Inhibitory effect of homologous solubilized zona pellucida on rabbit in vitro fertilization

Rabbit zonae pellucidae were isolated using a modified technique of Dunbar et al. (1980). Zonae pellucidae were solubilized in saline phosphate buffer (pH 7.8) for 30 min at 70 degrees C. One dimensional SDS-PAGE analysis showed that zona pellucida is essentially composed of three major proteins with apparent molecular weights of 200 (275-165) kd, 100 (135-96) kd and 75 (96-51) kd. Preincubation of sperm with heat-solubilized zonae pellucidae (SZP) (5 to 8 SZP/microliters) did not reduce sperm binding ability. By contrast, it significantly decreased the percentage of penetrated eggs (20 versus 73% for the control) and significantly reduced the fertilization rate (10 versus 55% for the control). Ultrastructural analysis of several oocytes in the two groups demonstrated that inhibition of fertilization was not due to the inhibition of sperm-zona binding ability but essentially resulted from the impairment of sperm penetration through the zona pellucida.