The Magnitude and Significance of the Protein Reserves in Rats Fed at Various Levels of Nitrogen

Abstract

Rats were fed at various levels of casein or wheat gluten protein in a semi-purified diet from the time of weaning, over a period of 28 days. Gain in body weight and protein-to-DNA and RNA-to-DNA ratios in liver and muscle were determined at the end of the experimental period. Maximal body weight was obtained in rats fed 15% of casein protein, whereas the highest intakes resulted in a slight decrease in growth rate. Liver size, protein-to-DNA and RNA-to-DNA ratios increased with the quantity of casein consumed. The protein-to-DNA ratio in the muscles, however, increased to a maximum in animals fed 15% of casein protein in the diet and decreased when greater amounts of protein were consumed. When animals were pre-fed 9 or 70% of casein, the average survival time during starvation and protein deprivation was significantly less than that for animals fed 18% of casein. The animals pre-fed 40% of wheat gluten survived for a shorter time than the animals fed 9% of casein even though the 2 groups had gained an equal weight over the pre-feeding time. The ability of the animal to resist the stress of food deprivation appeared to be correlated with the magnitude of the protein-to-DNA ratio in the muscles.