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At least 883 records · Page 49Linked to original sources
PubMed1991

Intestinal absorption of gabapentin in rats.

Gabapentin (1-aminomethyl-)cyclohexaneacetic acid, Gö 3450, CI-945; CAS 60142-96-3) is a new gamma-aminobutyric acid (GABA) analogous compound that has shown an anticonvulsive effect as well as low toxicity in preclinical and clinical studies. The substance is well absorbed after oral administration and penetrates the blood-brain barrier. The aim of experiments was to study the mechanism of intestinal absorption, the relationship between the absorption rate and the applied concentration and whether the absorption rate differs between different parts of the intestine. For this purpose, isolated intestinal segments of rats (everted sac preparations) were used. Due to the fact that gabapentin is not metabolized in the intestine, its concentration in the mucosal and serosal compartments could be determined by scintillation counting of 3H-gabapentin. The results showed that gabapentin was absorbed by simple diffusion because neither indications for an uphill nor for a carrier-mediated transport could be demonstrated. The absorption rate was linearly related in the concentration range from 0.001 to 100 mmol/l. There was no significant difference between the absorption rate in the three parts of the small intestine at 1 and 10 mmol/l, while the absorption rate was significantly (p less than 0.01) lower in the colon.

Acetates↗
PubMed1982

Intestinal absorption of several beta-lactam antibiotics. IV. Binding to the various components in the intestinal mucosa of rat and role in absorption process.

The binding characteristics of zwitterionic and monobasic beta-lactam antibiotics to the components in the intestinal mucosa of rat was investigated. From the binding experiments using the brush border membrane preparation and the insoluble cellular fractions, there was no correlation between the binding behavior and the absorption characteristics. However, there was a highly significant correlation between the affinity to the soluble F1 fraction and the absorption characteristics of these antibiotics. It was also found that the binding of these antibiotics to the other soluble protein fractions were significantly smaller than that to F1 fraction. It was postulated that the binding properties of these antibiotics to soluble F1 fraction play an important role in the absorption process.

Animals↗
PubMed2000

Effect of magnesium supplementation on the fractional intestinal absorption of 45CaCl2 in women with a low erythrocyte magnesium concentration.

The cosupplementation of magnesium with calcium has been suggested to be beneficial in the prevention of osteoporosis. We investigated the effect of magnesium supplementation on parameters of bone resorption and fractional 45Ca absorption. Twenty apparently healthy women with a mean age of 39.2 +/- 9.2 years and an erythrocyte magnesium concentration less than 1.97 mmol/L were recruited into a controlled magnesium supplementation trial. During weeks 1 to 4, they received a daily control preparation, potassium/sodium citrate malate (PSCM). During weeks 5 to 8, the subjects received magnesium citrate malate (MCM) equivalent to 250 mg magnesium per day. During the fourth and eighth weeks, blood was collected for measurement of the serum intact parathyroid hormone (PTH) concentration and serum and erythrocyte magnesium concentration. Urine was collected for measurement of calcium, magnesium, creatinine, and deoxypyridinoline excretion. On the final day of each treatment period, 5 microCi45CaCl2 was administered orally, and the isotope was traced in the blood and urine over 7 hours. Urinary calcium, 45Ca, and deoxypyridinoline excretion, as well as serum intact PTH levels, showed no statistically significant changes as a result of magnesium supplementation. However, urinary magnesium excretion increased by 31.1% (P < .005) while fractional 45Ca absorption decreased by 23.5% (P < .001) as a result of magnesium supplementation. It is concluded that magnesium supplementation does not result in changes in bone resorption, while the fractional intestinal absorption of 45Ca appears to decrease.

Adult↗
PubMed1981

Reduced intestinal absorption of vitamin E by low dietary levels of retinoic acid in rats.

