The effect of stretch removal on muscle weight and proteolytic enzyme activity in normal and dystrophic chicken muscles

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Abstract
Hypertrophy was induced in the patagialis (PAT) muscle of 6-week-old normal and dystrophic chicks by passive stretch for 1 week. Stretch was then removed and muscle weights and activities of the proteolytic enzymes cathepsin C, cathepsin D, and leucine aminopeptidase (LAPase) were measured after 3, 5, 7, 10, and 14 days. In both genotypes, weights of stretch-released muscles dropped progressively for 7 days relative to control muscles, after which they were not significantly different. At the time of stretch release, proteolytic enzyme activities were approximately twice as high in stretched normal muscles as in normal control muscles. In dystrophic chicks there was no difference in activities between stretched and control muscles. However, the activities of the enzymes in dystrophic muscles were already about 4 times higher than in normal control muscles. After stretch release, the enzyme activities in normal muscle progressively fell for 10 days, after which they were not different from normal control muscles. In dystrophic muscles the enzyme activities remained elevated and were not different from dystrophic control muscle activities at any time. We conclude that degradative enzyme activities in normal muscle closely parallel changes in muscle weight, whereas in dystrophic muscle proteolytic enzymes remain elevated and constant whether the muscle is gaining or losing weight.