METABOLIC RESPONSE TO STANDARDIZED EXERCISE TEST IN STANDARD-BRED TROTTERS WITH RED-CELL HYPERVOLEMIA

Plasma concentrations of lactate, amino acids, ammonia and products of purine catabolism were studied before, during and after a standardise d incremental exercise test in 29 Standardbred trotters admitted to th e clinic for exercise tolerance testing. According to their fed cell v olume the horses were divided into red cell normovolaemic and fed cell hypervolaemic (polycythaemic) groups. The exercise-response curve for taurine differed significantly in the two groups, whereas all the oth er amino acids behaved similarly. The [branched-chain amino acid]/[ala nine] ratio, a proposed indicator for the use of amino acids in glucon eogenesis, was at rest significantly higher in the polycythaemic horse s. Postexercise concentrations of ammonia and allantoin, both end prod ucts of ATP breakdown, were lower in the polycythaemic horses. No diff erences were observed in the V-LA4 and V-200 markers for lactate and h eart rate responses to incremental exercise, the oxidative capacity of the gluteus medius muscle, the enzyme activities or the post-exercise concentration of lactate, uric acid and hypoxanthine. It is concluded that horses with red cell hypervolaemia behave in a submaximal standa rdised exercise test on a treadmill in the same way as do red cell nor movolaemic horses. The results suggest that the rate of amino acid uti lisation in gluconeogenesis and the ability of amino acids to produce energy aerobically may be elevated in polycythaemic horses.