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At least 1,549 records · Page 86Linked to original sources
PubMed1991

Effects of glycerol tripalmitate and glycerol trioleate on intestinal absorption of glycerol tristearate.

The goal of the present study was to determine 1) whether the poor digestion and absorption of glycerol tristearate (TS) that we observed previously is due to amount fed and 2) whether the digestion, absorption, and lymphatic transport of TS is affected by the presence of either a saturated fat [glycerol tripalmitate (TP)] or a monounsaturated fat [glycerol trioleate (TO)]. Three groups of intestinal lymph fistula rats were used. Group A was fed a lipid emulsion containing 12.5 mumol of TS (labeled as [glyceryl-1,3-14C]tristerate), 7.8 mumols of egg phosphatidylcholine, and 57 mumols of sodium taurocholate in 3 ml of phosphate-buffered saline per hour for 8 h. Group B rats were fed the same emulsion as group A, but with 12.5 mumols of TO added. Group C rats had 12.5 mumols of TP instead of TO added to the group A emulsion. The lymphatic radioactivity and triglyceride outputs were significantly lower in group A, with group C next and group B having the highest outputs. Significantly more TS remained in the lumen of the group A rats compared with groups B and C. The majority of the radioactivity in the lumen was still in the TS form in all three groups, indicating poor lipolysis. However, once the fatty acid and monoglyceride were absorbed, the reesterification process was similar in all three groups. When we studied the ability of the three groups of animals to transport the absorbed lipid into lymph (lymph transport index), both groups B and C were significantly better than group A rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Intestinal absorption of beta-lactam antibiotics and oligopeptides. Functional and stereospecific reconstitution of the oligopeptide transport system from rabbit small intestine.

The H(+)-dependent uptake system responsible for the enteral absorption of oligopeptides and orally active beta-lactam antibiotics was functionally reconstituted into liposomes. Membrane proteins from rabbit small intestinal brush border membrane vesicles were solubilized with n-octyl glucoside and incorporated into liposomes using a gel filtration method. At protein/lipid ratios of 1:10 and 1:40, the uptake of the orally active alpha-amino-cephalosporin, D-cephalexin into proteoliposomes was stimulated by an inwardly directed H+ gradient and was protein-dependent. In these proteoliposomes the binding protein for oligopeptides and beta-lactam antibiotics of Mr 127,000 could be labeled by direct photoaffinity labeling with [3H]benzylpenicillin revealing an identical binding specificity as in the original brush border membrane vesicles. The uptake system for beta-lactam antibiotics and oligopeptides showed a remarkable stereospecificity; only D-cephalexin was taken up by intact brush border membrane vesicles, whereas the L-enantiomer was not taken up to a significant extent. This stereospecificity for uptake was also seen after reconstitution of solubilized brush border membrane proteins into liposomes demonstrating a functional reconstitution of the peptide transporter. Both enantiomers however, bound to the 127-kDa binding protein as was shown by a decrease in the extent of photoaffinity labeling of the 127-kDa protein in the presence of both enantiomers. After reconstitution of subfractions of brush border membrane proteins obtained by wheat germ lectin affinity chromatography into proteoliposomes, only liposomes containing the 127-kDa binding protein showed a significant uptake of D-cephalexin whereas the L-enantiomer was not transported. The uptake rates for D-cephalexin into proteoliposomes correlated with the content of 127-kDa binding protein in these liposomes as was determined by specific photoaffinity labeling with [3H]benzylpenicillin. The purified 127-kDa binding protein was also reconstituted into liposomes and its ability for specific binding of substrates as well as stereospecific uptake of cephalexin could be restored. These results indicate that the binding protein for oligopeptides and beta-lactam antibiotics of Mr 127,000 mediates the stereospecific and H(+)-dependent transport of orally active beta-lactam antibiotics across the enterocyte brush border membrane. We therefore suggest that this 127-kDa binding protein is the intestinal peptide transport system (or a component thereof).

