• horse;
  • ions;
  • plasma;
  • erythrocytes;
  • exercise


Six conditioned Arabian horses were subjected to an intermittent exercise test to examine alterations in plasma and erythrocyte ions during exercise. Haematocrit, erythrocyte haemoglobin concentration, plasma potassium [K+] and lactate [La] concentrations increased and plasma sodium [Na+] and chloride [Cl] concentrations decreased during exercise. Erythrocyte [K+] and [La] increased and erythrocyte [Na+] decreased during exercise. When cell volume was held constant at resting values, potassium content of the cells was slightly greater than resting values; and sodium and chloride content decreased during exercise. Increased haematocrit in horses during exercise due to splenic contraction increases the erythrocyte membrane surface area and distribution space for blood ions. Movement of lactate into erythrocytes may modulate the increase in plasma [La), maintaining the muscle to plasma gradient and facilitating the movement of lactate from muscle into plasma.