ZONA-PELLUCIDA AS PHYSIOLOGICAL TRIGGER FOR THE INDUCTION OF ACROSOMEREACTION

To evaluate the kinetics of acrosome reaction, sperm samples from four fertile donors were prepared by swim-up and incubated with solutions of human zonae containing 0.1, 0.15, 0.3, 0.5 and 1.0 zonae mu l(-1) A fter 20, 40 and 60 min of incubation at 37 degrees C, aliquots were ta ken for evaluation of the acrosomal status. The results showed a disti nct time- and dose dependence of the acrosome reaction induced by solu bilized zona proteins. After 60 min of incubation in 1.0 zonae mu l(-1 ), about 80% of the spermatozoa showed signs of acrosomal loss; about 40% were completely acrosome-reacted. In addition, zona-bound sperm sh owed the same ratios of acrosome-reacted spermatozoa in control experi ments. The velocity of acrosome reaction was calculated by means of a double-reciprocal plot being 2.0-2.5% min(-1) for completely reacted s permatozoa and those showing signs of acrosome reaction. However, both subgroups differed considerably in their constants of equilibrium (K= 2.0 ZP mu l(-1) and K=0.2 ZP mu l(-1), respectively). In nonreacted an d partly reacted spermatozoa results might indicate a disturbed course of acrosome reaction or possibly the existence of different subpopula tions in respect of sperm competition.