It was observed that rats fed a low dietary level of retinoic acid had markedly lower plasma concentrations of alpha-tocopherol than did rats fed the same amount of retinol. In this report, the possible mechanisms by which retinoic acid alters vitamin E metabolism has been investigated. Weanling male rats were fed a complete purified diet with either retinol or retinoic acid at 4 mg/kg diet; plasma and tissues were analyzed after 2-5 weeks. The plasma alpha-tocopherol concentration in rats ingesting retinoic acid was one-half that of rats ingesting retinol, and this difference also occurred in the liver and adipose tissue. Similar effects occurred in chicks. This low dietary level of retinoic acid had no effect on plasma triglyceride concentration, as has been reported for higher intakes, and plasma cholesterol and total lipids were also unaffected. Retinoic acid did not affect the rate of decrease in endogenous alpha-tocopherol in normal rats fed a vitamin E-free diet for 3 weeks. In rats with mesenteric lymph cannulas, dietary retinoic acid caused a reduced absorption of 3H-labeled alpha-tocopherol. In chicks fed retinoic acid, plasma and liver radioactivity 2.5 hours after an oral dose of 3H-alpha-tocopherol was one-fifth that of chicks fed retinol. More oxidation of alpha-tocopherol occurred during absorption in rats fed retinoic acid than in those fed retinol, as evidenced by more alpha-tocopherylquinone in the collected lymph. We postulate that dietary retinoic acid reduces the intestinal absorption of alpha-tocopherol and may also promote its oxidation.

Animals↗
PubMed1984

Effects of atropine and guanethidine on canine intestinal absorption and blood flow.

The possibility of tonic autonomic control over intestinal Na and H2O absorption and whether the cardiovascular system was involved was tested by administration of atropine or guanethidine. 3H2O and 22Na in saline perfused through the lumen were used to calculate unidirectional fluxes and total and absorptive site blood flow in canine ileum. Both atropine and guanethidine had qualitatively similar effects on absorption and blood flow with atropine being quantitatively greater. Net Na and H2O absorption were not increased significantly but their absorptive and secretory unidirectional fluxes were increased significantly. Total blood flow was not affected but absorptive site blood flow was increased and resistance decreased. The absorptive site blood flow was correlated with the absorptive Na fluxes similarly in all groups. The secretory fluxes of Na and H2O were correlated with estimated capillary pressure when all three groups were considered together. It was concluded that there is tonic cholinergic control over intestinal absorption which is mediated, in part, through cardiovascular effects. The findings were consistent with tonic parasympathetic activity having primarily a direct effect on gut absorption and blood flow but tonic sympathetic activity primarily modulating the direct effects of other regulatory mechanisms.

Animals↗
PubMed2003

Role of P-glycoprotein in the intestinal absorption and clinical effects of morphine.

INTRODUCTION: There is considerable and unexplained individual variability in the morphine dose-effect relationship. The efflux pump P-glycoprotein regulates brain access and intestinal absorption of numerous drugs. Morphine is a P-glycoprotein substrate in vitro, and P-glycoprotein affects morphine brain access and pharmacodynamics in animals. However, the role of P-glycoprotein in human morphine disposition and clinical effects is unknown. This investigation tested the hypothesis that plasma concentrations and clinical effects of oral and intravenous morphine are greater after inhibition of intestinal and brain P-glycoprotein, with the P-glycoprotein inhibitor quinidine used as an in vivo probe. METHODS: Two randomized, double-blind, placebo-controlled, balanced crossover studies were conducted in normal healthy volunteers after institutional review board-approved informed consent was obtained. In the first protocol, pupil diameter was evaluated after intravenous morphine administration (0.15 mg/kg), 1 hour after oral quinidine or placebo. In the second protocol, plasma morphine and glucuronide metabolite concentrations and pupil diameters were evaluated after oral morphine administration (30 mg), dosed 1 hour after oral quinidine (600 mg) or placebo. RESULTS: Quinidine had no effect on intravenous morphine effects (time to maximum miosis, maximum effect, or area under the curve [AUC] of miosis versus time). Quinidine increased the oral morphine maximum plasma concentration (31.8 +/- 14.9 ng/mL versus 16.9 +/- 7.4 ng/mL, P <.05) and AUC (65.1 +/- 21.5 versus 40.8 ng. h. mL(-1) +/- 14 ng. h. mL(-1), P <.05) but had no effect on elimination rate. Plasma morphine glucuronide concentrations were unchanged; however, the morphine glucuronide/morphine ratios were diminished by quinidine. Differences in oral morphine miosis (AUC, 16.8 +/- 9.3 mm. h versus 10.8 +/- 6.5 mm. h; P <.05) were commensurate with changes in plasma morphine concentration, and concentration-effect relationships were unchanged. Quinidine altered subjective self-assessments of oral but not intravenous morphine effects. DISCUSSION: Quinidine increased the absorption and plasma concentrations of oral morphine, suggesting that intestinal P-glycoprotein affected the absorption, bioavailability, and, hence, clinical effects of oral morphine. However, quinidine had no effect on morphine concentration-effect relationships, suggesting that if quinidine is an effective inhibitor of brain P-glycoprotein then P-glycoprotein did not appear to have a significant effect on brain access of morphine.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2003

