Osmotic effects on feline spermatozoa from normospermic versus teratospermic donors

Effects of osmolality stresses on the sperm of normospermic (>60% normal sperm/ejaculate) versus teratospermic (<40% normal sperm) domestic cats and the normospermic leopard cat and the teratospermic clouded leopard were studied. Spermatozoa were exposed to various anisotonic solutions in a single step or returned to near isotonic conditions in a single step after exposure to anisotonic solutions. The percentage of sperm motility was measured subjectively, and dual fluorescent stains were used to assess membrane integrity by flow cytometry. The percentage of sperm motility declined (P < 0.05) in domestic cat sperm exposed to osmolalities <200 and >450 mOsm. Spermatozoa from all felines underwent marked (P < 0.05) membrane disruption following a hypotonic stress, but sperm from teratospermic donors experienced greater (P < 0.05) membrane disruption in response to decreased osmolality. While feline spermatozoa appeared to be highly resistant to hypertonic (600, 1200, and 2400 mOsm) conditions, with >85% of the cells maintaining intact membranes, severe membrane disruption occurred when cells were returned to isotonicity in a single step. There was no difference (P > 0.05) between a 1- and 5-min exposure to various anisotonic solutions. Similarly, sperm from normospermic and teratospermic domestic cats responded identically after exposure to ionic or nonionic solute. Results demonstrate that: (1) spermatozoa from teratospermic males are more vulnerable to a hypotonic stress than sperm from normospermic counterparts; (2) in response to small deviations in osmolality, feline sperm experience a more rapid decline in motility than membrane integrity; and (3) an abrupt return to isotonicity after a hypertonic stress causes extensive sperm membrane damage regardless of ejaculate quality.