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PubMedDate not supplied

Absorption of amino acids in different parts of the small intestine in growing pigs. I. Absorption of free amino acids and water.

The study was on pigs weighing 50-75 kg with temporarily isolated loops of the proximal, middle and terminal small intestine. Isolated segments were perfused with solutions of acid hydrolysate of casein containing 8, 12 or 16 g free amino acids per litre. The capacity to absorb water increased along the small intestine reaching about 5 1/m/24 h in the distal part. The absorption of nitrogen from all solutions was least in the proximal small intestine (up to 8 g/m/24 h); there were no significant difference in nitrogen absorption between the other parts. The rates of absorption of various amino acids, were different and depended on the concentration of amino acids in the intestine. On the whole, the rates of absorption of essential amino acids were: Arg, Met, Ile, Leu greater than lys greater than Thr, His. From among the non-essential amino acids Glu and Gly were absorbed to the lesser extent than the other ones.

Amino Acids↗

PubMed1993

Studies on the reliability of a novel absorption-lipophilicity approach to interpret the effects of the synthetic surfactants on drug and xenobiotic absorption.

Some theoretical principles of the absorption/lipophilicity approach, which attempts to explain the effects of the synthetic surfactants on xenobiotic and drug intestinal absorption, are reviewed and experimentally checked by examining the correlations obtained between "in situ" absorption constants, ka, found in rat colon, and "in vitro" lipophilicity indexes, K', for two compound series (secondary aliphatic amines and phenylalkylamines) in the absence and in the presence of the nonionic surfactant Polysorbate 80, in the intestinal perfusion fluid. Evidence is given for the following actions of the synthetic surfactant: at its critical micelle concentration (CMC), it increases the polarity of the absorbing membrane and, at the same time, it disrupts the aqueous stagnant diffusion layer adjacent to the mucosal barrier. When a supramicellar concentration (SMC) is used, the above actions are almost totally masked by the micellar solubilization of the tested amines, which decreases their absorption constants relative to those found at CMC, as markedly as solute lipophilicity increases. As a consequence of these actions, the correlations between ka and K', which are clearly hyperbolic in free solution, become potential in the presence of the surfactant at its CMC, whereas at SMC a bilinear correlation is obtained. Absorption via lipophilic ionized species seems to take place for both compound series. Mathematical and physicochemical interpretations of this behaviour are outlined, and biopharmaceutical implications of these phenomena are discussed.

Amines↗

PubMed1997

Nonlinear intestinal absorption of 5-hydroxytryptamine receptor antagonist caused by absorptive and secretory transporters.

The mechanism of the nonlinear concentration dependence of intestinal absorption of the 5-hydroxytryptamine receptor antagonist azasetron was studied by use of rat in situ intestinal perfusion, as well as an in vitro Ussing-type chamber method mounted with rat intestinal tissue and cultured monolayers of human adenocarcinoma Caco-2 cells. The intestinal absorption rate constant of azasetron evaluated by the Doluisio method increased significantly with increasing concentration of azasetron up to 10 mM in a nonlinear fashion and tended to decrease at higher concentrations. Mucosal-to-serosal directed permeation of [14C]azasetron across rat ileal sheets evaluated by the in vitro Ussing-type chamber method also increased in a nonlinear fashion in a low concentration range, followed by a decrease as the concentration was further increased, whereas serosal-to-mucosal directed permeation decreased in a concentration-dependent manner. Vectorial transport of [14C]azasetron across a Caco-2 cell monolayer was observed, with higher transport in the basolateral-to-apical direction at a trace concentration of azasetron. When the initial uptake rate of azasetron by Caco-2 cells was measured, it was saturable with an apparent half-saturation concentration of 15 mM and was reduced in the presence of several cationic compounds. These observations suggest that azasetron is taken up by a carrier-mediated transport mechanism across the intestinal epithelial cells. When the steady-state uptake of [14C]azasetron was measured, it was increased in the presence of unlabeled azasetron and ondansetron. In addition, the steady-state uptake was enhanced in the presence of a P-glycoprotein inhibitor, cyclosporin A, and by ATP-depletion of the cells, although these treatments had no effect on the initial uptake of [14C]azasetron. Furthermore, the multidrug-resistant cancer cell line K562/ADM that overexpresses P-glycoprotein accumulated azasetron less extensively than did the parental drug-sensitive K562 cells. These results strongly suggest that azasetron is secreted into the intestinal lumen predominantly by P-glycoprotein. We conclude that intestinal transport of azasetron involves specialized transporters in both the absorptive and secretory directions, and the complex nonlinear intestinal absorption characteristics can be ascribed to the participation of multiple transport mechanisms.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1996

