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Journal ArticleDOI

The digestion and absorption of protein in man. 1. The site of absorption.

01 Mar 1970-British Journal of Nutrition (Cambridge University Press)-Vol. 24, Iss: 1, pp 227-240
TL;DR: In this article, the absorption of the amino acid components of two protein-containing test meals has been studied in six healthy volunteers, and the results showed that at least 70-75% of the milk protein test meal had been absorbed when the sampling holes were 230 cm from the nose.
Abstract: 1. The absorption of the amino acid components of two protein-containing test meals has been studied in six healthy volunteers. One meal contained 15 g of milk protein and the other contained 15 g of gelatin. In a control experiment a meal was given which contained a negligible amount of protein. 2. The subjects were intubated with a single lumen tube; then each meal was swallowed and intestinal residues were obtained from known levels. The amino acid composition of the intestinal contents was compared with that of the original meal. Correction was made for net water shifts by reference to a non-absorbable marker compound (polyethylene glycol 4000). 3. The results showed that at least 70–75% of the milk protein test meal had been absorbed when the sampling holes were 230 cm from the nose. It is suggested, however, that most, if not all, of the meal had been absorbed when the sampling holes were 140 cm from the nose. 4. Amino acids were absorbed at rates proportional to their concentrations in the meal. 5. Gelatin, a protein known to be relatively resistant to enzymic hydrolysis, was poorly absorbed from the region of the small intestine under study. 6. Estimates of the amount of endogenous protein secreted in response to the test meals ranged from z to 8 g, equivalent to 13–53% of the protein containing test meals. 7. The absorption of certain amino acids, e.g. the dicarboxylic amino acids, was more rapid than was expected; glutamic and aspartic acids are absorbed slowly from a mixture of amino acids, both in vitro and in vivo.

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Citations
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TL;DR: The gram-negative bacterial species Salmonella enterica and Escherichia coli are members of the family Enterobacteriaceae that spend a good part of their lives as residents of animal hosts.
Abstract: The gram-negative bacterial species Salmonella enterica and Escherichia coli are members of the family Enterobacteriaceae that spend a good part of their lives as residents of animal hosts. S. enterica is the etiologic agent of gastroenteritis and typhoid fever in humans ([88][1]), whereas E. coli

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TL;DR: The nature and magnitude of the penetration and enzymatic barriers to peptide and protein drug absorption are described and the effectiveness and limitations of the approaches that have been used to overcome such barriers are reviewed.

388 citations

Journal ArticleDOI
TL;DR: After the ingestion of a test meal containing a substantial amount of protein which is within the usual range of dietary intake, there are greater amounts of amino acids present as small peptides than in the free form in the gut lumen and the ingested protein can be recovered as late as 4 h both in the jejunum and in the ileum.
Abstract: Normal human volunteers were intubated with either aspiration tubes or a biopsy capsule placed in the small intestine. The subjects were then fed a test meal containing 50 g of purified bovine serum albumin which served as the model dietary protein. Electrophoretic analysis of intestinal fluids showed that for at least 4 h the fed albumin was detectable in jejunal and ileal fluids. On separate occasions, subjects were fed the same meal without the protein. No protein was detected in intestinal fluids when the protein-free meal was fed. After the protein-rich meal, total concentrations of measured free and peptide amino acids rose from 3.21 to 29.29, and 15.94 to 117.97 mumol/ml, respectively, (P values < 0.02) in the jejunum. Similarly, total concentrations of measured free and peptide amino acids rose from 5.45 to 19.74, and 13.59 to 65.39, respectively, (P values < 0.05) in the ileum. In contrast, concentrations of free and peptide amino acids in intestinal fluids did not increase after the protein-free meal. While intracellular concentrations of amino acids in the jejunal mucosa did not show significant changes, plasma concentrations of each individual free amino acid were increased after the protein-rich meal and were either decreased or unaltered after the protein-free meal. The amino acid composition of the fed protein was reflected in the increases in intraluminal and plasma concentrations of individual amino acids after the protein-rich meal. It is concluded that after the ingestion of a test meal containing a substantial amount of protein which is within the usual range of dietary intake; (a) the exogenous protein is the principal source of the increased free and peptide amino acids in the intraluminal contents and in the plasma; (b) there are greater amounts of amino acids present as small peptides than in the free form in the gut lumen; (c) the ingested protein can be recovered as late as 4 h both in the jejunum and in the ileum.

363 citations

Journal ArticleDOI
TL;DR: McKnight et al. as discussed by the authors showed that acidified nitrite is bactericidal for a variety of gastrointestinal pathogens such as Yersinia and Salmonella, and that it contributes to the formation of systemic S-nitrosothiols.
Abstract: Based on the premise that dietary nitrate is detrimental to human health, increasingly stringent regulations are being instituted to lower nitrate levels in food and water. Not only does this pose a financial challenge to water boards and a threat to vegetable production in Northern Europe, but also may be eliminating an important non-immune mechanism for host defence. Until recently nitrate was perceived as a purely harmful dietary component which causes infantile methaemoglobinaemia, carcinogenesis and possibly even teratogenesis. Epidemiological studies have failed to substantiate this. It has been shown that dietary nitrate undergoes enterosalivary circulation. It is recirculated in the blood, concentrated by the salivary glands, secreted in the saliva and reduced to nitrite by facultative Gram-positive anaerobes (Staphylococcus sciuri and S. intermedius) on the tongue. Salivary nitrite is swallowed into the acidic stomach where it is reduced to large quantities of NO and other oxides of N and, conceivably, also contributes to the formation of systemic S-nitrosothiols. NO and solutions of acidified nitrite, mimicking gastric conditions, have been shown to have antimicrobial activity against a wide range of organisms. In particular, acidified nitrite is bactericidal for a variety of gastrointestinal pathogens such as Yersinia and Salmonella. NO is known to have vasodilator properties and to modulate platelet function, as are S-nitrosothiols. Thus, nitrate in the diet, which determines reactive nitrogen oxide species production in the stomach (McKnight et al. 1997), is emerging as an effective host defence against gastrointestinal pathogens, as a modulator of platelet activity and possibly even of gastrointestinal motility and microcirculation. Therefore dietary nitrate may have an important therapeutic role to play, not least in the immunocompromised and in refugees who are at particular risk of contracting gastroenteritides.

301 citations

Journal ArticleDOI
01 Feb 1985
TL;DR: It now appears certain that two major mechanisms are involved in the absorption of the luminal products of protein digestion: transport of liberated free amino acids by group specific active amino acid transport systems, and uptake of unhydrolysed peptides by mechanisms independent of the specific amino acid entry mechanisms.
Abstract: Although it has become clear that brush-border hydrolysis, and consequent utilization of the monosaccharide transport system, is the predominant method of absorption of the luminal products of carbohydrate digestion in man, it now appears certain that two major mechanisms are involved in the absorption of the luminal products of protein digestion: ( I ) transport of liberated free amino acids by group specific active amino acid transport systems, and (2) uptake of unhydrolysed peptides by mechanisms independent of the specific amino acid entry mechanisms.

200 citations

References
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Journal ArticleDOI
TL;DR: A modified ninhydrin reagent for the photometric determination of amino acids and related compounds and its application in drug discovery is described.

2,851 citations

Journal ArticleDOI
TL;DR: The method is discussed and compared with earlier methods for the estimation of the glycerides in blood serum and the basic principle is the determination of the Glycerol part of theglycerides after separation of the phospholipids on silicic acid.

271 citations

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How much protein can be absorbed in one sitting?

At least 70-75% of a 15g milk protein meal was absorbed when the sampling holes were 230 cm from the nose.