Evidence for the involvement of a sperm trypsinlike enzyme in the membrane events of the hamster sperm acrosome reaction

Previous studies from this laboratory have suggested a role for sperm trypsinlike activity in the membrane events of the hamster sperm acrosome reaction, but these conclusions have been disputed by studies done with guinea pig, mouse, and ram sperm. This study was designed to further investigate the role of such activity in the hamster sperm acrosome reaction. Washed hamster epididymal sperm were examined by electron microscopy after incubation in a defined medium. Fewer sperm incubated in the presence of the trypsin inhibitor benzamidine underwent the membrane events of the acrosome reaction compared to controls. Benzamidine did not interfere with the loss of the acrosomal contents in the sperm which did undergo acrosome reactions. The trypsin inhibitor NPGB (previously shown to inhibit the hamster acrosome reaction under other conditions) did not inhibit the membrane events or the loss of acrosomal contents when the acrosome reaction was induced by the fusogen lysophosphatidyl choline (a method of induction which may have bypassed the need for a trypsinlike enzyme). In a bioassay designed to measure acrosome reactions, fewer sperm preincubated with benzamidine subsequently penetrated zona-pellucida-free hamster eggs. The present results together with those of an earlier study by this laboratory strongly suggest that a sperm trypsinlike enzyme has a direct or indirect role in the membrane events of hamster sperm acrosome reaction. The relationship of these results to studies with other species is discussed.