EXERCISE-INDUCED NECROTIC MUSCLE DAMAGE AND ENZYME-RELEASE IN THE 4 DAYS FOLLOWING PROLONGED SUBMAXIMAL RUNNING IN RATS

Male Wistar rats were made to run uphill on a treadmill 5.5 degrees incline at 17 m min(-1) for 4 h, and killed for muscle and serum sampling 2, 4, 12, 24, 48, or 96 h after the exertion. To estimate the degree of muscle damage, beta-glucuronidase activity, total protein concentration, water content and morphology were examined in the red parts of quadriceps femoris (MQF) and soleus (MS) muscles, the distal white part of the rectus femoris muscle (MRF) and the superficial part of triceps brachii muscle (MTB). Simultaneous serum samples were assayed for creatine kinase (CK) activity and carbonic anhydrase III (CA III) concentration. Fibre swelling and interstitial oedema were detected in MS at 4 h and in MQF at 12 h and typical histopathological changes, including inflammation and fibre necrosis, in both muscles 12-96 h post-exertion. beta-Glucuronidase activity, a quantitative marker of muscle damage, was increased in MS at 4 h, in MQF at 24 h and in MRF 48 h after the running. No increase occurred in MTB. Water and protein content increased or decreased respectively, faster in MS (2 h post-exercise) than in MQF (12 h) or MRF (12 h). Water content thus contributed to muscle damage by preceding the increase in beta-glucuronidase activity. Serum CK activity was increased 2, 4, and 48 h after the running. Changes in serum CA III concentration were rather similar to those in CK but were not significant. The increase in serum CK was not in concert with the necrotic events in the muscle but occurred considerably earlier (2 h vs. 12-24 h post-exercise). The second peak in CK, 48 h post-exercise (during the necrotic phase), was smaller than the first one. Our results show that serum CK activity is an inaccurate estimate of exercise-induced muscle damage as regards interpretation of the degree and the time course of pathological events in the muscle.