Human spermatozoa attach to trypsin-treated hamster zonae pellucidae but do not undergo acrosome reactions.

The acrosome reaction by spermatozoa is an indispensable prerequisite for fertilization, and zonae pellucidae of human oocytes induce this reaction in the human spermatozoa attached to them. Human spermatozoa can attach to the zona pellucida of hamster oocytes when the oocytes have been treated with trypsin. We examined whether or not trypsin-treated hamster zona pellucida induces the acrosome reaction of human spermatozoa. Ten semen samples from 7 donors of proven fertility were examined in the present study. Highly motile spermatozoa were obtained by a swim-up method, and pre-incubated for 1 or 6 hours in modified Biggers, Whitten and Whittingham's (mBWW) medium supplemented with human serum albumin. The spermatozoa were then co-incubated for 1 hour with trypsin-treated hamster oocytes to allow sperm attachment to the zona. The spermatozoa on the zona were incubated for 3 additional hours in the mBWW medium. The percentage of acrosome reacted spermatozoa (%AR) was determined before and after the 3-hours of incubation. The %AR in the sperm suspension was also determined. There was no significant difference in the %AR between the spermatozoa attached to the zona pellucida and those in suspension during the incubation for 3 hours. These results indicate that the trypsin-treated hamster zona pellucida does not induce the acrosome reaction of human spermatozoa.