Ligation of the iron in the heme-heme oxygenase complex: X-ray absorption, electronic absorption and magnetic circular dichroism studies.

Heme oxygenase (HO) catalyzes the first steps in the breakdown of heme to biliverdin and carbon monoxide. It is a membrane-bound protein that has been shown to exist in two isoforms, HO-1 and HO-2. Recently, a soluble, truncated form of rat HO-1 (rHO) lacking the 23 amino-acid membrane anchor has been expressed in E. coli. Extended X-ray absorption fine structure (EXAFS) data on ferric rHO and its fluoride derivative support assignment of the axial iron ligands as oxygen and/or nitrogen donors having distances similar to ferric myoglobin. The electronic absorption and magnetic circular dichroism (MCD) spectra of the ferric and ferrous protoheme complexes of rHO as well as various ligand adducts are very similar to the corresponding spectra of myoglobin. The present study is the first investigation of the heme-heme oxygenase complex with EXAFS and MCD spectroscopy and establishes that the proximal ligand to the heme in rHO is histidine. Furthermore, the close similarity between the electronic absorption and MCD spectra of ferric rHO and myoglobin over the pH range 6 to 10 is consistent with distal heme ligation of ferric rHO as a water molecule or hydroxide ion, depending on pH. Taken together and in conjunction with the results of earlier studies, EXAFS, electronic absorption, and MCD spectroscopy solidly establish that the ligands to the heme in rHO are identical to those in myoglobin, namely, histidine/H2O at low pH and histidine/OH at high pH.

Animals↗

PubMedDate not supplied

Determination of self-absorption corrections for gamma analysis of environmental samples: comparing gamma-absorption curves and spiked matrix-matched samples.

Accurate determination of the massic activity of gamma-emitting radionuclides in environmental samples, particularly sediments and soils, cannot be achieved without taking into account sample self-absorption. The extent of self-absorption in the sample will depend on a number of factors including sample composition, density, sample size and gamma-ray energy. The preferred method for correcting for this effect is to use spiked or natural matrix reference materials that match each sample type to be analysed. However, for laboratories that must measure a wide variety of sample matrices this method is too costly and time-consuming. Another technique commonly used is to make direct gamma-ray transmission measurements for each sample. This method, while more practical, still requires a minimum of three measurements to be made for each sample analysed. A more convenient method is to prepare sets of gamma-absorption curves. This approach involves making a series of direct transmission measurements for samples of varying densities but similar type. Sets of matching samples, both spiked and unspiked, were prepared and density correction factors determined using the direct transmission method and the spiked sample approach. It was found that, for soil and sediment samples, these two methods typically differed by 5-9% for higher energy gamma rays and by 12-15% for the 59.54 keV 241Am peak. Gamma-absorption curves were also derived and, for the admittedly limited dataset, 95% confidence intervals of +/-7% for the curve generated using the spiked samples method were obtained.

Calibration↗

PubMed1999

A compartmental absorption and transit model for estimating oral drug absorption.

This report describes a compartmental absorption and transit model to estimate the fraction of dose absorbed and the rate of drug absorption for passively transported drugs in immediate release products. The model considers simultaneous small intestinal transit flow and drug absorption. Both analytical and numerical methods were utilized to solve the model equations. It was found that the fraction of dose absorbed can be estimated by F(a) = 1-(1+0.54 P(eff))(-7), where P(eff) is the human effective permeability in cm/h. A good correlation was found between the fraction of dose absorbed and the effective permeability for ten drugs covering a wide range of absorption characteristics. The model was able to explain the oral plasma concentration profiles of atenolol.

