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  • 1
    Electronic Resource
    Electronic Resource
    Peptide Transporter in the Rat Small Intestine: Ultrastructural Localization and the Effect of Starvation and Administration of Amino Acids (1999)
    Springer
    Journal of molecular histology 31 (1999), S. 169-174 
    Details
    ISSN: 1573-6865
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Peptide transporter-1 is a H+/peptide cotransporter responsible for the uptake of small peptides and peptide-like drugs, and is present in the absorptive epithelial cells of the villi in the small intestine (duodenum, jejunum, and ileum). It has been localized to the apical microvillous plasma membrane of the absorptive epithelial cells of the rat small intestine using the immunogold electron microscopic technique. Digital image analysis of the jejunum revealed that the transporter protein was abundant at the tip of the villus and that the amount decreased from the tip of the villus to its base. The effect of dietary administration of amino acids and starvation on the expression of PepT1 in the jejunum was examined by immunoblotting and image analysis of immunofluorescence. Starvation markedly increased the amount of peptide transporter present, whereas dietary administration of amino acids reduced it. The gradient of the transporter protein along the crypt-villus axis was maintained under either condition. These observations show that it is specific to the microvillous plasma membrane and that its expression is regulated by the nutritional condition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003515413550
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  • 2
    Electronic Resource
    Electronic Resource
    Simulation for population analysis of Michaelis-Menten elimination kinetics (1995)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 23 (1995), S. 205-216 
    Details
    ISSN: 1573-8744
    Keywords: Michaelis-Menten kinetics ; NONMEM ; population pharmacokinetics ; statistical simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A simulation study was conducted to compare the cost and performance of various models for population analysis of the steady state pharmacokinetic data arising from a one-compartment model with Michaelis-Menten elimination. The usual Michaelis-Menten model (MM) and its variants provide no estimate of the volume of distribution, and generally give poor estimates of the maximal elimination rate and the Michaelis-Menten constant. The exact solution to the Michaelis-Menten differential equation (TRUE) requires a precise analysis method designed for estimation of population pharmacokinetic parameters (the first-order conditional estimation method) and also considerable computational time to estimate population mean parameters accurately. The one-compartment model with dose-dependent clearance (DDCL), in conjunction with the first-order conditional estimation or Laplacian method, ran approximately 20-fold faster than TRUE and gave accurate population mean parameters for a drug having a long biological half-life relative to the dosing interval. These findings suggest that the well-known MM and its variants should be used carefully for the analysis of blood concentrations of a drug with Michaelis-Menten elimination kinetics, and that TRUE, in conjunction with a precise analysis method, should be considered for estimating population pharmacokinetic parameters. In addition, DDCL is a promising alternative to TRUE with respect to computation time, when the dosing interval is short relative to the biological half-life of a drug.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02354272
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of Intestinal and Hepatic Metabolism on the Bioavailability of Tacrolimus in Rats (1998)
    Springer
    Pharmaceutical research 15 (1998), S. 1609-1613 
    Details
    ISSN: 1573-904X
    Keywords: tacrolimus ; bioavailability ; metabolism ; intestine ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Tacrolimus, an immunosuppressive agent, has poor and variable bioavailability following oral administration in clinical use. We investigated the contribution of intestinal metabolism to the first pass effect of tacrolimus in rats. Methods. Tacrolimus was administered intravenously, intraportally or intraintestinally to rats. Blood samples were collected over a 240-min period, and blood tacrolimus concentrations were measured. The extraction ratios of tacrolimus in the intestine and liver were investigated. In addition, the metabolism of tacrolimus in the everted sacs of the small intestine was examined. Results. The rate of absorption of tacrolimus in the intestine was rapid, and tacrolimus was almost completely absorbed after intestinal administration. The bioavailability of tacrolimus was about 40% and 25% after intraportal and intraintestinal administration, respectively, indicating that tacrolimus is metabolized in both the intestine and the liver. In addition, tacrolimus was significantly metabolized in the everted sacs of the rat intestine. Conclusions. The present study suggested that the metabolism of tacrolimus in the intestine contributes to its extensive and variable first pass metabolism following the oral administration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011967519752
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  • 4
    Electronic Resource
    Electronic Resource
    Modulation of Organic Cation Transport and Lipid Fluidity by Benzyl Alcohol in Rat Renal Brush-border Membranes (1996)
    Springer
