Abstract
The functional role of the cumulus oophorus during fertilization was examined. It was found that the sperm concentration necessary for successful fertilization was markedly different between cumulus-intact and cumulus-free oocytes; only 5 sperm/μl were required for the maxi-mum level of fertilization of cumulus-intact oocytes, while 150 sperm/μl were needed for cumu-lus-free oocytes. Fertilization rate did not increase by co-culturing cumulus-free oocytes with detached cumulus cells in the fertilization medium. On the other hand, supplementing the fertili-zation medium with soluble factor(s) vortexed out of cumulus-oocyte complexes significantly improved the rate of fertilization (56% in the treated group vs 36% in controls; P<0.05) when spermatozoa were preincubated in BSA-supplemented medium. No significant effect, however, was observed when spermatozoa were preincubated in protein-free medium. These results strongly suggest that soluble factor(s) sustained in cumulus-oocyte complexes promote fertilization, and the integrity of the three dimensional structure of the cumulus oophorus is important for efficient sperm-egg interaction.
