Associations among food and protein intake, serine dehydratase, and plasma amino acids.

ANDERSON, H. L., N. J. BENEVENGA, AND A. E. HARPER. Associations among food and protein intake, serine dehydratase, and plasma amino acids. Am. J. Physiol. 214(5): 1008-1013. 1968.Relationships among liver serine-threonine dehydratase activity, plasma amino acid concentrations, and food and protein intake were studied in growing rats undergoing adaptation to high-protein diets. Serine-threonine dehydratase activity was low initially but increased as protein intake rose above the amount required for rapid growth. Plasma amino acid concentrations were greatly elevated 1 day after animals were fed high-protein diets but, with the exceptions of leucine, isoleucine, and valine, decreased thereafter as serine-threonine dehydratase activity increased. Food intake of rats fed high-protein diets was depressed initially when serine-threonine dehydratase activity was low and plasma amino acid concentrations were high. Food intake rose subsequently as enzyme activity increased and plasma amino acid concentrations decreased. Ingestion of a high-protein diet apparently results in a series of homeostatic responses. l initially plasma amino acid concentrations rise and food intake falls; despite this, protein intake is elevated and activities of enzymes of amino acid catabolism increase; subsequently plasma amino acid concentrations decrease and food intake returns to normal.