Activities of enzymes in the malate-aspartate shuttle and the isoenzyme pattern of lactate dehydrogenase in plasma and peripheral leukocytes of lactating Holstein cows and riding horses.

The activities of the enzymes involved in the malate-aspartate shuttle and lactate dehydrogenase (LDH) and the pattern of the isoenzymes of LDH were determined in plasma and peripheral leukocytes of lactating Holstein cows and thoroughbred riding horses as representative herbivorous animals. In the horse plasma, LDH activities were significantly lower and AST activities were significantly higher than those in the cow plasma. The specific activities of cytosolic malate dehydrogenase (MDH), LDH and AST in the horse leukocytes were higher than those in the cows. The cytosolic ratio of MDH/LDH activity (ML ratio) in the horse leukocytes was significantly lower than that in the cow leukocytes owing to significantly higher activities of LDH. The ML ratio was considered to reflect the difference in energy metabolism in leukocytes between cows and horses. The plasma LDH isoenzyme patterns of cow and horse showed the characteristic as herbivorous animals with dominance of LDH-1, -2 and -3. The LDH isoenzyme patterns with dominance of LDH-3 and -4 in the horse leukocytes were remarkably different from those in the cow leukocytes. There were significant differences in activities of malate-aspartate shuttle enzymes, ML ratio and LDH isoenzyme patterns in the cytosolic fractions of leukocytes between the lactating cows and the riding horses.