Ileal Sacs Research Articles

Microvillus-Specific Protein Tyrosine Phosphatase SAP-1 Plays a Role in Regulating the Intestinal Paracellular Transport of Macromolecules

The stomach cancer–associated protein tyrosine phosphatase 1 (SAP-1) is a receptor-type protein tyrosine phosphatase that is specifically expressed on the apical membrane of the intestinal epithelium. SAP-1 is known to maintain the balance of phosphorylation of proteins together with protein kinases; however, its biological function and impact on pharmacokinetics in the intestine remain unclear. The present study, therefore, aimed at clarifying the relationship between SAP-1 and the intestinal absorption behaviors of typical transporter substrates and macromolecules. The endogenous levels of glucose and total cholesterol in the blood were similar between wild-type and SAP-1-deficient mice (Sap1−/−), suggesting no contribution of SAP-1 to biogenic influx. Moreover, in vitro transport study with everted ileal sacs demonstrated that there was no difference in the absorption of breast cancer resistance protein, P-glycoprotein, and peptide transporter substrates between both mice. However, absorptive clearance of macromolecular model dextrans (FD-4 and FD-10) in Sap1−/− mice was significantly higher than that in wild-type mice, and this was confirmed by the trend of increased FD-4 absorption from colonic loops of Sap1−/− mice. Therefore, the results of this study suggest the partial contribution of SAP-1 to the regulated transport of hydrophilic macromolecules through paracellular tight junctions.

Evidence of stereoselective and segmental-dependant transport of chiral antidiabetic drug nateglinide along the rat small intestine: possible role of efflux transporters

The purpose of the study was to investigate whether efflux and stereoselective mechanisms play any role in the transport of nateglinide (NA) enantiomers in rat. The transport of individual enantiomers and racemate was studied with and without the presence of an inhibitor for P-glycoprotein and MRP2, verapamil using duodenal, jejunal, and ileal intestinal sacs prepared from rat intestine. The intestinal samples were analyzed by a validated chiral HPLC method. Generally, higher concentrations of R-NA and its S-enantiomer were observed when the racemate was administered compared to administration of the individual enantiomers. Transport of NA enantiomers when co-incubated with verapamil was increased in the ileum by twofold to threefold with corresponding decreased secretion by almost threefold, while little change in the duodenum and jejunum. The transport of NA from everted sac segments (basal-to-apical side, secretion) was higher than the transport from the normal sac segments (apical-to-basal side, absorption) indicated an involvement of efflux-mediated transport. It has been found that the transport of NA is stereoselective and also regioselective, i.e., R-NA displayed higher efflux than S-NA and it was higher in ileum than the duodenum and jejunum. This study will really pave the way to understand how efflux transporters influence the absorption of chiral compounds when moving across the gastrointestinal tract.

Modulation of the P-Glycoproein-Mediated Intestinal Secretion of Glibenclamide: In Vitro and In Vivo Assessments

The everted gut sac method was used to assess the role of the P-glycoprotein (P-gp) on the intestinal secretion of glibenclamide, a prototype of drug used to treat diabetic mellitus. The study included the evaluation of a P-gp modulator carbamazepine used at equimolar doses in the rat. Furthermore, the influence of carbamazepine on the disposition kinetics of glibenclamide in plasma was characterized. For the in vitro experiments, ileal sacs were incubated with glibenclamide in the presence or absence of carbamazepine. In the in vivo experiments, albino rats of either sex were randomly allocated to two groups (n = 6) and oral treatment with glibenclamide (3.6 mg/kg), alone and coadministration with carbamazepine (90 mg/kg). Blood samples were collected at an interval of 1, 2, 4, 6, and 8 h, respectively. Glibenclamide concentrations in both in vitro and in vivo samples were estimated by a sensitive RP-HPLC method. The rate of glibenclamide accumulation in the intestine wall of everted sacs was significantly lower after its incubation with carbamazepine when compared to glibenclamide alone treated. In the agreement with the in vivo and in vitro experiments, the presence of carbamazepine induced an enhancement in the concentrations of glibenclamide in plasma and gastrointestinal tract. The results obtained in this study, both under in vivo and in vitro conditions confirm the relevance of P-gp-mediated transport to the intestinal secretion of glibenclamide.

