Effect of corticosterone and protein malnutrition on muscle protein breakdown in vivo in rats as measured by the urinary excretion of 3-methylhistidine

Abstract

The role of corticosterone in regulating the rate of muscle protein breakdown was evaluated by measuring the urinary excretion of 3-methylhistidine (3-Mehis) during the administration of 0.0 (vehicle), 0.8 (physiological dose) and 10 (pharmacological dose) mg of the glucocorticoid/100 g body weight/day to adrenalectomized rats (AdX, AdX 0.8 and AdX 10 respectively).A fourth group of intact rats receiving only vehicle (In) was included as control.Rats were fed on either adequate protein and energy (Co) or low-protein (1-P) diets, for eight consecutive days.No differences were found between AdX and AdX 0.8 groups as compared to the In group in regard to body and liver weights.The AdX 10 group exhibited a significant reduction in body weight and a considerable increase in liver weight; these results were found in rats fed on the Co and 1-P diets, although rats on the 1-P diet showed a proportional decrease in those parameters as compared to the rats fed on the Co diet.Gastrocnemius, tibialis and E.D.L.muscle weights were significantly reduced in AdX 10 group, approximatley at the same extent in the two dietary groups.Soleus muscle weight increased in the AdX 10 group, at the same extent in the two dietary groups, as compared to the In group.Plasma corticosterone levels were significantly greater in the AdX 10 group in both dietary treatments, though restriction of protein in the diet induced a higher plasma hormone level than that of the Co group.Urea-N and creatinine outputs were significantly higher in the AdX 10 group.3-Mehis excretion underwent an immediate and significant rise in the AdX 10 group, although rats fed on 1-P diet showed a more persistent rise than those fed on the Co diet.No differences were found among the other groups.It is concluded that high plasma corticosterone levels can accelerate muscle protein breakdown and that this action is not seriously affected by the protein content of the diet.