Development of the oocyte-penetrating capacity of spermatozoa in the human epididymis.

The development of the penetrating capacity of human epididymal spermatozoa has been assessed in vitro using zona-free hamster oocytes. Spermatozoa were recovered from epididymal tissue of men undergoing vasectomy or epididymovasostomy. The results suggest that human spermatozoa first develop the potential to penetrate oocytes in the proximal corpus region. Spermatozoa recovered from more proximal sites of the excurrent duct failed to bind or fuse with zona-free hamster eggs although a small proportion (3%) in the caput region were capable of progressive motility. The data are discussed in relation to biochemical changes to human spermatozoa during maturation.