Ingestion of potato starch containing high levels of esterified phosphorus reduces calcium and magnesium absorption and their femoral retention in rats

Many studies have shown that esterified phosphorus (P) in diets has a favorable effect on mineral absorption in humans and animals. Phosphorylated oligosaccharides derived from potato starch increase calcium (Ca) absorption from the rat intestine both in situ and in vitro. We hypothesized that the feeding of potato starch has a potential to increase Ca or magnesium (Mg) absorption. Male Sprague-Dawley rats at 7 weeks were fed 4 types of diet containing either 60% sucrose, cornstarch, or 1 of 2 types of potato starch with different P contents for 1, 3, or 5 weeks. A balance test for Ca, Mg, and P was undertaken, and these mineral contents in the femur were determined for the 4 diet groups at each feeding period in vivo. Ingestion of potato starch increased Ca, Mg, and P excretion into feces and decreased the absorption rate of Ca and Mg. Femoral Ca contents were also decreased in the rats fed the potato starch diets compared with those in rats fed the sucrose or cornstarch diet. In vitro experiment in Ca absorption was undertaken using everted jejunal and ileal sacs of the small intestine in male Sprague-Dawley rats (7 weeks old). The potato starch application did not induce significant increase in Ca absorption compared with nonstarch (control) or cornstarch application. In conclusion, the ingestion of potato starch does not increase Ca and Mg absorption and rather accelerates their excretion, inducing the decrease in mineral absorption and retention in growing rats.

<i>In Vitro</i> Studies on the Absorption and Interactions of Zinc, Copper, Manganese and Iron in Rat

Background: The exact details of the processes of trace metals absorption and interactions in the gastro intestinal tract remain uncertain. Absorption for the most part, takes places in the small intestine. The exact site of maximum absorption, as defined either by kinetic rate or quantity has not been clearly defined. Similarly, the luminal and cellular interactions of trace metals are not vividly known. Therefore, the present study was designed to throw more light on these two phenomena. Objective: To examine the absorption and interactions of zinc, copper, manganese and iron in rat intestine. Method: Everted duodenal and ileal gut sacs were prepared from adult male Wistar albino rats in the post absorptive state. The sacs were filled with 0.15M Tris-Krebs buffer, pH 7.3 free from the metals whose absorption and interactions were to be investigated until slightly distended. The uptake of Zn, Cu, Mn and Fe was studied at specific concentration ranges. Sacs were incubated for 30 minutes at 370C with continuous aeration in media containing the same buffer and different concentrations of metals. For the interaction studies, only duodenal sacs were used. All the sacs were incubated as for the absorption studies, Zn, Cu, Mn and Fe were introduced into the different media in pairs or singly for the controls at concentrations of 5.0mM, 9.0mM, 7.0mM and 6.0mM respectively. Results: The absorption of Zn in the duodenum and ileum, Cu in the ileum and Fe in the duodenum were by a saturable carrier mediated process. The absorption of Cu in the duodenum, Fe in the ileum and Mn in both the duodenum and ileum were, most likely, by simple diffusion. As for the interaction experiments, Zn and Cu inhibited uptake of the other, as did Zn and Fe. Cu also depressed Mn uptake under the conditions used but not vice versa. Conclusion: The absorption of trace metals occur equally well in the duodenum and ileum, and the interactions of metals studied may be of nutritional significance under normal conditions as well as in conditions of nutritional imbalance. Keywords : Gut sac, Duodenum, Ileum, interaction, trace metals, absorption. NQJHM Vol. 15 (3) 2005: pp. 110-114

Intestinal secretory and absorptive function in Trichinella spiralis mouse model of postinfective gut dysfunction: role of bile acids

Objective:Observations showing that bile acid malabsorption is frequent in irritable bowel syndrome (IBS) suggest that alterations in bile acid-induced secretion and absorption could contribute to IBS-associated diarrhoea. The secretory response...

