Effects of cryopreservation on human sperm acrosomes.

Total acrosin activity and acrosomal status were determined before and after cryopreserving human spermatozoa. Three different cryopreservation protocols were used. Both acrosin activity and the incidence of intact acrosomes decreased during cryopreservation. The magnitudes of the decreases were weakly but significantly correlated (r = 0.29, P less than 0.05), suggesting that acrosomal loss contributed to the decrease in acrosin activity. The effects of the three cryopreservation protocols were not significantly different. Motility decreased more (average 43%) than did the percentage of spermatozoa with intact acrosomes (27%) and the total acrosin activity (24%). These measurements suggested that acrosomal damage may have been secondary to cell death. This hypothesis was tested by determining the acrosomal status of spermatozoa that survived cryopreservation. Spermatozoa that were motile after thawing averaged 96% acrosome-intact; their acrosin activity, however, was significantly less than that of motile, unfrozen spermatozoa. These observations support the idea that the acrosomal loss due to cryopreservation is associated with cell death but also demonstrate decreased total acrosin activity of the acrosome-intact spermatozoa that survive cryopreservation.