title: Effect of experimental hyperthyroidism on skeletal-muscle proteolysis.
abstract: It is not clear whether the muscle wasting commonly observed in hyperthyroidism is due to alteration in the rate of protein synthesis or degradation. The effect of experimental hyperthyroidism on skeletal-muscle proteolysis in the rat was studied by measuring alanine and tyrosine release from isolated skeletal muscles in vitro and 3-methyl-histidine excretion in vivo. Alanine release from the isolated epitrochlaris-muscle preparation was increased as soon as 24h after a 25 microgram dose of L-tri-iodothyronine in vivo. Conversely, alanine release from muscles of hypothyroid rats was decreased, but restored by L-tri-iodothyronine supplementation before death. Furthermore, 3-methylhistidine excretion was increased in hyperthyroid rats throughout an 18-day treatment period. The increased amino acid release from isolated muscles and the increased 3-methylhistidine excretion in vivo strongly suggests that hyperthyroidism increases skeletal-muscle proteolysis. Furthermore, the thyroid-hormone concentration may be an important factor in regulating muscle proteolysis.
mesh_terms: D000409:Alanine / Q000378:metabolism; D000818:Animals; D006980:Hyperthyroidism / Q000378:metabolism* / Q000652:urine; D008297:Male; D008762:Methylhistidines / Q000652:urine; D009124:Muscle Proteins / Q000378:metabolism*; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D013237:Stereoisomerism; D014284:Triiodothyronine / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism
chemical_list: D008762:Methylhistidines; D009124:Muscle Proteins; D014284:Triiodothyronine; D014443:Tyrosine; D000409:Alanine