Effects of manganese source and calcium on manganese uptake by in vitro everted gut sacs of broilers' intestinal segments

Three experiments were conducted with everted gut sacs to investigate the effects of Mn source and Ca on Mn absorption in different intestinal segments of broilers. In Experiment 1, the Mn uptake by everted sacs of duodenum, jejunum, and ileum after different incubation times was compared to determine an optimum incubation time. In Experiment 2, 8 different Mn sources, including MnSO4, organic Mn sources (Mn-amino acid chelates, Mn-amino acids complexes with different complex strength), and mixtures of MnSO4 with Gly or Met were used to assess the effect of Mn source on Mn uptake. In Experiment 3, the effect of Ca in media on the uptake of Mn from MnSO4 and Mn-amino acids complexes was investigated. The uptake percentages of Mn by everted ileal sacs were significantly higher than those by duodenal and jejunal sacs. The uptake of Mn as Mn-Met chelate was significantly higher than that of Mn as Mn-Gly chelate. The uptake percentages of Mn as Mn-amino acid complex with moderate complex strength (Mn-AA A) and Mn-amino acid complex with strong complex strength (Mn-AA B) were significantly higher than that of Mn as MnSO4. The uptake of Mn as Mn-AA B by jejunal sacs was significantly higher than that of Mn as Mn-AA A in media containing high level of Ca. The uptake percentages of Mn at high Ca level were significantly higher than those at normal level. The results indicate that when incubated in vitro, ileum was the main site of Mn absorption for broilers. The absorption of Mn as organic sources were higher than that of Mn as inorganic Mn. The absorption of Mn as Mn-AA B with strong complex strength by jejunal sacs was higher than that of Mn as Mn-AA A with moderate complex strength in media containing high level of Ca. As a ligand, Met was more effective in facilitating Mn absorption than Gly. Furthermore, the transportation of Mn through intestinal cells was enhanced by adding Ca as CaCl2 to the buffer solutions.

MODULATION OF THE P-GLYCOPROTEIN-MEDIATED INTESTINAL SECRETION OF IVERMECTIN: IN VITRO AND IN VIVO ASSESSMENTS

The everted gut sac method was used to assess the role of the P-glycoprotein (P-gp) on the intestinal secretion of ivermectin (IVM), an antiparasitic widely used in human and veterinary medicine. The work included the evaluation of two different P-gp modulators [itraconazole (ITZ) and valspodar (PSC833)] used at equimolar doses in the rat. Furthermore, the influence of both P-gp modulator agents on the disposition kinetics of IVM in plasma, liver, and gastrointestinal tissues was characterized. For the in vitro experiments, ileal sacs were incubated with IVM (3 microM) in the presence or absence of either ITZ (10 microM) or PSC833 (10 microM). In the in vivo experiments, male Wistar rats were randomly allocated to three groups (n=18) and subcutaneously treated with IVM (200 microg/kg-1), alone and coadministered with ITZ (5 mg, two doses) or PSC833 (8.6 mg, two doses). Animals were sacrificed between 6 and 96 h. Blood, liver, and gastrointestinal samples were collected. IVM concentrations were determined by high performance liquid chromatography. The rate of IVM accumulation in the intestinal wall of everted sacs was significantly higher after its incubation with ITZ (0.115 nmol/g/min) and PSC833 (0.238 nmol/g/min) than that obtained after the incubation without the P-gp modulators (0.016 nmol/g/min). In agreement with the in vitro experiment, the presence of ITZ and PSC833 induced an enhancement in the concentrations of IVM in plasma and gastrointestinal tissues. The results obtained in the current work, both under in vivo and in vitro conditions, confirm the relevance of P-gp-mediated transport to the intestinal secretion of IVM.