Factors affecting intestinal absorption of highly lipophilic food microconstituents (fat-soluble vitamins, carotenoids and phytosterols).

Highly lipophilic food microconstituents (HLFMs) with octanol-water partition coefficients log10 P(c) > 8 include the fat-soluble vitamins (A, E, D and K) and phytochemicals with potential health benefits, the carotenoids and phytosterols. It has been assumed that these compounds have the same metabolism in the human upper gastrointestinal tract and that they follow the same fate as lipids. However, a literature review shows that the metabolism of HLFMs in the upper gastrointestinal tract depends on each HLFM species. For example, some HLFM esters are hydrolyzed mainly by pancreatic lipase, others by bile salt-stimulated lipase; some HLFMs are apparently absorbed by passive diffusion, others by a transporter. Also, although some factors (HLFM molecular species, fat, food matrix) affect absorption efficiency of most HLFMs, other factors (fibers, microconstituents) apparently affect absorption only of some HLFMs. The mnemonic acronym SLAMENGHI, previously proposed to list the factors affecting the bioavailability of carotenoids, was used here to review current knowledge of the factors suspected to affect the intestinal absorption of HLFMs. The available data reveal numerous gaps in the knowledge of the metabolism of HLFMs and the factors that affect their absorption. These gaps need to be filled to be able to formulate HLFMs so as to promote greater absorption efficiency.

Age Factors↗
PubMed1997

Intestinal absorption of captopril and two thioester analogs in rats and dogs.

The objectives of this study were (i) to determine whether the reduced absorption of captopril from the colon of humans also occurs in rats and (ii), after confirmation of the relevance of a new rat model, to evaluate the intestinal absorption of captopril and several of its analogs. A model was developed and validated in which specific sites within the GI tract of rats were surgically implanted with a cannula such that animals could be dosed while conscious and unrestrained. The absorption of captopril after administration into the lower GI tract of rats was significantly reduced relative to the upper GI tract, which was consistent with results reported previously in humans. In rats, the absorption of the S-benzoyl thioester prodrug of captopril (SQ-25868) from the lower GI tract was substantially greater than that of captopril. However, the absorption of the S-benzoyl thioester prodrug of 4-phenyl thio-captopril (SQ-26991) from the lower GI tract was only marginally better than that of captopril. In additional studies in dogs, a 12h controlled-release formulation of SQ-25868 provided sustained blood levels of captopril while maintaining acceptable bioavailability (> 80%). Two approaches were tried, without success, to stabilize captopril in vivo: (i) complexation with zinc (SQ-26284) and (ii) use of ascorbic-acid-buffered (pH 3.5) vehicle. The zinc complex might have failed because it has very low solubility, whereas the pH-3.5-buffered vehicle was quickly neutralized within the colonic lumen in rats, and did not stabilize captopril against oxidation. Rapid neutralization might explain why the colonic bioavailability of captopril was not substantially increased when this pH-3.5-buffered vehicle was tried in humans.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1987

Utilizing bile acid carrier mechanisms to enhance liver and small intestine absorption.

