Increased progesterone secretion and 3 beta-hydroxysteroid dehydrogenase activity in human cumulus cells by pregnenolone is limited to the high steroidogenic active cumuli.

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Several reports imply that lower progesterone secretion by cumulus-oocyte complexes (COCs) is associated with lower fertilization in the corresponding oocyte. The possible role of progesterone in oocyte fertilization in humans was studied using two approaches: (a) increasing the total progesterone secretion by culturing more than one COC per dish; and (b) increasing the cumulus cell progesterone secretion by providing pregnenolone as a substrate. Mature COCs were cultured individually or cocultured in groups. Oocyte fertilization and progesterone secretion were tested after 20 hr and 3 days in culture, respectively. The cumuli from individually plated COCs were cultured in the absence of oocyte for an additional 3 days in order to test the effects of pregnenolone on progesterone secretion and the 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity. A comparable study with pregnenolone was performed on the corresponding granulosa-lutein cells. Increasing the number of COC to two instead of one led to a significant increase in both fertilization rate and progesterone secretion. The addition of pregnenolone during days 3-6 increased significantly both progesterone secretion and 3 beta-HSD activity. Comparable results were observed in granulosa-lutein cells subjected to pregnenolone treatment. Following the first 3 days culture, cumulus masses were categorized as secreting high or low progesterone levels. Adding pregnenolone had a greater effect on both progesterone secretion and 3 beta-HSD activity in the high-progesterone-secreting cumuli. Addition of pregnenolone increased progesterone secretion and 3 beta-HSD more efficiently in the higher-progesterone-secreting cumuli. Coculture of two COCs instead of one led to a higher fertilization rate and greater progesterone secretion.