Osmotic sensitivity of canine spermatozoa

The objective of this study was to determine osmotic tolerance of canine spermatozoa. The study comprised three experiments: (1) spermatozoa suspended either in an egg yolk-citrate (EYC) extender or in Kenney skim milk extender were exposed to NaCl solutions ranging from 290 to 1500 mOsm; (2) spermatozoa suspended in EYC were exposed to 550 to 1500 mOsm solutions of glucose, galactose, or fructose; and (3) spermatozoa suspended in EYC or glucose-bovine serum albumin (G-BSA) were exposed to 0.6 M (∼900 mOsm) or 1.2 M (∼1600 mOsm) solutions of glycerol, ethylene glycol (EG), or dimethyl sulfoxide (Me₂SO). In all experiments, motility and membrane integrity of spermatozoa were assessed after they were diluted into isotonic medium at 37 °C. Exposure of canine spermatozoa to solutions of either NaCl or monosaccharides at osmolalities > 500 mOsm caused a significant reduction of motility (P < 0.01). Motility of spermatozoa was more affected by osmotic stress than their membrane integrity. Osmotic sensitivity of canine spermatozoa was dependent on the type of extender; spermatozoa suspended in the Kenney extender were more resistant to osmotic stress than those suspended in the EYC extender. Despite their sensitivity to exposure to high concentrations of nonpermeating agents, canine spermatozoa were rather resistant to exposure to glycerol and EG. However, Me₂SO was toxic to canine spermatozoa; motility was substantially reduced after spermatozoa were exposed to 0.6 M Me₂SO. The type of extender also affected the sensitivity of canine spermatozoa to Me₂SO; spermatozoa suspended in the EYC extender were more resistant than those suspended in G-BSA. It was concluded that canine spermatozoa are sensitive to osmotic stress, but are tolerant to shrinking and swelling caused by exposure to permeating cryoprotectants.