Passive stretch of adult chicken muscle produces a myopathy remarkably similar to hereditary muscular dystrophy.

The wings of 10 chickens between 1 and 5 years of age were passively extended. An increase in plasma creatine phosphokinase activity was observed in 30 min, continued to rise for 24 h, and then declined, suggesting mechanically induced damage to muscle fibers. Wing muscles were removed and examined histologically at various times after stretch. Patagialis muscles, but not biceps brachii, showed the development of muscle fiber pathology. The patagialis muscle is less active than the biceps brachii and is stretched to a greater degree by wing extension. Susceptibility of muscles to development of pathology appeared to be correlated with the age of the chickens. Pathology was remarkably similar to that observed in young chickens with hereditary muscular dystrophy. Necrotic fibers exhibiting segmental necrosis, abnormal shapes, enlargement, splitting, vacuolation, and phagocytosis were evident. Of particular interest was the appearance of abnormal clusters of acetylcholinesterase activity along the sarcolemma. These sites were shown to appear on fibers of 2-week-old dystrophic chicks prior to necrosis and increase in plasma creatine phosphokinase activity. It is suggested that aging of inactive muscles may promote adhesions between muscle fibers rendering them susceptible to damage when stretched and that necrosis of dystrophic fibers may be initiated by a similar mechanism. Such could occur if the genetic defect resulted in interfiber adhesions. Support for this hypothesis by other reports in the literature is discussed.