Zona-opening of hamster oocytes: a comparative study using macro- and micro-manipulation methods

The present study compared a new macro-manipulation technique for zona-opening of hamster oocytes with existing micro-manipulation techniques. In experiment I the zona pellucida of hamster oocytes was partially opened with a 32 gauge steel needle (macro-manipulation) and these oocytes were then co-incubated with human spermatozoa at 36.5 degrees C in 5% CO2 in air for 3.5 h. Zona-free and zona-intact oocytes similarly inseminated served as controls. Of 113 oocytes, 30 (26%) lysed following zona-opening with the macro technique. The sperm penetration rates of zona-opened and zona-free oocytes were 37% (31/83) and 60% (49/81) respectively (P < 0.01), with 12 and 28% oocytes respectively showing polyspermia (P < 0.05). No sperm penetration occurred in zona-intact oocytes. In experiment II the zona pellucida of hamster oocytes was partially opened by macro- or micro-manipulation techniques before the oocytes were coincubated with human spermatozoa as in experiment I. Nine of 156 (6%) macro-manipulated and 11 of 133 (8%) micro-manipulated oocytes lysed following zona-opening. Of 147 remaining macro-manipulated and 122 remaining micro-manipulated oocytes, 80 (55%) and 79 (64%) respectively were penetrated (P > 0.05), with 30 and 37% respectively showing polyspermia (P > 0.05). These results demonstrate that macro-manipulation results in similar penetration and polyspermia rates as compared to conventional micro-manipulation.