    Pharmaceutical research 13 (1996), S. 1069-1072 
    Details
    ISSN: 1573-904X
    Keywords: renal transport ; organic cation ; membrane fluidity ; brush-border membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Organic cations are actively transported in renal brush-border membranes (BBM) by the H+/organic cation antiport system. In the present study, we investigated the relationship between membrane fluidity and organic cation transport in the BBM. Methods. The effects of benzyl alcohol, a membrane fluidizing agent, on the organic cation tetraethylammonium (TEA) uptake were studied using renal BBM vesicles isolated from rat kidney. BBM fluidity was assessed by fluorescence polarization technique. Results. H+ gradient-dependent uptake of TEA in BBM vesicles was inhibited by benzyl alcohol in a dose-dependent manner, with an apparent half inhibitory concentration of 18mM. The decrease in fluorescence anisotropy of l,6-diphenyl-l,3,5-hexatriene in BBM, which represents the increase in membrane fluidity, was correlated with the decrease in TEA transport activity. The dissipation rate of H+ gradient, a driving force for organic cation transport in BBM, was increased by benzyl alcohol. In addition, H+ gradient-independent TEA-TEA exchange was also inhibited by benzyl alcohol. These findings indicate that benzyl alcohol inhibits the uptake of TEA by affecting the intrinsic activity of the organic cation transporter and the H+ gradient dissipation rate. Conclusions. The membrane fluidity should be an important determinant for organic cation transport in renal BBM.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016066926269
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of Cyclosporin Analogues and FK506 on Transcellular Transport of Daunorubicin and Vinblastine via P-glycoprotein (1996)
    Springer
    Pharmaceutical research 13 (1996), S. 1073-1077 
    Details
    ISSN: 1573-904X
    Keywords: P-glycoprotein ; cyclosporins ; FK506 ; daunorubicin ; vinblastine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. P-glycoprotein-mediated transcellular transport of anticancer agents and the inhibitory effect of cyclosporin analogs and FK506 were investigated. Methods. The transcellular transport of daunorubicin and vinblastine by monolayers of LLC-GA5-COL150 cells which overexpressed P-glycoprotein was measured in the presence and absence of cyclosporins or FK506. Results. Cyclosporins and FK506 inhibited P-glycoprotein-mediated transport of daunorubicin and vinblastine in the order of cyclosporin D, dihydrocyclosporin D 〉 cyclosporin A 〉 FK506 〉 cyclosporin C, dihydrocyclosporin C. The intracellular accumulation of the anticancer agents was highly associated with the transporting function of P-glycoprotein. The inhibitory effect of cyclosporin D was concentration-dependent. The inhibitory effect of the modulators on P-glycoprotein was not correlated with the immunosuppressive activity, but was correlated with their lipophilicity. Conclusions. In the transcellular transport system, lipophilicity may be one of the determinants for the inhibitory effect of various multidrug resistance modulators on the P-glycoprotein-mediated transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016019010339
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  • 6
    Electronic Resource
    Electronic Resource
    Transport Characteristics of Ceftibuten, a New Cephalosporin Antibiotic, via the Apical H+/Dipeptide Cotransport System in Human Intestinal Cell Line Caco-2: Regulation by Cell Growth (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 1483-1487 
    Details
    ISSN: 1573-904X
    Keywords: cephalosporin antibiotics ; H +/dipeptide cotransporter ; Caco-2 cells ; cell growth ; intestinal absorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The intestinal epithelial cell line Caco-2 possesses the H+/ dipeptide cotransport system responsible for uptake of oral cephalosporins. In this study, the transport characteristics of ceftibuten were examined from the viewpoint of cell growth in the Caco-2 cells. Methods. The uptake of cephalosporins by Caco-2 cell monolayers grown on plastic dishes was measured and analyzed kinetically. Results. The uptake of ceftibuten was increased by lowering pH of the incubation medium and was inhibited by excess dipeptide. The transport activity of ceftibuten was dependent on the duration of culture, being maximal on the 14th day after inoculation. Kinetic analysis revealed that the development of ceftibuten uptake was due to not only a decrease in Km but also to an increase in Vmax value. Conclusions. The uptake of ceftibuten is mediated by the apical H+/ dipeptide cotransport system which is regulated by cell growth and/or differentiation in the Caco-2 cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016235404598
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  • 7
    Electronic Resource
    Electronic Resource
    Evaluation of Renal Tubular Secretion and Reabsorption of Levofloxacin in Rats (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 508-511 
    Details
    ISSN: 1573-904X
