Effect of hyperthyroidism on fibre-type composition, fibre area, glycogen content and enzyme activity in human skeletal muscle.
Seven hyperthyroid patients were studied by repeated muscle biopsies (vastus lateralis) before and after a period of medical treatment which averaged 10 months. The biopsies were analysed with regard to fibre-type composition, fibre area, capillary density, glycogen content and enzyme activities representing the glycolytic capacity (hexokinase, 6-phosphofructokinase), oxidative capacity (oxoglutarate dehydrogenase, citrate synthase) and Ca2+- and Mg2+-stimulated ATPase in muscle. In the pretreatment biopsy (hyperthyroid state), there was a significantly lower proportion of type I fibres (30% vs. 41%), a higher capillary density (23%), lower glycogen content (33%), and higher hexokinase activity (32%) compared with the post-treatment biopsy. No significant changes in the activity of the remaining enzymes were observed. The present study indicates that hyperthyroidism induces a transformation from type I to type II fibres in human skeletal muscle. The increase in hexokinase activity probably reflects a higher glucose utilization by skeletal muscle in order to compensate partially for the reduced glycogen content.
D000328:Adult; D001706:Biopsy; D017301:Ca(2+) Mg(2+)-ATPase / Q000032:analysis; D000252:Calcium-Transporting ATPases / Q000032:analysis; D002950:Citrate (si)-Synthase / Q000032:analysis; D005260:Female; D006003:Glycogen / Q000032:analysis; D006593:Hexokinase / Q000032:analysis; D006801:Humans; D006980:Hyperthyroidism / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism; D008297:Male; D008713:Methimazole / Q000627:therapeutic use; D008875:Middle Aged; D009132:Muscles / Q000032:analysis / Q000473:pathology*; D010732:Phosphofructokinase-1 / Q000032:analysis; D013889:Thiouracil / Q000627:therapeutic use
D008713:Methimazole; D013889:Thiouracil; D006003:Glycogen; D007655:Ketoglutarate Dehydrogenase Complex; D002950:Citrate (si)-Synthase; D006593:Hexokinase; D010732:Phosphofructokinase-1; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases