OSMOTIC EFFECTS ON RAM AND HUMAN SPERM MEMBRANES IN RELATION TO THAWING INJURY

The effects of hyposmotic and hyperosmotic stresses on ram and human s permatozoa were examined. Human spermatozoa exhibited a precipitate de cline in survival at osmolalities below 90 mOsm caused by cells swelli ng beyond their maximum volume-to-surface area ratio and lysing. Ram s permatozoa exhibited a progressive decline in cell survival at relativ ely small hyposmotic stresses before exceeding their maximum volume-to -surface area ratio; this prelytic cell loss could be prevented by dec reasing the osmolality in a series of 25-mOsm steps. Repeated hyposmot ic stress experiments indicated that cells sensitive to prelytic damag e constitute a discrete subpopulation within the ram ejaculate. Sperma tozoa of both species were apparently resistant to hyperosmotic stress es; human spermatozoa maintained membrane integrity when subject to st resses up to 2.5 Osm and ram spermatozoa up to 1 Osm. However, ram spe rmatozoa suffered an almost complete and irreversible loss of motility above 600 mOsm. Spermatozoa of both species exposed to hyperosmotic s tress and returned to isosmotic conditions exhibited significant cell damage, although ram spermatozoa were the more vulnerable. These obser vations are related to cryopreservation of spermatozoa. (C) 1994 Acade mic Press, Inc.