Comparison of phenol red and polyethyleneglycol as nonabsorbable markers for the study of intestinal absorption in humans

Effects of xylitol on carbohydrate digesting enzymes activity, intestinal glucose absorption and muscle glucose uptake: a multi-mode study

Some possible mechanisms behind the anti-diabetic effects of xylitol have been understood from the results of this study.

Acetaminophen inhibits intestinal p-glycoprotein transport activity

Repeated acetaminophen (AP) administration modulates intestinal P-glycoprotein (P-gp) expression. Whether AP can modulate P-gp activity in a short-term fashion is unknown. We investigated the acute effect of AP on rat intestinal P-gp activity in vivo and in vitro. In everted intestinal sacs, AP inhibited serosal-mucosal transport of rhodamine 123 (R123), a prototypical P-gp substrate. R123 efflux plotted against R123 concentration adjusted well to a sigmoidal curve. Vmax decreased 50% in the presence of AP, with no modification in EC50, or slope, ruling out the possibility of inhibition to be competitive. Inhibition by AP was absent at 0°C, consistent with interference of the active transport of R123 by AP. Additionally, AP showed no effect on normal localization of P-gp at the apical membrane of the enterocyte and neither affected paracellular permeability. Consistent with absence of a competitive inhibition, two further strategies strongly suggested that AP is not a P-gp substrate. First, serosal-mucosal transport of AP was not affected by the classical P-gp inhibitors verapamil or Psc 833. Second, AP accumulation was not different between P-gp knock-down and wild-type HepG2 cells. In vivo intestinal absorption of digoxin, another substrate of P-gp, was assessed in the presence or absence of AP (100 μM). Portal digoxin concentration was increased by 214%, in average, by AP, as compared with digoxin alone. In conclusion, AP inhibited P-gp activity, increasing intestinal absorption of digoxin, a prototypical substrate. These results suggest that therapeutic efficacy of P-gp substrates can be altered if coadministered with AP.

A single dose of intravenous esomeprazole decreases gastric secretion in healthy volunteers

BACKGROUND

Data suggest that esomeprazole decreases gastric secretion.

AIMS

To assess the effect of a single i.v. esomeprazole dose on gastric secretion volume 3 h after drug administration, as a primary endpoint, and to evaluate, as secondary endpoints, the reduction 1 and 5 h after dosing; time when the gastric pH was <2.5 and esomeprazole's safety.

METHODS

In all, 23 healthy Helicobacter pylori-negative volunteers (10 men, 13 women, mean age 28.2 +/- 6) participated in this single-centre, randomized, double-blind, placebo-controlled, 2-way, single-dose cross-over study. In different sessions, volunteers received i.v. either esomeprazole 40 mg or placebo. An inserted double-lumen nasogastric tube perfused and aspirated gastric liquid. Mechanical fractioned aspiration measured secretion volume; aliquot spectrophotometry assessed gastric secretion volume lost to the duodenum.

RESULTS

Three hours post-i.v. esomeprazole, average gastric secretion decreased by 77.6% (vs. baseline) compared to placebo. Values 1 and 5 h after dosing were 73.5% and 74.5%. Five hours after esomeprazole, the gastric pH was <2.5 3.9% of the time and 73.3% after placebo (P < 0.002). Esomeprazole was well-tolerated. No serious adverse events occurred.

CONCLUSIONS

Intravenous esomeprazole decreases gastric secretions. The potential clinical impact in averting bronchoaspiration during anaesthesia induction and in intensive care patients should be investigated in further studies.

Sorbitol-based osmotic diarrhea: Possible causes and mechanism of prevention investigated in rats

AIM: To study the possible causes of sorbitol (S)-based diarrhea and its mechanism of reduction by rice gruel (RG) in cecectomized rats.

METHODS: S was dissolved either in distilled water or in RG (50 g/L) and ingested as a single oral dose (1.2 g/kg body mass, containing 0.5 g/L phenol red as a recovery marker) by S (control) and S + RG groups (n = 7), respectively. This dose is over the laxative dose for humans. Animals were sacrificed exactly 1 h after dose ingestion, without any access to drinking water. The whole gastro-intestinal tract was divided into seven segments and sampled to analyze the S and marker remaining in its contents.

RESULTS: Gastric-emptying and intestinal transit were comparatively slower in the S + RG group. Also, the S absorption index in the 3^rd and last quarter of the small intestine (24.85 ± 18.88% vs 0.0 ± 0.0% and 39.09 ± 32.75% vs 0.0 ± 0.0%, respectively, P < 0.05) was significantly higher in the S + RG group than in the control group. The S absorption index and the intestinal fluid volume are inversely related to each other.

