Effect of dietary protein content on tissue protein synthesis rates in Zucker lean rats

Protein synthesis rates were determined in representative tissues of lean Zucker rats fed diets containing varying amounts of protein for 30 days. The control group (RD) received a standard commercial diet (20% of protein-derived energy), the high protein group (HP) received a high protein diet (36% of protein-derived energy) and the hypoproteic group (LP) received a low protein diet (9.5% of protein-derived energy). The contribution of skin and skeletal muscle to the whole body weight is higher in Zucker lean rats than in other rat strains. In all dietary groups the tissues with the highest fractional protein synthesis rates were the small intestine, kidney and liver, followed by lungs, skin and finally muscle. The HP group showed significantly lower protein synthesis in the muscle and skin than the RD group; the LP group showed lower rates in skin, small intestine, kidneys and lungs. The data presented indicate that the adaptations to a diet rich in protein did not affect the rate of protein synthesis, and also that the limited availability of protein reduced the rate of protein synthesis in some visceral organs but not in the skeletal muscle nor the skin. This implies that nitrogen partitioning is adapted to protein availability in the diet. (C) 1999 Elsevier Science Inc.