Capacity of goat epididymal spermatozoa to undergo the acrosome reaction and subsequent fusion with the egg plasma membrane.

The capacity to undergo the acrosome reaction and subsequent fusion with the egg plasma membrane was examined in goat epididymal spermatozoa. Spermatozoa from the proximal and distal caput and distal cauda were preincubated in a sealed glass tube for induction of the acrosome reaction, and their viability, acrosome morphology and penetrability into zona-free hamster eggs were determined. A simplified triple-stain technique revealed that most of the preincubated live spermatozoa in the samples from the distal caput and distal cauda epididymides underwent morphological changes that indicated the occurrence of the acrosome reaction. Electron microscopic examination revealed that the outer acrosomal membrane of many spermatozoa in these samples showed fusion at multiple sites to the plasma membrane. However, the rates of acrosome-reacted cells in the proximal caput spermatozoa were still lower. The sperm penetration assay demonstrated that the penetration rates of distal caput and distal cauda spermatozoa preincubated for 2 h were 93% and 74% respectively, whereas proximal caput spermatozoa scarcely penetrated into eggs. These results indicate that increasing numbers of goat spermatozoa improve in the functions related to the acrosome reaction and subsequent fusion with the egg plasma membrane during their transit through the caput epididymidis.