Evaluation of Six Partially Purified Proteins by Rat Growth, Nitrogen Retention by Young Rats and Liver Regeneration

Abstract

Six partially purified proteins previously compared by the criteria of dog growth and dog maintenance were examined for growth efficiency in rats, nitrogen retention by young rats and liver protein regeneration in rats. The growth in grams per gram of nitrogen eaten was found to be: egg albumin 16.3, whole egg 15.0, beef muscle 13.4, casein 12.8, peanut flour 8.8, gluten 2.4. Similar values were found in a second growth experiment. The apparent digestibilities were much alike, 89 to 94%, and the proportion of absorbed nitrogen retained was in the same order as the growth values. With the exception of the gluten, a linear relationship was found between the gains in weight per gram of nitrogen eaten and the nitrogen retained per gram eaten by the young rats. This is taken to indicate constancy of composition of the body weight gains. Adult rats were found to digest the egg albumin almost competely even when fed at a 40% level. This is in contrast with only 54% digestibility by adult dogs, caused by the presence of an active antitrypsin. Liver protein regeneration was most efficient with casein and gluten, slightly lower with whole egg and significantly retarded with egg yolk or with whole egg to which cholesterol was added in the amounts provided by the raw egg yolk. This decrease in liver regeneration in the presence of cholesterol was not accompanied by an increase in liver solids and therefore probably not by an increase in fat deposition. The importance of recognizing species differences in the utilization of food proteins is indicated by these differences between the dog and the rat with respect to the absorption of egg albumin.