization in primates, and enable elucidation of the local actions of progesterone and other steroids at specific time points during the periovulatory interval.