OSMOTIC EFFECTS ON VOLUME AND MOTILITY OF BULL SPERM EXPOSED TO MEMBRANE-PERMEABLE AND NONPERMEABLE AGENTS

Factorially arranged experiments were designed to study prefreeze pack ed cell volume (PCV) changes and associated percentages of motile and unstained bull sperm in simple macromolecule-free Tyrode's solution an d egg yolk-Tris (EYT), varying in osmolarity, and with addition of rap idly permeating cryoprotectants, glycerol and 1,2-propanediol, and non permeating substances, sucrose and NaCl. The percentage of motile and unstained sperm was assessed after resuspending sperm in 300 mOsm/L Ty rode's solution. At 25 degrees C PCV increased in Tyrode's solution as osmolarity was decreased from 250 to 150 mOsm/L and decreased as Tyro de's solution was increased to 400 mosmol/L. The relationship of PCV t o the reciprocal of the osmolarity was essentially linear over the ran ge of 150 to 400 mOsm/L, but PCV did not decrease further in solutions ranging from 500 to 1000 mOsm/L. The percentage of motile sperm decli ned to zero in Tyrode's solution at 700 mOsm/L, but 40% of the sperm w ere still unstained in 1000 mOsm/L solutions. The addition of glycerol or 1,2-propanediol had little effect on PCV. With glycerol or 1,2-pro panediol added to 308 mOsm/L Tyrode's solution to give a total of 1267 mOsm/L, there were 49 and 56% motile sperm, respectively, compared to 1% with NaCl added to give 787 mOsm/L. The PCV and percentage of moti le sperm suspended in EYT responded to osmotic changes similar to thos e reported for Tyrode's solution at both 25 and 5 degrees C. Some sper m remained motile after initial exposure to 800 mOsm/L solutions. Thes e findings may have application in improving bull sperm cryopreservati on. (C) 1998 Academic Press.