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Biomedical subjects

D B Silk

Publications and source records attributed to D B Silk.

At least 163 records · Page 9Linked to original sources
PubMed1975

A study of relations between the absorption of amino acids, dipeptides, water and electrolytes in the normal human jejunum.

1. A double-lumen perfusion technique was used to study the effect of a wide range of concentrations of the dipeptide glycyl-L-alanine and its constituent amino acids on water and electrolyte absorption from iso-osmotic solutions in the upper jejunum of normal human subjects. 2. There was no significant absorption of water and electrolytes from sodium chloride solution (150 mmol/l) but the presence of the dipeptide or its constituent amino acids stimulated water and electrolyte absorption. 3. Water absorption reached a peak at increasing amino acid and dipeptide concentrations and then tailed off. Our data suggest that the tailing off is not solely due to the diminished sodium content of the solutions. 4. During perfusion of the dipeptide-sodium chloride and amino acid-sodium chloride solutions solute and water were absorbed as an iso-osmotic solution. Analysis of the results indicates that this could occur at high dipeptide concentrations only if the majority of the dipeptide enters the cell intact.

Adult↗
PubMed1975

A study of intraluminal peptide hydrolase activity in the rat.

1. Uncentrifuged and centrifuged rat intestinal contents were assayed for peptide hydrolase activity with glycyl-L-phenylalanine (Gly-Phe) and L-phenylalanyl-glycine (Phe-Gly) as substrates in the absence and presence of the intestinal cytosol peptide hydrolase inhibitor p-hydroxymercuribenzoate. 2. Jejunal contents hydrolysed Gly-Phe faster than Phe-Gly. Conversely, ileal contents hydrolysed Phe-Gly faster than Gly-Phe. 3. p-Hydroxymercuribenzoate markedly inhibited jejunal peptide hydrolase activity. There was ten times as much PHMB-resistant activity towards both dipeptides in ileal contents as in jejunal contents. 4. Most of the luminal enzyme activity was present in the supernatants after centrifugation, indicating the luminal enzymes exist in the soluble form. Although the presence of soluble bacterial enzymes cannot be excluded, peptide hydrolase enzymes in jejunal contents have the characteristics of mucosal cytosol enzymes whereas enzymes in ileal contents have the characteristics of mucosal bruch border as well as cytosol enzymes.

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

Absorption of two proline containing peptides by rat small intestine in vivo.

1. Glycyl-L-proline and L-prolyl-glycine are two dipeptides that are poorly hydrolysed by brush border peptide hydrolases in vitro. The present study was undertaken to investigate in vivo intestinal absorption of the two dipeptides in male Wistar rats. A steady-state perfusion technique has been used and jejunal and ileal absorption studied by comparing rates of absorption of constituent amino acids from dipeptide and equivalent equimolar amino acid solutions. 2. Glycine and proline were absorbed at the same or faster rates during perfusion of 10 mM glycyl-L-proline than during perfusion of 10 mM-L-prolyl-glycine than during perfusion of its equivalent equimolar amino acid solution. Conversely, the two constituent amino acids were absorbed at slower rates during perfusion of its equivalent amino acid solution. As expected very low concentrations of free amino acids were detected during the jejunal dipeptide perfusions but higher concentrations were detected during the ileal perfusions. 3. The addition of 40 mM L-prolyl-glycine to the 10 mM glycyl-L-proline solution did not affect the rates of disappearance of glycyl-L-proline. The addition of 40 mM glycyl-L-proline to 10 mM L-prolyl-glycine however had a significant inhibitory effect on the disappearance of L-prolyl-glycine. It is concluded that the two dipeptides may be absorbed by different peptide transport systems.

Animals↗
PubMed1975

Ileal function in patients with untreated adult coeliac disease.

