Biomedical subjects

D M Matthews

Publications and source records attributed to D M Matthews.

At least 91 records · Page 5Linked to original sources

PubMed1975

Changes in plasma amino acid concentrations in man after ingestion of an amino acid mixture simulating casein, and a tryptic hydrolysate of casein.

1. Plasma amino acid levels have been estimated at 0, 15, 30 and 45 min after ingestion of doses of (1) an amino acid mixture simulating casein and (2) a tryptic hydrolysate of casein consisting mainly of oligopeptides. Both doses contained the same amount of nitrogen. 2. After ingestion of both preparations, there was a prompt increase in plasma amino acid levels, followed by a decrease. No such change occurred in fasting subjects. There were no significant differences between increments in plasma amino acid levels after ingestion of the amino acid mixture and the corresponding increments after ingestion of the tryptic hydrolysate. 3. Correlations were found between the areas under the curves for individual amino acid concentrations, after ingestion of the two preparations, and the amino acid composition of casein. The results do not suggest that increases in plasma amino acid levels following small doses of protein digestion products are the result of circadian changes, or that such increases are 'swamped' by absorption of amino acids from endogenous protein in the lumen of the small intestine.

Adult↗

PubMed1975

Evidence for active transport of tripeptides by hamster jejunum in vitro.

1. This paper describes the uptake by rings of everted hamster jejunum in vitro of three peptides with structural features making them resistant to hydrolysis, glycylsarcosylsarcosine, glycylsarcosylsarcosylsarcosine and beta-alanylglycylglycine. 2. Glycylsarcosylsarcosine was taken up by a saturable mechanism and accumulated intact in the intracellular compartment of the intestinal wall, apparently against an electrochemical gradient. Its uptake was reduced by Na+-replacement, anoxia and metabolic inhibitors. It was concluded that uptake of this peptide was the result of Na+-dependent active transport. 3. Glycylsarcosylsarcosylsarcosine was very poorly taken up and its uptake did not appear to be the result of active transport. 4. Beta-Alanylglycylglycine appeared intact in the intracellular compartment of the intestinal wall on a substantial scale though it was not concentrated. No satisfactory evidence of uptake by a saturable mechanism was obtained. Uptake was, however, inhibited by anoxia, 2,4-dinitrophenol and Na+-replacement. Reasons are given for supposing that uptake of this peptide may be the result of Na+-dependent active transport by the same carrier as that utilized by glycylsarcosylsarcosine. 5. The results suggest that provided that they escape brush-border hydrolysis, tripeptides, like dipeptides, are actively transported into the absorptive cells of the intestinal mucosa, but that the ability of these cells to take up peptides by an active mechanism is unlikely to extend to tetrapeptides.

Alanine↗

PubMed1975

A common mechanism for transport of di- and tri-peptides by hamster jejunum in vitro.

1. This paper describes the results of a survey of the effects of peptides and amino acids on uptake by rings of everted hamster jejunum in vitro of glycylsarcosylsarcosine, a tripeptide which is taken up by an active mechanism but is very resistant to hydrolysis, appearing intact in the rings. The results of a small number of similar experiments with beta-alanylglycylglycine, another tripeptide which is taken up with very little hydrolysis, are also described. 2. Uptake of the two tripeptides was inhibited by other di- and tri-peptides, but not by free amino acids. The results suggest that dipeptides and tripeptides share a common uptake mechanism. The tetrapeptide glycylsarcosylsarcosylsarcosine did not inhibit uptake of glycylsarcosylsarcosine, and appears to be unable to utilize the uptake mechanism. 3. The results add to information about the influence of molecular structure on intestinal uptake of peptides by the system used by glycylsarcosylsarcosine, which is shared by a wide range of other di- and tri-peptides. In conjunction with previous results, they suggest that substitution of the N-terminal amino or C-terminal carboxyl groups reduces affinity for transport, that the presence of a beta-amino acid residue in a peptide is tolerated by the transport system, and that the presence of a D-amino acid residue reduces affinity for transport. Some peptides containing or made up of basic or acidic amino acid residues appear to have a low affinity for the transport system used by glycylsarcosylsarcosine. 4. Of two biologically active peptides, one, cephalexin, a peptide antibiotic, inhibited uptake of glycylsarcosylsarcosine and is probably transported by the same system. The other, prolylleucylglycineamide, which has the action of a hypothalamic regulatory factor, did not, and its structural features may make it unsuitable for carrier-mediated transport by the small intestine.

Animals↗

PubMed1975

Jejunal absorption of an amino acid mixture simulating casein and an enzymic hydrolysate of casein prepared for oral administration to normal adults.

1. An intestinal perfusion technique was used in six normal human subjects to study absorption of sixteen individual amino acids from an amino acid mixture simulating casein and from an enzymic hydrolysate of casein, prepared for oral administration to these subjects, which consisted of a mixture of oligopeptides and free amino acids. 2. Total absorption of alpha-amino nitrogen was greater from the casein hydrolysate than from the amino acid mixture, and the considerable variation in percentage absorption of individual amino acids from the amino acid mixture was much reduced when the enzymic hydrolysate solution was perfused, as a number of amino acids which were poorly absorbed from the amino acid mixture were absorbed to a greater extent from the casein hydrolysate. 3. These findings indicate that after extensive intestinal resections or in malabsorption there might be significant nutritional advantages in the administration of protein hydrolysates rather than amino acid mixtures.

Administration, Oral↗

PubMed1975