Adsorption↗

PubMed2004

Quartz crystal microbalance and infrared reflection absorption spectroscopy characterization of bisphenol A absorption in the poly(acrylate) thin films.

The absorption process of bisphenol A (BPA) in a number of poly(acrylate) thin films, such as poly(2-methoxyethyl acrylate) (PMEA), poly(ethyl acrylate) (PEA), poly(n-butyl methacrylate) (PBMA), and poly(methyl methacrylate) (PMMA), has been investigated by quartz crystal microbalance (QCM) and infrared reflection absorption spectroscopy (IRRAS) measurements. Both QCM and IRRAS measurements show that the BPA molecules absorb in PMEA, PEA, and PBMA thin films but not in PMMA thin film. The differences in the BPA absorption behavior are mainly attributed to the difference in the glass transition temperature (T(g)) between these polymers. This absorption behavior also depends on the BPA concentration and polymer film thickness. Furthermore, IRRAS characterization demonstrates that the hydrogen bonding is formed between the hydroxyl group in BPA and the carbonyl group in the poly(acrylate) thin films. BPA molecule absorbed in these polymer thin films can be removed by ethanol rinse treatment. By optimizing experimental conditions for the QCM electrode modified by PMEA thin film, detection limitation of approximately 1 ppb for BPA can be realized by the in situ QCM measurement. This method is expected to be a sensitive in situ detection way for trace BPA in the environmental study.

Journal Article↗

PubMed2006

Two-photon absorption strength: a new tool for the quantification of two-photon absorption.

In this paper, we define the two-photon absorption strength, a new characterization tool, similar to the oscillator strength, but for two-photon absorption. It allows the quantification of the two-photon absorption properties of molecular systems which are one-photon transparent. Its definition is such that the corresponding numerical values are around 100 for small molecules. We also show that this new theoretical tool allows the direct comparison of experimental and theoretical data without requiring the introduction of any arbitrary band width. As an example, the experimental and theoretical (AM1+CNDOS and HF+CIS3-21G) two-photon absorption properties of the 2,2'-bi(9,9-dihexylfluorene) molecule are compared.

Journal Article↗

PubMed1967

Selective inhibition of absorption and long distance transport in relation to the dual mechanisms of ion absorption in maize seedlings.

The influence of several uncouplers of oxidative phosphorylation and inhibitors of terminal electron transport was studied on absorption and long distance transport of both K and C1 at concentrations within each range of the dual isotherm typical of ion uptake by maize roots. At low concentrations in the range of system 1, the system considered to implement ion movement through the plasma membrane, root absorption and long distance transport are equally inhibited by a given inhibitor. In the high range of system 2, the system considered to mediate ion passage through the tonoplast, long distance transport is markedly less sensitive to inhibitors than is absorption. The observations are in accord with the hypothesis that only system 1 is involved in the uptake of ions from the external solution into the symplast, and hence into the xylem. At high concentrations, entrance into the symplasm is deemed to be largely by diffusion and therefore less inhibitor sensitive. With respect to absorption by the roots, the plasma membrane system is more inhibitor sensitive than is the tonoplast system. It is suggested that the difference in sensitivity is real, and not the consequence of an inequality of inhibitor concentration in the vicinity of the plasma membrane and tonoplast respectively.

Biological Transport↗

PubMed1977

The absorption of phenformin and its effects on glucose and water absorption in isolated perfused rat small intestine.

