Effect of glucagon on concentration of several free amino acids in plasma

Abstract

The protein catabolic influence of glucagon is known to be accompanied by a significant drop in the total plasma free amino acid concentration. In these studies carried out on four subjects it has been shown that the plasma concentration of threonine, proline, glycine, alanine, lysine, arginine, citrulline, serine, cystine and histidine were very significantly lowered by catabolic doses of glucagon ( 3 4 -1 mg. every 6 hours ). The concentration of methionine, valine, and tyrosine were significantly lowered. The leucine level was probably significantly lower than control values. Only the phenylalamine concentration was not significantly affected in these studies. The effect was noted 30 minutes after injection of glucagon in one subject. Urinary amino acid nitrogen declined slightly. The pattern of the glucagon effect on amino acid concentrations was quite similar to that of progesterone which is also catabolic. In the glucagon studies, only the concentrations of glycine and cystine were so lowered that even following a high protein meal when plasma levels rise, they were as low or lower than fasting non-treatment levels. It is suggested that the catabolic effect of glucagon and progesterone is due primarily to an enhancement of hepatic utilization of amino acids, and that the resulting lowered plasma level of one or several amino acids enhances mobilization of more amino acids from peripheral tissues. On the basis of these studies and the plasma amino acid levels observed during catabolic processes induced by progesterone, thyroid and glucocorticoids, it is suggested that the glycine concentration in plasma may be responsible for regulating the mobilization of amino acids. Only the concentration of this amino acid was either lowered or uninfluenced during all four catabolic processes.