On the basis of the enterohepatocycling phenomenon of bile acids involving the intestines, liver, and gallbladder, it was conceptualized that bile acids could serve as a molecular carrier of drugs by taking advantage of the bile acid active transport mechanism. It was further proposed that derivatization or analogation of bile acids at the C3-OH position was the desired route because of the reactive hydroxyl group and, moreover, because of the active transport requirement of retaining the C17 side chain with a single terminal acidic function. Using 3-tosylcholic, 3-benzoylcholic, and 3-iodocholic acids, in situ liver absorption, biliary excretion, and intestinal absorption studies in the rat were successful in establishing the concept that C3-derivatives and analogs of bile acids are, potentially, novel molecular delivery systems for intestinal and liver-site directed absorption.

Algorithms↗
PubMedDate not supplied

Feature selection for descriptor based classification models. 2. Human intestinal absorption (HIA).

We show that the topological polar surface area (TPSA) descriptor and the radial distribution function (RDF) applied to electronic and steric atom properties, like the conjugated electrotopological state (CETS), are the most relevant features/descriptors for predicting the human intestinal absorption (HIA) out of a large set of 2934 features/descriptors. A HIA data set with 196 molecules with measured HIA values and 2934 features/descriptors were calculated using JOELib and MOE. We used an adaptive boosting algorithm to solve the binary classification problem (AdaBoost.M1) and Genetic Algorithms based on Shannon Entropy Cliques (GA-SEC) variants as hybrid feature selection algorithms. The selection of relevant features was applied with respect to the generalization ability of the classification model, avoiding a high variance for unseen molecules (overfitting).

Humans↗
PubMed1985

Effects of acute and chronic treatment with glucocorticoids on the intestinal absorption of calcium and phosphate and on plasma 1,25-dihydroxyvitamin D levels in pigs.

We have used young pigs, each prepared surgically with a Thiry-Vella loop of proximal small intestine, to study the time course of changes in the intestinal absorption of calcium, phosphate, sodium, glucose and water and on the plasma levels of 1,25-dihydroxyvitamin D after treatment of the animals with glucocorticoids. Perfusion of the intestinal loop for 6 h with a solution containing hydrocortisone or beta-methasone was without effect on the absorption of calcium or phosphate. The oral administration of betamethasone stimulated the absorption of calcium and phosphate by 15-20% for 2-3 days before the trend was reversed and absorption was progressively reduced. Chronic treatment with betamethasone inhibited only the active component of calcium and phosphate absorption. Treatment with betamethasone was associated with a sustained 25-50% increase, to a maximum by 2 days, in the absorption of sodium, glucose and water. Plasma levels of 1,25-dihydroxyvitamin D were reduced within 2 days of the start of treatment and reached a minimum (40-50% decrease) in 4-6 days. We conclude that the initial stimulation of calcium and phosphate absorption is caused by the increased absorption of water. The long-term decrease in absorption may not be caused solely by the decreased circulating levels of 1,25-dihydroxyvitamin D since absorption continued to fall for several weeks after 1,25-dihydroxyvitamin D levels had reached a minimum.

Animals↗
PubMed1986

Intestinal absorption of sodium cefoxitin in rats: effect of formulation.

The absorption of cefoxitin from rat intestine, rectum and small intestine was greater when the powdered form was administered than when an aqueous solution was given. Cefoxitin absorption from the small intestine was significantly increased after its administration in suppository form prepared with a triglyceride base, although rectal absorption from the suppository did not differ from that of the drug in powdered form. The increase in absorption by the small intestine from the suppository form may be due to fatty acids produced from triglyceride by lipase.

Animals↗