CONCLUSION: The intestinal mal-absorption of S is the main reason for S-based osmotic diarrhea. Where RG enhanced the absorption of S through passive diffusion, the degree of diarrhea was reduced in cecectomized rats.

Animal and human models for studying effects of drugs on intestinal fluid transport in vivo

The understanding of the physiology and pathophysiology of intestinal fluid transport has been derived from animal and human models of normal and perturbed intestines. This understanding helped in designing drugs and changing the composition of oral rehydration solutions in a targeted manner to affect intestinal fluid absorption/secretion that was tested both in vitro and in vivo before embarking on clinical trials. In this review, in vivo techniques used to study water transport in both animal and human models are described. In particular, steady state intestinal perfusion techniques, closed segment techniques, fistulous animal models, balance study models, enteropooling models, and isotope tracer models are reviewed. Advantages and drawbacks of each technique and examples where drug effects have been studied in a particular model are provided.

Active transport of 3-O-methyl-glucose by the small intestine in chronically catheterized rats

A method is described for determining the fraction of intestinal 3-O-methyl-glucose (3OMG) absorption that occurs by active transport in chronically catheterized rats without the influence of anesthesia or surgical bowel manipulation. That fraction was determined by simultaneously measuring portal venous-aortic blood concentration gradients (delta C) of 3-O-methyl-glucose (3OMG) and L-glucose, metabolically inert analogues of D-glucose. 3OMG is actively and passively absorbed by the same mechanisms as D-glucose, L-glucose is only passively absorbed. The fraction of 3OMG that is actively transported was calculated from the difference between 3OMG and L-glucose absorption, divided by total 3OMG absorption. We found that more than 94% of 3-O-methyl-glucose is absorbed by active transport when luminal concentrations range from 50 to 400 mM. We conclude that in unrestrained, unanesthetized chronically catheterized rats, most 3OMG is actively absorbed by the intestine even at high luminal concentrations.

Gastrointestinal transit and digestibility of maltitol, sucrose and sorbitol in rats: a multicompartmental model and recovery study

Using data obtained with a dye marker and the gavage technique, the kinetics of gastrointestinal transit of different loads of sugar substitutes (maltitol, sorbitol) and sugar (sucrose) in the rat were analysed using a linear multicompartmental model over a range from the realistic to the non-physiologic high, of carbohydrate intake levels and using only a few experimental time points. The model gave detailed insight into intestinal propulsion and gastrocecal transit time. Rate constants of transport between the compartments investigated were determined; they showed characteristics which could be related to the substance and the dosage administered. Analyses of the gastrointestinal content and calculations of the intestinal net water movement showed that the digestibility and absorption of the disaccharide sugar alcohol, maltitol, in the small gut depended inversely on the dose ingested. For all substances tested, caloric availability in the small intestine was calculated. At a physiological low level of maltitol intake, the results also indicated an insignificant calorie-saving effect in comparison to sucrose, an effect based mainly on the slow absorption rate of the maltitol cleavage product sorbitol.

Experimental models for the investigation of water and solute transport in man. Implications for oral rehydration solutions

For patients suffering from mild to moderate dehydration, oral rehydration therapy has proved a simple and efficacious treatment. There remains, however, a need to develop improved oral rehydration solutions (ORS), and suitable experimental models are required to develop and assess new formulations. The ideal model for such investigations would take into account rates of gastric emptying, influx and efflux of water and solutes in the intestine, and the consequent changes in body composition. As no such definitive model is currently available, a variety of techniques are used to examine parts of the process of intestinal absorption. Clinical studies which assess the recovery of dehydrated patients during therapy using different ORS will ultimately evaluate the efficacy of treatment. However, ethical considerations, the relative insensitivity of this technique and the exacting nature of such studies make this approach unsuitable for the development of specific ORS. Gastric emptying of solutions can be determined by a variety of techniques, among which the radioactive tracer method offers the advantage of having no direct effect on the emptying rate, giving almost continuous measurement and allowing the use of relatively small volumes of fluids. Perfusion techniques allow measurement of the net flux of water and solute in predetermined sections of the intact human intestine. Measurement of the rate of accumulation in the circulation of orally ingested tracer molecules for water and solutes can estimate unidirectional flux. This method allows for the rates of gastric emptying and intestinal absorption of the test substance, but the rate of efflux of the tracer from the vascular space must be known to calculate net uptake. Each of these models has limitations, and care must be taken in interpreting the results in a clinical context. However, their use in the development of improved formulations is well established.