Absorption of taurocholic acid by the ileum of normal and transgenic ΔF508 cystic fibrosis mice

Changes in intestinal transport in cystic fibrosis (CF) include both defective Cl(-) secretion and alterations in absorption. This study focused on the effects of CF on the active re-absorption of bile acids in the ileum of normal and transgenic CF mice. Taurocholic acid absorption was monitored as changes in short-circuit current (SCC) in intact and stripped ileal sheets from normal (Swiss) and transgenic CF (Cftr(tm2Cam)) mice with the DeltaF508 mutation. Taurocholic acid uptake was measured directly in everted ileal sacs and in brush-border membrane vesicles (BBMVs) using radiolabelled bile acid. Taurocholic acid caused a biphasic increase in SCC in both intact and stripped ileal sheets from Swiss mice. The initial phase of the response was associated with active bile acid absorption as it was inhibited by a low mucosal Na(+) concentration, but unaffected by Cl(-)-free conditions, serosal furosemide or mucosal diphenylamine-2-carboxylic acid (DPC). The first phase was concentration-dependent and was reduced in the presence of other actively transported bile acids. Intact ileal sheets from wild-type Cftr(tm2Cam) mice also exhibited a biphasic SCC response to taurocholic acid, but in CF tissues the initial phase was reduced and the second phase was absent. Taurocholic acid was actively taken up by everted ileal sacs from Swiss mice. This process was inhibited by a low mucosal Na(+) concentration or the presence of other actively transported bile acids. A similar taurocholic acid uptake was observed in ileal sacs from wild-type mice, but in those from CF mice transport of the bile acid was significantly reduced. However, taurocholic acid uptake was similar in BBMVs from wildtype and CF ilea. Active absorption of taurocholic acid occurs in mouse ileum and this process is reduced in transgenic mouse models of CF with the DeltaF508 mutation. However, this difference cannot be detected in an isolated preparation of brush-border membranes.

Novel phenanthridinone inhibitors of poly (adenosine 5'-diphosphate-ribose) synthetase: potent cytoprotective and antishock agents.

