1. In the present investigation with rings of everted rat small intestine, carbohydrate gelling agents (plant polysaccharides) such as guaran, pectin, tragacanth, carubin and carrageenan were employed to study their direct effect on intestinal absorption of α-methyl-d-glucoside, d-galactose, l-leucine and l-phenylalanine. 2. Inhibition was found to correlate with the viscosity of the incubation medium, a function only of the polysaccharide concentration, and was independent of other properties of the carbohydrate gelling agents. 3. Reversal of this inhibition was achieved either by washing the tissue free of polysaccharide or by raising tissue agitation. 4. Uptake kinetics in polysaccharide-containing solutions revealed a marked increase of the apparent Michaelis constant although the maximal transport capacity remained essentially unaltered. 5. Since there was no binding of the substrate by the polysaccharides under experimental conditions as judged by a membrane filtration technique, it is concluded that carbohydrate gelling agents may impair intestinal absorption by means of an increased unstirred layer resistance.

1. The kinetics of 2-min uptake of l-lysine and l-lysyl-l-lysine have been studied by using rings of everted hamster intestine in vitro , and values for K t and V max , established. 2. On a molar basis, mediated uptake was more rapid for the amino acid than for the peptide. Non-mediated uptake was more rapid for the peptide than for the amino acid. 3. Comparison of relative rates of uptake of lysine from equivalent solutions of lysine and lysyl-lysine showed that at low concentrations, uptake of lysine was less rapid from the peptide than from the amino acid, whereas at high concentrations, uptake of lysine was more rapid from the peptide than from the amino acid. This type of effect of concentration on relative rates of uptake from equivalent solutions of amino acid and peptide has not previously been described.

1. This paper describes an investigation of the kinetics of influx of the dipeptide glycylsarcosine and the amino acids glycine and l-leucine into rings of everted hamster small intestine in vitro , in proximal and distal small intestine (jejunum and ileum). Results were expressed per unit wet weight of intestine. 2. At all concentrations studied (0·1–100 mmol/l), influx of glycylsarcosine was more rapid in the jejunum than in the ileum. In contrast, at all concentrations studied, influx of glycine and leucine was more rapid in the ileum than the jejunum. 3. Estimates of the simple diffusion component in total influx were made. This component became increasingly large as the substrate concentration was raised. After correction for simple diffusion, transport of all three substrates conformed to Michaelis-Menten kinetics in both jejunum and ileum. Values for simple diffusion, apparent K t and V max. are reported. 4. Possibly physiological implications of the results are discussed, and it is pointed out that under experimental conditions similar to our own, simple diffusion is too large a component in total influx to be ignored.

1. This paper reports the results of experiments on competition for transport by hamster jejunum in vitro between carnosine (β-alanyl-l-histidine) and other peptides and amino acids. Carnosine was chosen because this dipeptide is taken up intact with very little hydrolysis, which simplifies interpretation of the results. 2. Jejunal uptake of carnosine was inhibited by equimolar glycylglycine, glycylglycylglycine, glycylsarcosine, glycylproline, methionylmethionine and prolylhydroxy-proline but not by the equivalent free amino acids, or by a mixture of β-alanine and histidine. Inhibition of carnosine uptake by glycylproline was shown to be competitive. It is suggested that carnosine and the dipeptides inhibiting its uptake enter the mucosal cells by a common mechanism which is independent of the entry mechanisms for amino acids. Uptake of carnosine was not inhibited by N -acetylglycylglycine or by glycylglycine amide, suggesting that these substitutions prevent glycylglycine utilizing the dipeptide-uptake mechanism. 3. Carnosine uptake was not inhibited by equimolar lysyllysine or α-glutamylglutamic acid, nor did lysyllysine and α-glutamylglutamic acid affect uptake of each other. Though these results are compatible with the existence of multiple dipeptide-uptake systems in the intestinal mucosa, the evidence at present available is insufficient to permit any conclusion on this point.

1. A double-lumen perfusion technique has been used in man to study jejunal absorption of individual amino acids from an amino acid mixture simulating casein, and a tryptic hydrolysate of casein consisting of oligopeptides and amino acids. 2. Total absorption was greater from the tryptic hydrolysate than from the amino acid mixture. There was wide variation in the extent to which individual amino acids were absorbed from the amino acid mixture. This was decreased when the tryptic hydrolysate was perfused. Amino acids which were particularly poorly absorbed from the amino acid mixture were absorbed to a substantially greater extent from the tryptic hydrolysate. 3. The results suggest that the characteristics of absorption of amino acid mixtures do not represent those of absorption of the physiological products of intraluminal digestion, oligopeptides and amino acids.