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

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Abstract
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. Digestion of a high-protein diet apparently results in a series of homeostatic responses: initially plasma amino acid concentrations rise and food intake falls; despite this, protein intake is elevated and activities of enzymes of amino acid concentrations decrease and food intake returns to normal.