Studies of intestinal permeability in inflammatory diseases using polyethylene glycol 400

It has been proposed that increased bowel permeability might play a role in the pathogenesis of inflammatory disease. Intestinal permeation was investigated by measuring the 6-hour urinary excretion of polyethylene glycol (PEG) 400 in 40 adult volunteer controls and in patients with inflammatory disease. Of the patients, 15 had Crohn's disease; 7, ulcerative colitis; 2, celiac disease; and 7, rheumatoid arthritis. No significant difference in total urinary excretion over a 6-hour period was found between controls and patients with ulcerative colitis. Patients with Crohn's disease, celiac disease, or with rheumatoid arthritis were found to have significantly decreased urinary excretion of PEG 400. The results of this study indicate that there is no identifiable increase in intestinal permeation as measured by PEG 400 excretion during periods of active inflammatory disease.

Absorption of glucose from urinary conduits in diabetics and non-diabetics

The ability of urinary conduits to absorb glucose was investigated. A solution containing 1% glucose and the inert marker phenol red was put into conduits in diabetic and non-diabetic patients. Samples were withdrawn at intervals for analysis and the fall in concentrations plotted against time. The loops in the patients without diabetes did not absorb glucose, but glucose was absorbed in one of the three diabetics. Ileal loops in patients with diabetes may absorb urinary glucose. This should be checked in any diabetic with urinary diversion before advice is given on long term management. Routine testing of conduit urine for glucose may not be an adequate screen for diabetes in patients with urinary diversions.

Radiolabeled fiber: a physiologic marker for gastric emptying and intestinal transit of solids

We report here a study of radiolabeled cellulose as a marker for gastric emptying and intestinal transit of fiber in a dog model. A chemically stable radioisotopic label (131I) was employed to facilitate external monitoring of the tracer. 131I-labeled fiber was found to be biologically stable, since no iodine was absorbed during passage through the canine digestive system. In comparison with water-soluble tracers, gastric emptying of [131I]fiber is very slow. This is consistent with the expected behavior of fiber as a nondigestible solid. We anticipate this new radiolabeled marker will prove to be a useful tool for studies on gastric emptying, intestinal transit, fate and actions of dietary fiber in nonruminant experimental animals and, eventually, in man.

Extracellular space determination in rat small intestine by using markers of different molecular weights

The apparent extracellular space (ECS) of rat jejunum, everted and cannulated "in vitro", has been measured by using extracellular markers of different molecular weights. The markers used were two polyethyleneglycols, 14C and 3H labelled (14C-PEG MW 4000 and 3H-PEG MW 900) and 3H-sucrose. The ECSs for the mucosal and serosal sides have been separately determined throughout the time course, and it has been found that the two spaces are identical when PEG 4000 was used but the serosal ECS is almost the double when using PEG 900. The serosal ECS determined with sucrose is four times as big as the mucosal ECS. It seems reasonable to conclude that the best marker for the measure of total apparent ECS is sucrose, placed in the serosal compartment, taking into account that the mucosal ECS is four times smaller than the serosal one. All the markers used reach equilibrium with ECS, more rapidly in the mucosal than in the serosal ECS. Finally, by comparing cell water and cell Na concentrations, one observes that there is a statistical difference between the results obtained by using PEG 4000 as an extracellular marker and those obtained with sucrose.

The rat and hamster jejunum during transintestinal transport in vitro

By using the jejunal tract of rat and hamster intestine, net fluid transintestinal transport in the everted sac incubated in vitro at 28 degrees C and at 38 degrees C has been determined. In the scraped mucosa wet weight/dry weight ratio, cell water, sodium and potassium concentration have been detected in vivo and in vitro, throughout the incubation time, at the two different temperatures. Under all these conditions ATP, ADP and AMP levels have been determined in total intestine and in scraped mucosa. In rat jejunum incubated in vitro at 38 degrees C transintestinal fluid transport continuously decreases during 1-h experiment; in the same time the enterocyte gains sodium, dilutes cell potassium and swells, whereas its energy charge is dramatically reduced. All these parameters are constant in rat jejunum incubated at 28 degrees C and in the hamster incubated both at 28 degrees C and at 38 degrees C throughout the experiment. An inadequate diffusion of oxygen into the enterocyte, could tentatively explain experimental results obtained on rat jejunum at 38 degrees C. Under all tested conditions, energy charge and intracellular potassium are lower in conditions in vitro than in those in vivo; the contrary happens for cell sodium and swelling. The oxygenation of the intestine in vitro, lower than the one in vivo, could explain the different behaviour found in the two experimental conditions.

