Production of progesterone from de novo-synthesized cholesterol in cumulus cells and its physiological role during meiotic resumption of porcine oocytes. Biol Reprod 2003; 68:1193–1198

To investigate the role of factors secreted by cumulus cells during meiotic resumption of porcine oocytes, 1, 5, 10, or 20 cumulus-oocyte complexes (COCs) were cultured in each well of a culture dish containing 300 ml of maturation medium for 20 h. There was a significant positive correlation between the rate of germinal vesicle breakdown (GVBD) and the number of COCs cultured in each well for 20 h. The level of progesterone in the medium in which COCs had been cultured for 20 h also rose significantly with an increase in the number of COCs cul-tured in each well. A significantly small proportion of GVBD in oocytes when one COC was cultured in each well for 20 h was improved by the addition of progesterone. This proportion of GVBD was fully comparable to that of COCs cultured in the absence of additional progesterone with 20 COCs. Thus, pro-gesterone secreted by COCs plays a positive role in GVBD in-duction in porcine oocytes. Furthermore, we also examined the role of sterol biosynthesis on progesterone production by cu-mulus cells and in oocyte GVBD. The results showed that the addition of ketoconazole, which suppressed the sterol biosyn-thetic pathway produced by demethylation of lanosterol, de-creased the rate of GVBD, as well as progesterone production in COCs cultured for 20 h. However, the suppression of GVBD by ketoconazole was overtaken by the addition of progesterone. These results demonstrate that a high level of progesterone pro-duced by cumulus cells was responsible for an acceleration of GVBD in porcine oocytes. cumulus cells, gamete biology, meiosis, ovum, progesteron