The effects of phenformin on glucose and water absorption from isolated perfused rat small intestine were studied. Luminal phenformin inhibited glocose and water absorption progressively as its concentration was increased from 0-1-1-0 mg.ml-1. At 0-5 mg phenformin ml-1, inhibition increased with time of exposure to phenformin up to 15 min and thereafter remained constant. Arterial infusion of phenformin (1-0 mg-ml-1) produced less inhibition of glucose and water absorption. The site of phenformin's action appeared to be intracellular. Phenformin absorption from a luminal perfusate (0-5 mg-ml-1) was measured. Although it was rapidly absorbed (22 microgram.cm intestine-1.h-1) from the lumen, less than 2 microgram.cm-1.h-1 appeared at the serosal surface of the intestine. In subsequent phenformin-free perfusion, only 25% of the absorbed phenformin was recovered in the luminal and serosal effluents.

Animals↗

PubMed2002

Analysis and prediction of absorption behavior for theophylline orally administered as powders based on gastrointestinal-transit-absorption (Gita) model.

Absorption behavior of theophylline, categorized into Class I of Biopharmaceutics Classification System, orally administered as powders in rats was analyzed and predicted by Gastrointestinal-Transit-Absorption (GITA) model, which was modified to describe GI-transit kinetics and dissolution of powders orally administered. First of all, GI-transit kinetics of glass beads was examined to describe the transit kinetics of powders through GI tract in rats. The results showed that the gastric emptying of glass beads was slower than that of solution, but that there was not much difference in the transit rate constants through the small intestine and cecum between glass beads and solution. Furthermore, to introduce the dissolution process of theophylline powders into GITA model, an in-vitro dissolution test was examined for theophylline powders according to the Japanese Pharmacopoeia paddle method. The dissolution rate constants calculated based on the mean dissolution time were not so different in the range of pH from 1.2 to 6.5. Using the parameters for GI transit, dissolution and absorption obtained, the plasma concentration-time profile of theophylline after oral administration as powders to rats was predicted based on GITA model. The profile calculated was significantly correlated with the observed time course of plasma concentration for theophylline, and the parameters such as C(max) and AUC based on the predicted curve coincided with those on the observed data, showing that GITA model is useful for the prediction of the absorption behavior of drugs administered as powders. The simulation studies showed that about 80% of orally administered theophylline powders dissolved in the stomach and that the remaining powders rapidly moved to the lower jejunum and ileum, where they dissolved. Furthermore, it was suggested that theophylline is absorbed mostly in the upper small intestine, duodenum, upper jejunum and lower jejunum, after its oral administration as powders.

Journal Article↗

PubMed2000

Absorption enhancement of a protein drug by nitric oxide donor: effect on nasal absorption of human granulocyte colony-stimulating factor.

The objective of this study was to evaluate the effect of a nitric oxide (NO) donor, S-nitroso-N-acetyl-DL-penicillamine (SNAP), on the nasal absorption of recombinant human granulocyte colony-stimulating factor (rhG-CSF) in rabbits and to evaluate the irritation (cytotoxicity) potential of the NO donor on the mucosal membrane using a cultured cell system (strain KB, human epidermoid carcinoma of the floor of the mouth). Significantly higher serum G-CSF concentration and increased total leukocyte count in the peripheral blood were observed after coadministration of rhG-CSF (100 microg/kg) with SNAP at various doses (0.3-3.3 mg/kg). The serum G-CSF concentration and the increased total leukocyte count were markedly decreased by the presence of the NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazole-1-oxyl 3-oxide sodium salt (carboxy-PTIO), in combination with rhG-CSF and SNAP. However, no significant inhibitory effect of glutathione (peroxynitrite scavenger) on the absorption-enhancing effect of SNAP was observed. These results suggest that carboxy-PTIO inhibits the absorption-enhancing effect of NO released from SNAP. We found that SNAP has a very low potential for cytotoxicity, as evaluated by the cell detachment assay, release of lactate dehydrogenase (LDH) from cultured cells and morphological observations of nasal tissue of rabbits. It is concluded that a NO donor such as SNAP is a promising absorption enhancer for nasal protein-drug delivery.

Administration, Intranasal↗

PubMed1999

[Background absorption and its correction in the determination of Co in steel with flame atomic absorption spectrometry].

