EFFECTS OF CRYOPRESERVATION ON THE HUMAN SPERM ACROSOME AND ITS RESPONSE TO A23187

The proportion of human spermatozoa from 28 ejaculates to lose their a crosomes during cryopreservation was measured and correlated with the number that became immotile or lost the integrity of their plasma memb rane. The ability of washed spermatozoa to acrosome react in response to A23187 before and after cryopreservation was compared. Motility was assessed by time-lapse photography; intact acrosomes were stained wit h fluorescein conjugated Pisum sativum agglutinin and dead spermatozoa were stained with bisbenzimide (H33258). Twenty-four per cent of sper matozoa lost their acrosomes during freezing and thawing, but the numb er that did so was not correlated with the number that became immotile or non-viable. Frozen spermatozoa exhibited fewer spontaneous acrosom e reactions than did fresh spermatozoa (5 versus 13% after 4 h), but t hey responded to A23187 in a similar way. Although frozen spermatozoa were significantly more likely to die during the incubation, the data do not suggest that degenerative acrosome loss had a major influence o n the results. In the hamster egg test frozen-thawed spermatozoa achie ved more penetrations than did fresh spermatozoa when stimulated with 0 or 1 mumol A23187 l-1 but considerably fewer when stimulated with 4 mumol A23187 l-1. The following conclusions were made. First, cryopres ervation damage to the acrosome, the plasma membrane and the flagellum can occur independently. Second, acrosome function is maintained afte r cryopreservation as long as the organelle remains mechanically intac t. Third, some spermatozoa that lose their acrosomes during cryopreser vation remain viable and can fuse with zona-free hamster eggs.