Effect of trypsin inhibitors on acrosome reaction of guinea pig spermatozoa

Synthetic trypsin inhibitors known to inhibit acrosin were incubated with capacitated guinea pig spermatozoa to determine their possible effects on the membrane vesiculation and acrosomal matrix dispersion steps of the acrosome reaction. As seen by phase-contrast microscopy, the inhibitors nitrophenyl p-guanidinobenzoate, benzamidine and p-aminobenzamidine delayed acrosome reactions induced synchronously in capacitated spermatozoa. Electron microscopy revealed that the membrane vesiculation step of the acrosome reaction was unaffected by treatment of the spermatozoa with trypsin inhibitors, but that dispersion of the acrosomal matrix was blocked in the inhibitor-treated spermatozoa. These results suggest that in the guinea pig, proteinase activity (most likely that of acrosin) is involved in the dispersion of the acrosomal matrix following the membrane vesiculation step of the acrosome reaction, but not in membrane vesiculation.