Activities of enzymes related to the malate-aspartate shuttle in the bloodcells of thoroughbred horses undergoing training exercise

The activities of the enzymes related to the malate-aspartate shuttle, whic h convert cytosolic NADH into mitochondrial NADH, were measured in red and white blood cells from thoroughbred horses undergoing continuous training ( race horses) and compared with those in blood cells from riding horses. The activities of malate dehydrogenase (MDH), a rate-limiting enzyme for the m alate-aspartate shuttle, were significantly elevated in the white blood cel ls (WBC) from race horses compared with those from riding horses. There wer e no significant differences in the activities of the enzymes in the red bl ood cells between race horses and riding horses. This increase in the MDH a ctivity in their WBC is considered to reflect the increased metabolic activ ity in the race horses resulting from the training.