To synthesize novel inhibitors of the nuclear enzyme poly(adenosine 5'-diphosphate [ADP]-ribose) synthetase (PARS), also known as poly(ADP-ribose) polymerase (PARP), and to test them in in vitro models of oxidant-induced cytotoxicity and in endotoxin and splanchnic occlusion-reperfusion-induced shock. Randomized, prospective laboratory study. Research laboratory. Murine macrophages, thymocytes, and endothelial cells; Balb/c mice and Wistar rats. Macrophages and endothelial cells were treated with peroxynitrite and bleomycin to induce PARS activation, and thymocytes were treated with peroxynitrite to induce cell necrosis. Novel PARS inhibitors were synthesized and used to reduce PARS activation and to reverse cytotoxicity. Balb/c mice were subjected to splanchnic occlusion and reperfusion and were pretreated with various doses (1-10 mg/kg intraperitoneally) of PJ34, a selected, potent, water-soluble PARS inhibitor. The passage of fluorescein isothiocyanate-conjugated dextran (4 kDa) was analyzed in everted gut ileal sacs incubated ex vivo as an index of gut permeability. Wistar rats were subjected to Escherichia coli bacterial lipopolysaccharide (40 mg/kg intraperitoneally). PJ34 was also used at 10 mg/kg intraperitoneally, 1 hr before lipopolysaccharide or at 25 mg/kg intraperitoneally 1 hr after lipopolysaccharide treatment. Serum concentrations of indicators or multiple organ injury, concentrations of various proinflammatory mediators, and tissue concentrations of myeloperoxidase and malondialdehyde were measured. In addition, survival rates and vascular contractile and relaxant responses were recorded. Appropriate modifications of the phenanthridinone core structure yielded significant increases in the potency of the compounds, both as PARS inhibitors and as cytoprotective agents. The compound N-(6-oxo-5,6-dihydro-phenanthridin-2-yl) -N,N-dimethylacetamide (designated as PJ34) was one of the potent PARS inhibitors of the series, and it dose-dependently protected against thymocyte necrosis, with a half-maximal restoration of cell viability of 35 nM and complete protection at 200 nM. PARS activation also was visualized by immunohistochemistry and was dose-dependently suppressed by PJ34. The effect of PJ34 was dose-dependently reversed by excess nicotinamide adenine dinucleotide (oxidized). The PARS inhibitors dose-dependently suppressed proinflammatory cytokine and chemokine production and restored viability in immunostimulated macrophages. PJ34 was selected for the subsequent in vivo studies. PJ34 significantly protected against splanchnic reperfusion-induced intestinal hyperpermeability in the mouse. PJ34 reduced peak plasma concentrations of tumor necrosis factor-alpha, interleukin-1beta, and nitrite/nitrate in the plasma of lipopolysaccharide-treated rats. PJ34 ameliorated the lipopolysaccharide-induced increases in indexes of liver and kidney failure and concentrations of myeloperoxidase and malondialdehyde in the lung and gut. Lipopolysaccharide elicited vascular dysfunction, which was normalized by PJ34. Lipopolysaccharide-induced mortality was reduced by PJ34 (both pre- and posttreatment). The novel series of phenanthridinone PARS inhibitors have potent cytoprotective effects in vitro and significant protective effects in shock and reperfusion injury in rodent models in vivo.

Effect of hydroxyzine on the transport of etoposide in rat small intestine.

Etoposide, an anti-neoplastic agent and a substrate of P-glycoprotein (P-gp), exhibits variable oral bioavailability. P-gp, the multidrug resistance gene (mdr1) product, has been considered as an absorption barrier against intestinal drug absorption. Terfenadine, an antihistamine, has been shown to be a P-gp inhibitor. The current study was designed to assess the effect of hydroxyzine, an antihistamine, on the transport of etoposide in the small intestine. Everted rat gut sacs were used to determine the absorption and exsorption of etoposide under different conditions, as rhodamine 123 was chosen to evaluate the role of P-gp in the drug interaction. The results showed that the transport of etoposide was significantly increased from the luminal site to the serosal site in the jejunum by 2- and 4-fold after 90 min in the presence of hydroxyzine and quinidine, respectively. A similar trend was observed in the ileal sacs. This in vitro exsorption study also demonstrated that hydroxyzine could reduce the efflux of etoposide to the luminal site in either jejunum or ileum. The effect of hydroxyzine on the pharmacokinetics of etoposide differed by the in vivo route of administration, thus assuming clinical importance for chemotherapeutic treatment.

Ingestion of the soluble dietary fibre, polydextrose, increases calcium absorption and bone mineralization in normal and total-gastrectomized rats

We previously demonstrated that feeding a highly fermentable and water-soluble dietary fibre, guar-gum hydrolysate (GGH) increased intestinal absorption of insoluble Ca salts in total-gastrectomized rats. In the present study, we examined the effects of feeding a less fermentable and water-soluble fibre, polydextrose (PD), on Ca absorption and bone mineralization in the normal and total-gastrectomized rats in comparison with the effects of GGH. Apparent Ca absorption was severely lowered by gastrectomy, and PD feeding (50 g/kg diet) partially restored the reduction of Ca absorption similarly to GGH feeding (50 g/kg diet). PD feeding also increased the Ca absorption in normal rats, but not GGH feeding. Femur Ca concentration was reduced with gastrectomy. Feeding PD for 21 d increased the bone Ca concentration in both normal and gastrectomized rats, but GGH feeding did not. In rats fed PD, pH of the caecal contents was lower than in rats fed fibre-free and GGH diets; however, soluble Ca concentration in the caecal contents was not different between the diet groups. Short-chain fatty acid concentrations were much lower in the PD groups than in the GGH groups. We also examined in vitro Ca absorption by using everted sacs of the small intestine. Addition of PD to the serosal medium of the ileal sacs increased Ca absorption, but addition of GGH did not. These results suggest that the small intestine rather than the large intestine is responsible for the increase in Ca absorption in rats fed PD, and suggests that the mechanism for the increase by PD may be different from that by GGH.

