Protein Synthesis Rate in Liver and Muscle of Rats Following Four Days of Overfeeding

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Abstract
Protein synthesis rate in liver and in muscle were determined in control and in 4-day overfed rats. Both the control and the overfed rats received their entire food (liquid diet) by a continuous intragastric infusion through permanently implanted cannulas. Each of the control rats received a daily quantity of the liquid diet which matched its own mean voluntary (ad libitum) intake as determined prior to the experiment. Each of the overfed rats received a daily excess of 35% over its mean daily voluntary intake. Protein synthesis rate was determined using a continuous intravenous infusion of 14C tyrosine. Overfeeding resulted in a 24% reduction (P < 0.02) in the fractional rate of protein synthesis in the liver, and in a 16% reduction in the muscle. Overfeeding also resulted in a reduction in the ratio of RNA/protein amounting to 11% in the liver (P < 0.05) and 21% in the muscle (P < 0.02). These significant reductions in RNA/protein indicate a relative loss of ribosomes and suggest a reduced capacity for protein synthesis. Our data thus demonstrate that overnutrition can be associated with a reduced rate of protein synthesis.