In this paper, a study of background absorption and interference of Fe in the determination of Co with flame atomic absorption spectrometry was done. The influence of background absorption on Co 240.7 nm could be completely eliminated when Au 242.8 nm was used as a background correction line, and the results of the determination of micro-amount Co in iron and high-alloy steel with standard addition method were satisfactory. The mechanism of background absorption and interference was also discussed.

English Abstract↗

PubMed1992

Characterization of the oral absorption of several aminopenicillins: determination of intrinsic membrane absorption parameters in the rat intestine in situ.

The absorption mechanism of several penicillins was characterized using in situ single-pass intestinal perfusion in the rat. The intrinsic membrane parameters were determined using a modified boundary layer model (fitted value +/- S.E.): Jmax* = 11.78 +/- 1.88 mM, Km = 15.80 +/- 2.92 mM, Pm* = 0, Pc* = 0.75 +/- 0.04 for ampicillin; Jmax* = 0.044 +/- 0.018 mM, Km = 0.058 +/- 0.026 mM, Pm* = 0.558 +/- 0.051, Pc* = 0.757 +/- 0.088 for amoxicillin; and Jmax* = 16.30 +/- 3.40 mM, Km = 14.00 +/- 3.30 mM, Pm* = 0, Pc* = 1.14 +/- 0.05 for cyclacillin. All of the aminopenicillins studied demonstrated saturable absorption kinetics as indicated by their concentration-dependent wall permeabilities. Inhibition studies were performed to confirm the existence of a nonpassive absorption mechanism. The intrinsic wall permeability (Pw*) of 0.01 mM ampicillin was significantly lowered by 1 mM amoxicillin and the Pw* of 0.01 mM amoxicillin was reduced by 2 mM cephradine consistent with competitive inhibition.

Absorption↗

PubMedDate not supplied

Intestinal absorption of 14C from 14C-phenanthrene, 14C-benzo[a]pyrene and 14C-tetrachlorodibenzo-para-dioxin: approaches with the Caco-2 cell line and with portal absorption measurements in growing pigs.

The aim of this work was to study the transfer through the intestinal barrier of two polycyclic aromatic hydrocarbons (PAHs) (benzo[a]pyrene and phenanthrene) and a dioxin (2,3,7,8-tetrachlorodibenzo-para-dioxin) which differed in their physicochemical properties. Both in vitro and in vivo assays were performed. For the in vitro study, Caco-2 cells, cultivated on permeable filters, permitted to measure the transepithelial permeability of the studied 14C-labelled molecules. For the in vivo study, portal absorption kinetics were evaluated in pigs fed contamined milk. The results showed that all the molecules were absorbed and demonstrated a differential intestinal absorption for the studied molecules. Phenanthrene appeared to be the fastest and most uptaken compound, followed by benzo[a]pyrene and finally 2,3,7,8-tetrachlorodibenzo-para-dioxin. Their absorption levels were respectively 9.5, 5.2 and 1.4% after a 6 h-exposure in vitro and 86.1, 30.5 and 8.3% in vivo for the 24 h following ingestion. These findings suggest that the physicochemical properties of the xenobiotics and intestinal epithelium play key roles in the selective permeability and in the bioavailability of the tested micropollutants.

Absorption↗

PubMed1997

Oral absorption of anti-aids nucleoside analogues: 3. Regional absorption and in vivo permeability of 2',3'-dideoxyinosine in an intestinal-vascular access port (IVAP) dog model.