Affinity Labels↗
PubMed1987

Intestinal absorptive cell tight junctions are linked to cytoskeleton.

Permeation of intercellular tight junctions in epithelia may be altered by maneuvers that affect the cytoskeleton. Conversely, agents that alter tight-junction permeability also often produce alterations in cytoskeletal structure. However, anatomic links between the tight junction and the cytoskeleton have not been clearly defined. We explore the anatomy of the perijunctional cytoskeleton by applying electron microscopy to cytoskeletal preparations of whole intestinal absorptive cells using detergent extraction techniques. Individual elements of the perijunctional cytoskeleton, including actin microfilaments as determined by S1 labeling, appear to associate with the tight junction by means of plaque-like densities that intimately associate with the lateral membrane at the site of the tight junction. Furthermore, such associations are not diffuse within the tight junction, but occur only at sites of fusions ("kisses") between lateral membranes that are thought to represent the specific intrajunctional sites at which the barriers to transjunctional permeation reside. These data provide evidence of intimate cytoskeletal-tight-junction associations, which may represent the anatomical basis for cytoskeletal control of tight-junction permeability.

Absorption↗
PubMed1979

[Postoperative small intestinal absorption after cholecystectomy].

The postoperative resorption in the small intestine after cholecystectomie was found out by means of the modified D-xylose resorption test on the 2-th, 4-th, 6-th an 8-th postoperative day for 14 patients. The velocity and the dimension of the enteral resorption of D-xylose was lower in the immediate postoperative phase. The dimension of the D-xylose resorption was normalized on 4. p. o. day and obtained the preoperative starting-value on the 8-th postoperative day. The myoelectrical activity of the small intestine normalized in a shorter time after cholecystectomy than the enteral resorption. A formal parallelism consists between the normalisation of the motoric activity of the stomach and the xylose-resorption in the immidiate postoperative phase. For the small intestine resorption in the postoperative phase completely clarified and required further investigations. The influences of electrolyte displacement and disturbances of the microcirculation in the postoperative period in the small intestine resorption were discussed.

Adult↗
PubMed2002

Intestinal absorption enhancement of the ester prodrug tenofovir disoproxil fumarate through modulation of the biochemical barrier by defined ester mixtures.

The effect of discrete esters and ester mixtures on the intestinal stability and absorption of tenofovir disoproxil fumarate (tenofovir DF, an esterase-sensitive prodrug of the antiviral tenofovir) was compared with the effect of strawberry extract, which has been shown to enhance the absorption of the prodrug across Caco-2 monolayers and in rat ileum. In addition, the mechanism of absorption enhancement was investigated. In rat intestinal homogenates, complete inhibition of the conversion of tenofovir DF (as obtained by strawberry extract) could only be obtained at relatively high concentrations of the discrete esters or by using mixtures of esters (e.g., propyl p-hydroxybenzoate 0.02%, octyl acetate 0.02%, ethyl caprylate 0.01%). Coincubation of tenofovir DF with this mixture also resulted in an enhancement of its absorption in the in vitro Caco-2 system as well as in rat ileum. As tenofovir DF is a substrate for P-glycoprotein (P-gp)-related efflux carriers in the Caco-2 model, the modulatory effect of the ester mixtures was studied on the functionality of P-gp using cyclosporin A (CsA) as a model substrate. Strawberry extract as well as the mixture of three esters interfered with the absorptive transport of CsA across Caco-2 monolayers, illustrating that both mixtures interfere with both esterase-activity and P-gp functionality. This concerted barrier was not observed in rat ileum, suggesting differential functional activities of the biochemical barrier toward tenofovir DF in different absorption systems. Overall, our results illustrate that modulation of the biochemical barrier (metabolism and efflux) of tenofovir DF by ester mixtures can be used to increase the intestinal absorption of tenofovir DF in an in vitro and an in situ absorption model; the mechanism of action appears to be a complex interplay of different systems; the differential expression of carriers and enzymes in different systems illustrates the difficulty of extrapolating observations between different systems/species.

Adenine↗