In-vitro stimulation on the rat epitrochlearis muscle. II. Effects of catecholamines and nutrients on protein degradation and amino acid metabolism.

The influence of catecholamines and branched-chain amino acids (BCAA) plus insulin on protein degradation and amino acid metabolism was investigated in isolated and electrically stimulated rat epitrochlearis muscles. 10(-7) M adrenaline significantly increased the total amount of muscle tyrosine during 40 min of stimulation with 50 Hz (I s min 1) pulse trains. On the other hand, BCAA + insulin at normal and five times normal plasma concentrations had no effect on muscle tyrosine. Muscle 3- methylhistidine was not influenced by any of the treatments. Muscle release and content of aspartate, alanine, glutamate and glutamine showed individual response characteristics to catecholamines and BCAA + insulin. The data indicate that adrenaline can induce an increased total protein degradation in rat fast muscle during acute contractions in vitro and, furthermore, that BCAA + insulin does not retard protein breakdown during acute muscle contraction.