Poly (ADP-ribose) synthetase mediates intestinal mucosal barrier dysfunction after mesenteric ischemia.

Peroxynitrite-mediated DNA strand breaks trigger poly (ADP-ribose) synthetase (PARS) activation, resulting in intracellular energetic failure and organ dysfunction. We investigated the role of PARS activation on the inflammatory and functional response of the intestine to mesenteric ischemia-reperfusion injury. Anesthetized rats exposed to 15 min occlusion of the superior mesenteric artery showed an increased mucosal PARS activity (ex vivo incorporation of radiolabelled NAD+ in gut mucosal scrapings) as soon as 10 min after reperfusion. During the first 30 min of reperfusion, significant mucosal damage developed, as well as mucosal hyperpermeability to a 4000 MW fluorescent dextran (FD4). These alterations were significantly reduced by treatment with the NO synthase inhibitor L-NMA, which blocks the production of peroxynitrite, as well as with the PARS inhibitors 3-aminobenzamide and nicotinamide, whereas they were markedly enhanced by the glutathione depletor L-buthionine-(S,R)-sulfoximine. Also, PARS inhibition significantly reduced ileal neutrophil infiltration (myeloperoxidase activity) at 3 h reperfusion. In a second set of experiments, the effects of 15 or 30 min ischemia followed by 3 h reperfusion were evaluated in PARS knockout and wild-type mice. Significant protection against histological damage, neutrophil infiltration, and mucosal barrier failure (evaluated by the mucosal-to-serosal FD4 clearance of everted ileal sacs incubated ex vivo) was noted in PARS knockout mice, who also showed reduced alterations in remote organs, as shown by lesser lipid peroxidation (malondialdehyde formation) and neutrophil infiltration in the lung and liver. In conclusion, PARS plays a crucial role in mediating intestinal injury and dysfunction in the early and late phases of mesenteric reperfusion. Pharmacological inhibition of PARS may be a novel approach to protect tissues from reperfusion-related damage.

Mucoadhesive DL-Lactide/Glycolide Copolymer Nanospheres Coated with Chitosan to Improve Oral Delivery of Elcatonin

The purpose of this work was to develop a novel mucoadhesive DL-lactide/glycolide copolymer (PLGA) nanosphere system to improve peptide absorption and prolong the physiological activity following oral administration. The desired PLGA nanospheres with elcatonin were prepared by the emulsion solvent diffusion method to coat the surface of the resultant nanospheres with a mucoadhesive polymer such as chitosan, poly(acrylic acid), and sodium alginate. Their mucoadhesive properties were evaluated by measuring the nanospheres adsorbed to a rat everted intestinal sac (in vitro). The chitosan-coated nanospheres showed higher mucoadhesion to the everted intestinal tract in saline than the other polymer-coated nanospheres. There was no mucoadhesion site-specificity of the chitosan-coated nanospheres between duodenal, jejunal, and ileal sacs. The payload of drug in the chitosan-coated nanospheres was successfully increased by using the solvent diffusion method in oil. The pattern of drug release of the resultant nanospheres did not differ markedly from that of uncoated nanospheres. The chitosan-coated nanospheres with elcatonin were administered intragastrically to fasted Wistar rats. The chitosan-coated nanosphere reduced significantly the blood calcium level compared with elcatonin solution and uncoated nanospheres, and the reduced calcium level was sustained for a period of 48 hr. Even under nonfasting conditions, the mucoadhesion of chitosan-coated nanospheres was unaltered and the reduction in blood Ca levels was maintained satisfactorily.

