Muscle contraction and relaxation are slowed in hypothyroidism. Intramuscular metabolism is altered because of modification of Ca 2+-ATPase activity and fluctuations of cytoplasmic Ca2+. The activities of several enzymes involved in muscle glycogen synthesis and catabolism are variable. Some muscular enzymes (transaminases, creatine phosphokinase, lactic dehydrogenase, and their isoforms) are secreted in large amounts in the bloodstream, confusing an ECG diagnosis of myocardial infarction (Bürgiand König 1988).
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