A double-lumen perfusion technique has been used to investigate jejunal and ileal absorption of glucose, water, and electrolytes in a group of patients with untreated adult coeliac disease. Correct positioning of the tube was confirmed by measuring the differential jejunal and ileal handling of bicarbonate. Eight control subjects and eight patients with coeliac disease were perfused with an isotonic electrolyte solution containing 50 mM glucose and 25 mM bicarbonate. The group of coeliac patients had impaired jejunal absorption of glucose (P less than 0.001), water (P less than 0.01), sodium (P less than 0.02), and chloride (P greater than 0.05) compared with the control group. In contrast the group of coeliac patients had normal ileal glucose and water absorption and increased ileal sodium (P greater than 0.01) and chloride (P greater than 0.05) absorption compared with the controls. Evidence for ileal adaptation was found in three individual patients who had absorptive values outside 2SD of the normal mean. The results indicate that the distal small intestine in coeliac disease has the ability to adopt to the damage and loss of absorptive capacity in the proximal small intestine.

Adolescent↗
PubMed1975

Jejunal and ileal absorption of dibasic amino acids and an arginine-containing dipeptide in cystinuria.

Ileal transport of dibasic amino acids has not previously been studied in the intestine of healthy volunteers or cystinuric patients. Experiments have therefore been designed to compare ileal and jejunal absorption of lysine and arginine both in normal subjects and cystinuric patients. In addition, jejunal perfusion experiments have been carried out to investigate absorption of the dipeptide L-arginyl-L-leucine. The results indicate that, at the concentrations studied (4.2 mM lysine, 1 mM arginine), severe transport defects exist throughout the whole small intestine for both amino acids in cystinuria. Despite the transport defect for free arginine, cystinuric patients absorbed the dipeptide L-arginyl-L-leucine normally. Because of the transport defect for free arginine, it has been possible to show that during absorption of L-arginyl-L-leucine in cystinuria approximately 30% of dipeptide-bound arginine can be recovered from the gut lumen in the free form. These findings indicate that the prime function of specific amino acid transport systems during the absorption of protein digestion products may be as a "recapture mechanism" for amino acids liberated as a result of mucosal cell peptide hydrolysis.

Adult↗
PubMed1974

Amino acid and peptide absorption in patients with coeliac disease and dermatitis herpetiformis.

A double-lumen perfusion technique has been used to study amino acid and peptide absorption in eight normal control subjects, 13 patients with untreated adult coeliac disease, and 16 patients with dermatitis herpetiformis who had varying morphological abnormalities of the small bowel. All subjects were perfused with isotonic solutions containing 10 mM glycyl-L-alanine and 10 mM glycine + 10 mM L-alanine. Patients with adult coeliac disease had impaired absorption of glycine (p < 0.01) and L-alanine (p < 0.05) from the amino acid solution compared with the control subjects. Amino acid uptake from the dipeptide solution was not significantly impaired, although four individual patients had impaired uptake of both amino acids. In contrast to these findings, very few patients with dermatitis herpetiformis had impaired amino acid absorption from either solution. Sodium absorption was impaired from both solutions when the groups of patients with adult coeliac disease and dermatitis herpetiformis with subtotal villous atrophy and partial villous atrophy were studied, and there were patients in each group who secreted sodium and water. The results suggest that malabsorption of dietary protein is unlikely to occur in dermatitis herpetiformis but may occur and contribute to protein deficiency seen in some severe cases of adult coeliac disease. The impairment of sodium and water absorption provides evidence that there may be functional impairment of the jejunal mucosa in dermatitis herpetiformis as well as in adult coeliac disease.

Adult↗
PubMed1974

Functional differentiation of human jejunum and ileum: a comparison of the handling of glucose, peptides, and amino acids.

The characteristics of glucose, glycine, L-alanine, and glycyl-L-alanine absorption from the jejunum and ileum have been compared in normal human subjects. A perfusion technique has been used, and correct positioning of the perfusion tube has been confirmed by measuring the differential jejunal and ileal handling of bicarbonate. Glucose and glycine were absorbed faster from the jejunum than from the ileum of all subjects studied, and L-alanine was absorbed faster from the jejunum than from the ileum in five out of six subjects studied. In contrast, the dipeptide glycyl-L-alanine was absorbed at comparable rates from the jejunum and ileum. Higher concentrations of free amino acids were detected in the luminal contents aspirated during the ileal dipeptide perfusions.These results emphasize the importance of oligopeptide transport in the absorption of protein digestion products, especially in the human ileum, and the practical implications of these findings are discussed.

Adult↗