Effects of DFA IV in rats: calcium absorption and metabolism of DFA IV by intestinal microorganisms.

Di-D-fructose-2,6':6,2'-dianhydride (DFA IV) is a disaccharide consisting of two fructose residues that can be prepared from levan by levan fructotransferase from Arthrobacter nicotinovorans GS-9, and it can be expected to have novel physiological functions from its unique structure. In this study, the effects of DFA IV on calcium absorption and the metabolism of DFA IV by intestinal microorganisms were studied in rats to examine the physiological functions of DFA IV. The apparent calcium absorption in rats fed with DFA IV was significantly higher than that in the control rats, and it seems that calcium absorption had almost been completed at the end of the small intestine. DFA IV also increased the calcium absorption in in vitro experiments, using everted jejunal and ileal sacs, and this result supports the finding obtained in the in vivo experiments. These results indicate that DFA IV may have a function for increasing the calcium absorption in the small intestine of rats. However, the effect in the large intestine could not be clearly observed because of the lack of calcium that reached there. The results of analyses of organic acids in the cecal and colonic contents and of DFA IV in the fecal, cecal, and colonic contents showed that the metabolism of DFA IV by microorganisms in the large intestine progressed gradually, and that DFA IV was converted mainly to acetate, butyrate, and lactate.

Effects of difructose anhydride III on calcium absorption in small and large intestines of rats.

Difructose anhydride III (DFA III; di-D-fructo-furanose 1,2':2,3' dianhydride) was prepared from inulin with Arthrobacter sp. H65-7 inulin fructotransferase (depolymerizing (inulase II; EC 2.4.1.93). DFA III is not hydrolyzed by enzymes in the small intestine, but is metabolized by microorganisms in the large intestine. We investigated the effects of DFA III on calcium absorption in two experiments. In the in vivo experiment, we examined the effects of DFA III, fructooligosaccharides, and raffinose on calcium absorption in male Sprague-Dawley rats 5 weeks old at start of the experiment and given feed containing 3% of one of these oligosaccharides for two weeks. The apparent calcium absorption was significantly higher in rats fed any of these oligosaccharides than in control rats, and the increase with DFA III was the greatest. Absorption in both the small and large intestines was affected. In rats fed DFA III, the cecal wall thickened and soluble calcium and the amounts of some organic acids were higher than in the control groups. In an in vitro experiment with everted jejunal and ileal sacs of rats, calcium absorption was higher when DFA III was present in the mucosal fluid at all concentrations tested (up to 200 mM). In the jejunal sacs, the increase in calcium absorption depended on the DFA III concentration. In the ileal sacs, the absorption was maximum at 50 mM DFA III and did not increase further at higher concentrations. These results indicate that intact DFA III stimulates calcium absorption in the small intestine, and that cecal fermentation of DFA III may contribute to the increase in calcium absorption by the large intestine.

Procyanidin from Black Beans (Phaseolus vulgaris) Inhibits Nutrient and Electrolyte Absorption in Isolated Rat Ileum and Induces Secretion of Chloride Ion

Dietary tannins are reported to impair the absorption of nutrients and minerals in whole animals and in semi-isolated intestinal preparations. The present studies investigated the effect of purified procyanidin from black beans (Phaseolus vulgarus) on tissue electrical parameters, isotopic Na+ and Cl- fluxes and Na+-dependent absorption of labeled glucose by isolated rat ileum. In short-circuited ileal preparations, 0.5–2 g/L procyanidin (PC) inhibited Na+ and Cl- absorption and stimulated Cl- secretion, with consequent increases in short circuit current (Isc), total tissue conductance and transepithelial voltage. The effect was not blocked by indomethacin (20 µmol/L). Also, PC significantly inhibited the glucose-dependent and phlorizin-sensitive component of Isc; a similar result was obtained for the alanine-dependent fraction of Isc. In everted ileal sacs PC inhibited Na+-dependent uptake of labeled glucose, but not passive uptake, by a noncompetitive mechanism. The effects of PC are reminiscent of those of recognized intestinal secretagogues and suggest that the antinutrient effects of condensed tannins involve stimulation of intestinal secretion at the expense of absorption. The results argue against use of black bean broth or cooking liquor in rehydration media for treatment of secretory diarrhea.

