Sperm‐egg interaction in immature hamster oocytes

Abstract

Abstract Immature oocytes were recovered from ovarian follicles at 0, 2, 4, 6, 8 and 10 hours after an ovulating injection of HCG. The envelopes (cumulus, corona cells and zona pellucida) of these oocytes were removed by enzymic treatment. The naked oocytes were incubated in vitro with capacitated spermatozoa to study the rate of sperm entry. A close correlation existed between the appearance of the ability of the oocyte to effectively interact with capacitated spermatozoa and the stage of nuclear maturation. The lowest percentage of sperm entry into zona‐free oocytes was observed at zero and two hours after the HCG injection. The nuclei of these oocytes were at the germinal vesicle stage and early first meiotic metaphase respectively. A significant increase in the rate of sperm entry was observed in oocytes recovered four hours after the HCG injection. The nuclei of these oocytes were still at the first meiotic metaphase. Percentages of sperm entry similar to controls were observed in oocytes recovered 6, 8 and 10 hours after the HCG injection. Germinal vesicle breakdown and a delay period for nuclear and cytoplasmic materials to interact, seem to be two important factors before gamete fusion can take place.