| Abstract: | The method of in vitro fertilization was applied to test a previous suggestion that the lowered fertilizability of the tubal oocytes of female KE strain mice and the high resistance of their zona pellucida to proteolytic enzymes, are due to the premature cortical reaction taking place near the time of ovulation. Therefore higher fertilizability of ovarian oocytes is expected. The effectiveness of F1 hybrid sperm penetration into ovarian and tubal KE oocytes confirmed these assumptions. The ovarian KE oocytes recovered 9–10 hours after administration of human chorionic gonadotropin (HCG) showed significantly higher penetrability (70–83%) than did the tubal oocytes recovered 12 hours after HCG (about 50%) and 14–16 hours after HCG (20%). Similar results were obtained with C57 oocytes. Sperm penetration into ovarian oocytes (10 hours after HCG) was much more effective (67%) than into tubal oocytes (18%); this finding correlated with more rapid zona dissolution by chymotrypsin. On the basis of these results one might speculate that premature cortical reaction takes place also in the C57 strain. |
