Osmotic Effects on Volume and Motility of Bull Sperm Exposed to Membrane Permeable and Nonpermeable Agents

Factorially arranged experiments were designed to study prefreeze packed cell volume (PCV) changes and associated percentages of motile and unstained bull sperm in simple macromolecule-free Tyrode's solution and egg yolk-Tris (EYT), varying in osmolarity, and with addition of rapidly permeating cryoprotectants, glycerol and 1,2-propanediol, and nonpermeating substances, sucrose and NaCl. The percentage of motile and unstained sperm was assessed after resuspending sperm in 300 mOsm/L Tyrode's solution. At 25 degreesC PCV increased in Tyrode's solution as osmolarity was decreased from 250 to 150 mOsm/L and decreased as Tyrode's solution was increased to 400 mosmol/L. The relationship of PCV to the reciprocal of the osmolarity was essentially linear over the range 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 declined to zero in Tyrode's solution at 700 mOsm/L, but 40% of the sperm were 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-propanediol 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 motile sperm suspended in EYT responded to osmotic changes similar to those reported for Tyrode's solution at both 25 and 5 degreesC. Some sperm remained motile after initial exposure to 800 mOsm/L solutions. These findings may have application in improving bull sperm cryopreservation.