Effects of Splenic Erythrocytes and Blood Lactate Levels on Osmotic Fragility of Circulating Red Cells in Thoroughbred Horses during Exercise

Abstract

Changes in the packed cell volume (PCV), blood lactate concentration [La^-] and osmotic fragility of circulating erythrocytes were determined in three horses subjected to treadmill exercises or treated with epinephrine. The osmotic fragility was taken as the haemolysis rate (HL) in 0.56% NaCl. Previous warm-up significantly decreased HL by 24%, and cantering at 8 m/s for 8 min (10% incline) increased HL by 92%; subsequent cool-down significantly decreased the rate by 23% to the initial resting level, but thereafter the rate gradually increased again, returning to the initial resting level. In contrast, continuous trotting at 5 m/s for 15 min (0% incline) decreased the HL by 50% to the initial resting level. Intravenous injection of epinephrine had little effect on the HL. Although the exercises in combination with the injection significantly increased PCV and [La^-], these changes in the experiments were not correlated with the HL, but the correlation coefficient for PCV and [La^-] and HL during cantering was positive: r=0.875 and 0.958, P<0.01, respectively. These results suggest that: 1) the release of red cells from the spleen into the circulation has no effect on changes in the osmotic fragility of erythrocytes during exercise; 2) heavy exercise increases the osmotic fragility, but 3) light exercise decreases it.