Effects of 2164U90 on ileal bile acid absorption and serum cholesterol in rats and mice.

2164U90, [(3R,5R)-trans-3-butyl-3-ethyl-2,3,4,5-tetrahydro-5-phenyl-1,4- benzothiazepine 1,1-dioxide], was found to be a potent inhibitor of the ileal bile acid active transport system. In vitro, 2164U90 decreased uptake and active transport of taurocholic acid by rat everted ileal sacs with IC50s of 4.0 microM and 1.5 microM, respectively. In vivo, 2164U90 produced dose-dependent increases in 23,25-75Se-labeled homocholic acid taurine (SeHCAT) fecal excretion in rats and mice at doses of 3-30 mg/kg and 1-10 mg/kg, respectively. In rats, 30 mg/kg 2164U90 was equivalent to 500 mg/kg cholestyramine. Two days oral administration of 10 mg/kg 2164U90 to rats decreased the bile concentrations of total bile acids 42%, orally administered [3H]taurocholic acid ([3H]TC) 82%, and cholesterol 35%. Cholestyramine (500 mg/kg) had effects similar to 2164U90 on total bile acid and orally administered [3H]TC concentrations but had no effect on biliary cholesterol. The hypocholesterolemic activity of 2164U90 was determined in cholesterol-cholic acid-fed rats and cholesterol-cholic acid-coconut oil-fed mice. 2164U90 inhibited the dietary-induced increase in dextran sulfate-precipitable lipoprotein cholesterol (VLDL+LDL) at doses comparable to doses needed to increase the fecal excretion of bile acids. These data indicate that 2164U90 decreases bile acid absorption by inhibiting the ileal bile acid active transport system, resulting in hypocholesterolemic activity.

Inhibition of ileal sodium-dependent bile acid transport by 2164U90.

Inhibition of the ileal bile acid active transport system, previously shown to be mechanism underlying the hypocholesterolemic activity of 2164U90 in rodents, was further characterized in isolated intestinal preparations from three species. 2164U90 inhibited sodium-dependent transport of taurocholic acid by Caco-2 cells and by monkey and human ileal brush border membrane vesicles in a concentration-dependent manner with IC50s of 7 microM, 5 microM, and 2 microM, respectively. In rat ileal brush border membrane vesicles, 2164U90 was a competitive inhibitor of sodium-dependent taurocholic acid uptake with an estimated Ki of 1.8 +/- 0.2 microM. In anesthetized rats, 5 microM 2164U90 placed in the isolated distal ileum with 3 mM [3H]taurocholic acid decreased ileal uptake, transport into the bile, and transport rate of taurocholic acid by 31-35%. Stereospecificity of inhibition by 2164U90 was demonstrated by the relative inactivity of three other possible stereoisomers in rat ileal sacs and brush border membrane vesicles. 2164U90 did not inhibit sodium-dependent glucose transport by monkey jejunal brush border membrane vesicles, indicating that 2164U90 may be specific for the bile acid transporter. These results suggest that 2164U90 is a potent, selective, stereospecific, competitive inhibitor of the sodium-dependent bile acid transporter in the ileal mucosal cell brush border membrane.

Taurocholate Transport by Everted Ileal Sacs from Rats with differing Protein Nutrition.

Taurocholate Transport by Everted Ileal Sacs from Rats with differing Protein Nutrition.