EXERCISE-INDUCED CHANGES IN THE ACTIVITIES OF P-GLUCURONIDASE AND N-ACETYL-BETA-D-GLUCOSAMINIDASE IN PLASMA AND MUSCLE OF STANDARD-BRED TROTTERS

The activities of lysosomal enzymes, such as beta-glucuronidase and N- acetyl-beta-D-glucosaminidase, have been shown to increase in muscle a fter endurance exercise. We examined whether measurable activities of lysosomal enzymes are present in equine plasma and whether the exercis e-induced changes in the muscle are reflected in plasma. Six trained S tandardbred trotters performed three exercise bouts with 1 h intervals and the same procedure was repeated 3 days later. Venous blood sample s and muscle biopsies from the middle gluteal muscle were taken before and after exercise. The activities of beta-glucuronidase and N-acetyl -beta-D-glucosaminidase were measured both from plasma and muscle spec imens. Cell infiltration into the muscle after exercise was evaluated by the DNA content and histochemically by haematoxylin stain. The acti vity of N-acetyl-beta-D-glucosaminidase in plasma was increased immedi ately after exercise, but had returned to the basal level at 4 h. N-ac etyl-beta-D-glucosaminidase in muscle and beta-glucuronidase in muscle and plasma increased 2 days after exercise and returned to the basal level on day 3. A similar pattern was seen when the exercise protocol was repeated 3 days later, except that the activities continued to inc rease during the 3 days after exercise. The DNA content in muscle corr elated with beta-glucuronidase in muscle and plasma and with the N-ace tyl-beta-D-glucosaminidase in muscle indicating that the activities re flect the infiltration of phagocytes into the exercise-injured muscle. It can be concluded that the activities of the lysosomal enzymes in p lasma increase after exercise and that the changes are mainly due to a simultaneous increase in the number of neutrophils. Therefore, plasma activities of the lysosomal enzymes are poor indicators of exercise-i nduced muscle damage.