Action of porcine follicular fluid oocyte maturation inhibitor in vitro: possible role of the cumulus cells.

To study the mode of action of porcine follicular fluid oocyte maturation inhibitor isolated cumulus-enclosed or mechanically denuded pig oocytes were used. Two types of culture media were employed, a complex containing 15% pig serum (TC199A) and a defined, minimal medium (BMOC). The maturation of cumulus-enclosed oocytes was comparable in the two types of culture media, but only in the complex medium did the cumulus cells remain functional in terms of morphology and progesterone secretion. The low molecular weight portion of follicular fluid partially inhibited oocyte meiosis and cumulus progesterone secretion in 199A. No inhibition of oocyte maturation was seen when follicular fluid was added to BMOC. Since denuded oocytes did not respond to follicular fluid in either culture medium, it is suggested that the cumulus cells may mediate the action of the follicular fluid oocyte maturation inhibitor.