Distribution and morphology of skeletal muscle lesions after experimental restraint stress in normal and stress-susceptible pigs.

Six normal and 22 stress-susceptible (SS) pigs were subjected to experimental restraint stress to test the hypothesis that SS pigs are more affected by stress-induced skeletal muscle lesions than normal pigs. The stress was provoked by a 12 min intravenous infusion of the myorelaxant succinylcholine at a dose which induced leg paralysis. At necropsy 2-3 days after the stress, 24 muscles were examined macro- and microscopically. The plasma levels of noradrenaline and adrenaline increased significantly during the stress, especially in SS pigs. Significantly higher scores of acute muscle lesions (degeneration and phagocytosis) were recorded in the SS pigs than in the normal pigs. The antebrachial flexor muscles, m. gastrocnemius, crural flexor muscles, m. serratus and m. intercostalis were most affected, while m. semitendinosus, m. masseter, crural extensor muscles, m. quadriceps and antebrachial extensor muscles were the least affected. The muscle regeneration of SS pigs was greater than that of normal pigs indicating more active rhabdomyolysis in SS pigs than in normal pigs. The muscle lesions were also reflected in increased serum levels of creatine kinase (CK), aspartate aminotransferase (ASAT), potassium and creatinine in SS pigs. It is concluded that the restraint stress induced skeletal muscle lesions and increased sympathetic activity, predominantly in SS pigs. It was also shown that certain skeletal muscles are more affected by rhabdomyolysis than others.