Abstract
The plantaris muscle in both legs of each experimental animal was overloaded through tenotomy of its synergistic gastrocnemius muscle. The characteristic response pattern of overload involved increase in wet muscular weight, hypertrophy, increase in Average Cross-sectional Area (AFCA) of the muscle fibers and a trend of shift from glycolytic and intermediate fibers towards oxidative fibers. All these basic responses are initially augmented in hyperthyroid situation. Under prolonged (5-10 days) exposure to T4 the overloaded muscles showed degenerative changes such as decline in muscular weight, atrophy and decrease in AFCA while the fiber shifting process continues without any major modification. Fibrosis was another important effect of prolonged exposure to thyroxin. Treatment with thiourea decreased the release of T4. Responses of muscular overload in hypothyroid situation include gradual increase in muscular weight, an increase in AFCA up to 10 days stage, and a progressive shift from glycolytic and oxidative fibers to intimidate fibers. A decrease in AFCA (an indicative of secondary
atrophy in individual muscle fibers) with a concomitant increase in fibrosis was noted at 15 days stage in this experimental group. Conclusively, it is suggested that thyroxin enhances the anabolic and oxidative potentials of skeletal muscles under the stress of overload, but prolonged stress under hyperthyroid conditions lead to degenerative
changes; on the other hand, hypothyroid situations lead to progressive muscular loss in the same stress condition.
KHAJAWA RAEES AHMAD , SAIMA SALEEM, KAUSAR RAEES, ASMATULLAH, SHAHZAD A. MUFTI. (2005) HISTOLOGY, HISTOCHEMISTRY AND MORPHOMETERY OF OVERLOADED SKELETAL MUSCLES UNDER NORMAL, HYPO AND HYPER-THYROID STATUS N PIGEON, Punjab University Journal of Zoology, Volume 20, Issue 2.
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