[Effects of agents used for removal of zona pellucida on human sperm penetration into zona-free hamster egg].

In 1976, Yanagimachi et al. suggested that human sperm were capable of penetrating zona-free hamster eggs. Since that time, this in vitro penetration assay has been used to analyze human spermatozoal fertilizing ability. In the present study, effects of proteinases and S-S reducing agents used for removal of zona pellucida on human sperm penetration into zona-free hamster eggs were investigated. 0.1% trypsin, 0.05% pronase, 0.1% alpha-chymotrypsin and 300 IU/ml Dispase were proteinases used for this experiment, and 0.05 M mercaptoethanol and 0.025 M dithiothreitol (DDT) were S-S reducing agents. Results obtained were as follows: 1) When hamster eggs were treated for 3 minutes by these agents, percentages of eggs penetrated were 76.4% (trypsin), 75.6% (mercaptoethanol), 64.7% (alpha-chymotrypsin), 63% (pronase), 61% (Dispase) and 25.9% (DTT). 2) When hamster eggs were treated for 20 minutes, the figures were 83% (mercaptoethanol), 75.7% (trypsin), 63% (Dispase) 54% (pronase), 51% (alpha-chymotrypsin) and 13% (DTT). 3) There was no difference between human sperm penetration rates into zona-free hamster eggs treated for 3 minutes and those treated for 20 minutes. These results suggest that trypsin and mercaptoethanol were very useful agents for removing zona pellucida of hamster eggs in this in vitro fertilization system.