Effect of Feeding Different Protein Sources on Plasma and Gut Amino Acids in the Growing Rat

Abstract

Experiments were conducted with growing rats to study the influence of feeding various protein and nitrogen-free diets on plasma amino acid levels and on the bulk amino acid composition of intestinal contents of rats. Feeding of a nitrogenfree, but calorically adequate diet to rats lowered total plasma essential amino acid levels below those noted for rats fed either 9% protein diets or fasted for 18 hours. Diets, whose protein source was solely rumen protozoal protein, when fed to rats resulted in significantly lower (P < 0.01) plasma histidine and valine levels than those noted in rats fed other protein diets or nitrogen-free diets. By 2 hours after feeding, endogenous nitrogen secretions into the gut had extensively diluted the exogenous nitrogen intakes; however, total intestinal amino acid levels were higher in the protein-fed rats than in those fed the nitrogen-free diet. The bulk amino acid compositions of either jejunal or ileal contents 2 hours after feeding were similar regardless of protein source or diet fed.