Amino acid and peptide absorption from partial digests of proteins in isolated rat small intestine.

Abstract

SUMMARY1. Absorption of each of sixteen amino acids, free and peptide-bound, has been measured in isolated rat small intestine perfused with five partial digests of proteins.2. At low concentrations net absorption of each amino acid was proportional to its luminal concentration and independent of the nature of the amino acid.3. A series of first-order multiple regressions was found to describe well the characteristics of absorption.4. Rate constants for disappearance of free and peptide-bound amino acids from the lumen were closely similar. However, substantial back-flux occurred of amino acids derived from peptide hydrolysis. Hence 60-70 % of the amino-N entering the serosal tissue fluid probably had left the lumen as free amino acids.5. Intact peptides crossed the mucosa during absorption from a soy bean hydrolysate and in substantial quantities during absorption from one casein digest but not from another. With other hydrolysates there was no evidence for passage of peptides to the serosa.6. In several cases there was a serious discrepancy between the amount of amino-N absorbed from the lumen and the amount accounted for as peptide or free amino acid in the serosal secretion.7. The characteristics of absorption were similar (apart from the exceptions in 5 above) for all the digests studied except for soy bean hydrolysate.

ABSORPTION OF INTACT PEPTIDES: STUDIES ON TRANSPORT OF PROTEIN DIGESTS AND DIPEPTIDES ACROSS RAT SMALL INTESTINE IN VITRO

“…The results extend the earlier studies of Gardner (1975Gardner ( , 1978a and now confirm that significant, although small, amounts ofpeptides can escape hydrolysis and cross the rat small intestine in intact form. Intact peptides crossed the intestine during perfusion with both the soy-bean and casein digests but not with the Evans Peptone.…”

Effect of Peptide Chain Length on Absorption and Intact Transport of Hydrolyzed Soybean Peptide in Rat Intestinal Everted Sac.

“…The methods for investigation of peptide absorption were essentially those previously used by Gardner [9][10][11]. The amino acid compositions of the serosal fluid and the intestinal mucosa analyzed before the hydrolysis indicated the uptake of peptides as free amino acids.…”

“…The amino acid compositions of the serosal fluid and the intestinal mucosa analyzed before the hydrolysis indicated the uptake of peptides as free amino acids. Peptide-N was estimated as bound-N by the difference method, i.e., from the the increase in free amino acid on acid hydrolysis [10][11][12]. Intact transport was calculated as follows:…”

STUDIES ON THE ABSORPTION OF THE PANCREATIC FUNCTION TEST PEPTIDE, N‐BENZOYL‐L‐TYROSYL‐p‐AMINOBENZOIC ACID, AND RELATED COMPOUNDS BY ISOLATED RAT SMALL INTESTINE

“…Since methods were essentially similar to those used in earlier studies on peptide absorption (Gardner, 1975(Gardner, , 1978a only brief details and differences are given below.…”

“…Peters, Donlon & Fottrell, 1972;Kim, Birtwhistle & Kim, 1972), it is possible that intestinal enzymes might hydrolyse Bz-tyr-PABA; also, at least some intact peptides and possibly proteins can cross the intestine (e.g. Matthews, Addison & Burston, 1974;Matthews, 1975;Gardner, 1975Gardner, , 1978aGardner, , 1979Prockop & Sjoerdsma, 1961;Williams & Hemmings, 1978). Thus, the validity of this diagnostic test depends partly upon Bz-tyr-PABA not being hydrolysed at a significant rate by extra-pancreatic enzymes in the alimentary tract, as well as its not being transported across the intestine in intact form.…”