GI drug absorption in rats exposed to cobalt-60 gamma-radiation II: in vivo rate of absorption

The rate of absorption of sulfanilamide, bretylium tosylate, sulfisoxazole acetyl, and riboflavin was studied in rats exposed to 850 rad of cobalt-60 gamma-radiation either 1 or 5 days before oral drug administration. Polyethylene glycol 4000 was administered with sulfanilamide; its distribution along the GI tract indicated that the gastric emptying rate was reduced threefold at 1 day postirradiation but returned to normal at 5 days postirradiation; the small intestinal transit rate was not detectably altered by irradiation. At 1 day postirradiation, there was a marked decrease in the absorption rate of sulfanilamide, a smaller, although significant, decrease in the absorption rate of sulfisoxazole acetyl and bretylium, and an increase in the absorption rate of riboflavin. At 5 days postirradiation, the drug absorption rate was normal. The changes in the absorption rate of the drugs were due to a radiation-induced reduction in the gastric emptying rate; the permeability of the GI epithelium did not appear to be affected by radiation. The results indicate that, immediately following irradiation, a marked reduction in the gastric emptying rate causes a pronounced reduction in the absorption rate of rapidly absorbed drugs, a less pronounced reduction in the absorption rate of drugs that are absorbed slowly because of slow dissolution or slow diffusion across the GI epithelium, and an increase in the absorption rate of drugs that are absorbed by a saturable mechanism provided the mechanism is not impaired by irradiation.

Energy-rich phosphates and transintestinal transport in rat intestine incubated in vitro at different temperatures

In the present work, the transported fluid and the tissue content of ATP, ADP and AMP has been evaluated in the jejunum rat intestine which was everted and incubated in vitro both at 28 degrees C and at 38 degrees C for 1 h. The energy-rich phosphates have been measured in the tissue at the beginning and at the end of the experiment as well as in vivo. These determinations have been made in the total intestine and in the scraped mucosa. ATP and ADP content are higher in vivo and lower but constant at 28 degrees C in vitro; on the contrary, at 38 degrees C in vitro, the initial and final content of these adenilic nucleotides are both lower than at 28 degrees C. Under all these conditions the AMP content does not vary appreciably. Wet weight to dry weight ratios ahve been reported for mucosal and submucosal tissues in unincubated and incubated intestines. In some experiments, fluid transport (measured as an actual serosal volume increase) was determined every 20 min during a 1-h incubation. At 28 degrees C, fluid transport is constant throughout the time of the experiment, but at 38 degrees C, there is a progressive decrease of the transported fluid. Fluid transport and ATP content of the intestine seem to be directly related. The transport activity which is lower at 38 degrees C than at 28 degrees C, seems to be due to a low availability of energy-rich phosphates.

Salt and water permeability of the epithelium of the coprodeum and large intestine in the normal and dehydrated fowl (Gallus domesticus). In vivo perfusion studies

1. The transmural net flow of salt and water in the coprodeum and large intestine of normal and dehydrated hens was investigated by means of an intraluminal in vivo perfusion technique.2. The lumen was perfused with a raffinose-electrolyte solution having a low sodium concentration (Na(+) = 1 m-equiv/l.). The osmolality of the solution was adjusted in the range 66-585 m-osmolal by adding raffinose. Polyethylene glycol 4000 (PEG) served as a water marker. The experiments permitted estimation of the passive transport parameters: the reflexion coefficient (sigma) of the penetrating solutes (predominantly NaCl), the Na(+) mobility (omega(s)), and the osmotic water permeability coefficient (P(osm)).3. When the luminal fluid had the same osmolality as plasma the net water flow (J(v)) was zero, indicating a sigma of unity. The net flow of Na(+) was zero, (at J(v) = 0) and a transmural electric potential difference close to zero was present both in normal and in dehydrated birds. This indicates an omega(s) of zero. When lumen osmolality was higher than that of plasma, no ;solvent drag' effect on Na(+) was demonstrated in the serosa to mucosa (s-m) direction.4. The P(osm) appeared to be independent of the luminal osmolality in the range of +/-200 m-osmolal from plasma osmolality. In normal birds the P(osms-m) was 3.2 mul./kg.hr.m-osmolal, the P(osmm-s) 5.8 mul./kg.hr.m-osmolal. In dehydrated birds these values were 3.6 and 10.0 respectively. Thus there seems to be rectification of water flow, and it varies with the state of hydration.5. A net K(+) flow of 15-50 mu-equiv/kg.hr in the m-s direction and a net Cl(-) flow of 10-50 mu-equiv/kg.hr in the s-m direction were observed. No relationship was observed between the flow of these solutes and the net water flow.