Protein starvation and the small intestine

Abstract

A B ST RA CT Weanling rats were fed diets which contained either no protein or 27% protein. In one experiment after 23-35 days both groups were given l-leucine-4,5-3H either intragastrically or intraperitoneally and then sacrificed 24 hr later. In a second experiment animals were given these diets for 21 days and sacrificed 3, 6, or 12 hr after either intragastric or intraperitoneal administration of the labeled leucine. In both experiments the intestinal mucosa of proximal and distal segments of the small intestine was scraped, weighed, the protein concentration measured, and the specific activty of the mucosal protein was determined.The wet weight of the mucosa and the protein concentration of the mucosa were significantly greater in the control animals than in the protein-depleted animals. The mucosal protein per 100 g of body weight was the same in the protein-deprived and the control groups. The specific activity of the intestinal mucosal protein was higer in the protein-deprived animals than in the control animals.In the protein-deprived animals the proximal segment incorporated more radioactive amino acid into mucosal protein than did the distal segment at 3, 6, 12, and 24 hr after the amino acid was given by mouth. A similar difference was found between the proximal and distal segments of the control animals 6 hr after oral adminisstration of l-leucine-'H. On the other hand, when the l-leucine-3H was given intraperitoneally to both groups

Protein synthesis and growth in the gastrointestinal tract of the young preruminant lamb

“…This contrasted with findings obtained in gastrointestinal tissues of lambs, either by using the constant-infusion technique (Davis et al 1981 ;Schaefer & Krishnamurti, 1984) or by a pulse injection of ~-[U-'~C]lysine (Arnal et al 1983), and demonstrated the advantages of a massive injection of amino acid. However, there is also evidence that lumen amino acids are preferentially utilized for protein synthesis in the small intestinal mucosa (Hirschfield & Kern, 1969;Alpers, 1972). To our knowledge, it has not been verified in large-dose experiments that the specific radioactivity of the label in the lumen amino acid pool approached the specific radioactivity of the precursor in the mucosal tissue homogenate.…”

Regulation of gastrointestinal mucosal growth

“…Nevertheless, epithelial cells of the small intestine are capable of incorporating orally administered amino acids into protein [63,64], and it has been suggested that luminally derived amino acids might be important in the nutrition of the small intestinal mucosa during protein deprivation [63]. If one compares the protein distribution of orally administered amino acids with parenterally administered ones, the patterns are quite different [64].…”

Regulation of intestinal mucosal growth by amino acids

“…These types of results have lead to the suggestion that luminally derived amino acids might be important for nutrition and growth of small intestinal mucosa (Hirschfield and Kern, 1969). However, if one compares the protein distributions of orally administered amino acids with those administered parenterally, the patterns are different (Alpers 1972).…”