The absolute oral and regional intestinal bioavailabilities (BAs) and pharmacokinetics (PK) of 2',3'-dideoxyinosine (ddI), a nucleoside analog used in the treatment of human immunodeficiency virus (HIV) infection, were investigated in an in vivo intestinal-vascular access port (IVAP) dog model. The mean (+/- SD) absolute regional intestinal BAs of ddI were 49.6 +/- 8.8, 42.7 +/- 7.9, and 13.6 +/- 5.4% after the bolus administration of unbuffered solutions containing 250 mg ddI into the duodenum, ileum, and colon of IVAP beagle dogs, respectively. The BA of the orally administered Videx 250 mg buffered chewable tablets was 44.9 +/- 1.6%. ddI absorption and disposition PK were modeled by simultaneously fitting intravenous, oral, and intestinal plasma level versus time data using a physiologically based PK model. The region-specific apparent absorption rates followed the rank order duodenum > ileum > colon. Apparent regional in vivo intestinal permeabilities correlated well with previously determined regional permeabilities in rats. The intestinal pH was monitored using a radiotelemetric pH monitoring system since ddI is unstable in an acidic environment. While the pH was found to be lower in the duodenum and proximal jejunum (approximately pH 6) than in the ileum or colon (pH > or = 7.0), ddI is reasonably stable across the entire pH range of the dog small intestine. These studies demonstrate that the regional reduction in ddI BA is consistent with a reported distal reduction in intestinal permeability and appears to be a significant contributing factor to the high degree of absorption variability reported for ddI.

Administration, Oral↗

PubMed2002

Minimal effect of ketoconazole on cyclosporine (SangCyA) oral absorption and first-pass metabolism in rats: evidence of a significant vehicle effect on SangCyA absorption.

The current work evaluated the effect of the CYP3A inhibitor ketoconazole on the oral absorption and first-pass metabolism of cyclosporine administered as the SangCyA formulation. Groups of 6 male Sprague-Dawley rats were administered SangCyA (5 and 15 mg/kg) by oral gavage alone and with ketoconazole (30 mg/kg). Blood cyclosporine levels were measured over 6 h, encompassing the cyclosporine absorption window. A significant vehicle effect on SangCyA absorption was observed. Comparing a 15 mg/kg dose, cyclosporine C(max) (mean+/-SD 1.12+/-0.16 microg/ml) and AUC(0-6) (5.34+/-0.71 microg h/ml) were 50% lower when propylene glycol was used as gavage vehicle instead of saline (2.19+/-0.94 microg/ml and 9.52+/-2.52 microg h/ml, respectively). Coefficients-of-variation for these parameters were halved in the propylene glycol vehicle however T(max) was unaffected. Ketoconazole increased cyclosporine C(max) and AUC(0-6) by 50-60%, regardless of the vehicle or the cyclosporine dose, without altering T(max) (2-3 h). The small effect of ketoconazole suggests that CYP3A-mediated intestinal and first-pass hepatic metabolism are minor determinants of cyclosporine oral bioavailability in rats.

Animals↗

PubMed2006

Intestinal absorption and presystemic disposition of sildenafil citrate in the rabbit: evidence for site-dependent absorptive clearance.

Sildenafil citrate is the first oral treatment for erectile dysfunction. Its oral bioavailability is about 40%. This research investigated the intestinal transport parameters of sildenafil citrate in rabbit using an in situ intestinal perfusion technique. This was studied in four different anatomical sites, namely duodenum, jejunoileum, ascending colon and rectum. The results revealed the highest absorptive clearance in the jejunoileum. The values of the permeability area product normalized to segment length (ml/min.cm) were 0.0101, 0.0063, 0.0059 and 0.0023 and those of the percentage absorbed were 68.0, 32.3, 23.0 and 5.0 in jejunoileum, duodenum, ascending colon and rectum, respectively. The values of the length (cm) required for complete absorption were 87.6, 137, 153 and 384 for each anatomical site in the same order. The absorptive clearance did not correlate with the net water flux in the four anatomical regions studied, indicating a mainly passive diffusion mechanism through a transcellular pathway. The plasma sildenafil concentrations achieved during intestinal perfusion experiments and sildenafil total body clearance in the rabbit were used to calculate the fraction of sildenafil that reached the systemic circulation relative to the amount that disappeared from the intestinal segment. Only 34% of sildenafil that disappeared from the intestinal segment appeared in the systemic circulation indicating that the presystemic elimination of sildenafil is 66%. These results confirm that the incomplete bioavailability of sildenafil is mainly due presystemic elimination.

Animals↗