CHRONIC LOW-PROTEIN INTAKE REDUCES TISSUE PROTEIN-SYNTHESIS IN A PIG MODEL OF PROTEIN-MALNUTRITION

To determine the effect of severe chronic protein deficiency on protei n synthesis in different tissues and total protein in plasma, and on p lasma biochemical constituents involved in amino acid metabolism, we f ed diets containing either 20 or 3% protein to two groups of four age- matched piglets. After consuming the diets for 8 wk, the pigs received a primed constant infusion of H-2(3)-leucine for 8 h to measure the f ractional synthesis rates (FSR) of tissue protein and total protein in plasma. Plasma urea and amino acid concentrations, particularly indis pensable amino acids, were significantly lower in protein-deficient pi gs. Fractional protein synthesis rates were lower in skin by 66% (P < 0.01), in jejunal mucosa by 50% (P < 0.05), in masseter muscle by 40% (P < 0.05), and in liver by 25% (P < 0.02); the fractional synthesis r ate of the longissimus muscle was not different than controls. Althoug h plasma protein concentration was significantly (P < 0.01) lower in p rotein-deficient pigs, the fractional synthesis rate of the total intr avascular plasma protein pool was not different. We conclude that adap tation to a low protein diet involves a reduction in the rate of prote in synthesis in most body tissues, with the most marked changes occurr ing in skin and intestine, two tissues which frequently exhibit severe functional impairment in protein malnutrition.