Absorption of Amino Acids in Malnourished Rats

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Abstract
The absorption of amino acids in young Wistar rats fed protein and protein-energy deficient diets were studied in vivo using a perfusion technique of intestinal segments. The diets had the following composition: A) 18% protein, 69% carbohydrate, and 8% fat (CTL); B) 4% protein, 14% cellulose and no changes in other constituents (LPR); C) 4% protein, 56.5% carbohydrate and 26.5% cellulose (LPC). The LPR and LPC rats failed to gain weight and became hypoproteinemic after feeding the diets for 4 weeks. At the end of this period, the intestinal transport of tyrosine was higher in the LPR and LPC rats as compared with the CTL animals. The lumen-to-blood flow of tyrosine-3H (UL) was also increased in LPR and LPC rats. However, the uptake of this amino acid by the soluble and protein-bound extracts of the intestinal mucosa was not altered and there was no relationship between the absorption of tyrosine and the free amino acid levels of the intestinal mucosa. The intestinal absorption of this amino acid was inversely correlated with the circulating blood levels. The intestinal transport of leucine was also elevated in malnourished animals. However, the whole blood levels of this amino acid were unchanged. The intestinal transport rates of phenylalanine and glycine were not altered, although glycinemia was elevated in both LPR and LPC rats. The absorption of lysine was lower in the LPR group while blood levels were not modified. The results of this study suggest that in malnourished rats, the intestinal transport of certain neutral amino acids such as tyrosine may be inversely correlated with its concentration in the circulation. However, there was no such correlation for glycine, leucine and lysine.