    Keywords: levofloxacin ; quinolone antibacterial drugs ; renal secretion ; organic cation transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. Levofloxacin, a quinolone antibacterial drug, is a zwitterion at physiological pH. We examined the effect of cationic and anionic drugs on renal excretion of levofloxacin by means of in vivo clearance to characterize the mechanisms of renal excretion of this drug. Methods. In vivo clearance was studied in male Wistar albino rats. A bolus dose of 2.85 mg/kg of levofloxacin was administered, followed by a constant infusion of 7.08 μg/min. Cimetidine, tetraethylammonium, or p-aminohippurate was administered as a bolus and incorporated into the infusion solution. After reaching steady state, urine and blood concentrations were measured, and pharmacokinetic parameters were calculated. Results. Renal clearance was 2.56 ± 0.42 ml/min in control, which accounted for 34% of the total body clearance. Renal clearance was significantly decreased to 0.83 ± 0.25 ml/min by cimetidine (p〈.05), corresponding to 32% of the control value. The cationic drug, tetraethylammonium also reduced the renal clearance of levofloxacin, but the effect of the anionic drug, p-aminohippurate, was slight. The clearance ratio of levofloxacin, which was calculated by renal clearance divided by the plasma unbound fraction and the glomerular filtration rate, was 1.60 ± 0.38 in the control and it was decreased to 0.68 ± 0.17 and 1.11 ± 0.22 by cimetidine and tetraethylammonium, respectively. Conclusions. The present results suggest that the renal excretion of levofloxacin in rats involves tubular secretion and reabsorption, in addition to glomerular filtration, and that tubular secretion is inhibited by cimetidine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012111902798
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  • 8
    Electronic Resource
    Electronic Resource
    Distribution Characteristics of Levofloxacin and Grepafloxacin in Rat Kidney (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 534-539 
    Details
    ISSN: 1573-904X
    Keywords: levofloxacin ; grepafloxacin ; quinolone antibacterial drugs ; renal transport ; tissue distribution ; cortical slices
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. To elucidate the renal distribution of quinolones, we examined the uptake of levofloxacin and grepafloxacin in vivo and in rat renal cortical slices. Methods. The plasma and various tissue concentrations of levofloxacin and grepafloxacin were measured after a bolus injection in rats, and tissue uptake clearance was calculated. Transport characteristics of quinolones in rat renal cortical slices were evaluated. Results. The tissue distribution of levofloxacin and grepafloxacin in the kidney was greater than in any other tissue, and the tissue uptake clearances of levofloxacin and grepafloxacin in the kidney cortex were 1.2 and 4.6 ml/min/g tissue, respectively. The uptake of levofloxacin and grepafloxacin in rat renal cortical slices was concentrative, as indicated by slice/medium ratios of 2.3 and 9.6 at 60 min, respectively. The uptake of levofloxacin and grepafloxacin in rat renal cortical slices showed saturation, and was significantly inhibited in the presence of quinidine (p 〈 .05), but not of tetraethylammonium or /p-aminohippurate. Conclusions. Renal distribution of levofloxacin and grepafloxacin may be mediated by a specific transport system for quinolones, distinct from the organic cation and organic anion transport systems in the kidney.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018871029244
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  • 9
    Electronic Resource
    Electronic Resource
    Kinetic Analysis of Tetraethylammonium Transport in the Kidney Epithelial Cell Line, LLC-PK1 (1997)
    Springer
    Pharmaceutical research 14 (1997), S. 1236-1240 
    Details
    ISSN: 1573-904X
    Keywords: organic cation ; epithelial transport ; LLC-PK1 ; kinetic model ; levofloxacin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The aims of this study were to establish a kinetic means of analyzing the membrane transport of organic cations in renal epithelial cells, and to simultaneously evaluate drug interactions in apical and basolateral membranes. Methods. Tetraethylammonium (TEA) transport was measured using LLC-PK1, cell monolayers grown on microporous membrane filters. After incubating the cells with unlabeled TEA or other drugs, apical or basolateral medium was changed to that containing labeled TEA, and transcellular transport and cellular accumulation were measured. Clearance from apical medium to cells (CL12), cells to apical medium (CL21), cells to basolateral medium (CL23) and basolateral medium to cells (CL32) were calculated based on a three compartment model. Results. TEA was accumulated progressively in the monolayers from the basolateral side and was transported unidirectionally to the apical side. CL32 was greater than CL12 and CL23 was greater than CL21. Therefore, the rate limiting step of TEA transport from the basolateral to the apical medium was the cell-to-apical step. Co-incubation of TEA with procainamide decreased the transport parameters of TEA, CL12, CL21 and CL32, whereas that with levofloxacin decreased only CL12 and CL21, not affecting the parameters in basolateral membranes. Conclusions. Using a simple model, we analyzed the transport of organic cation in kidney epithelial cell line, LLC-PK1 This method can be useful for the analysis of cation transport and drug interactions in the apical and basolateral membranes of renal tubules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012119210434
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  • 10
    Electronic Resource
    Electronic Resource
    Effects of Arbekacin and Vancomycin on Release of Lactate Dehydrogenase and Fragmentation of DNA in LLC-PK1 Kidney Epithelial Cells (1999)
    Springer
    Pharmaceutical research 16 (1999), S. 1132-1135 
    Details
    ISSN: 1573-904X
    Keywords: arbekacin ; vancomycin ; cisplatin ; apoptosis ; toxicity ; LLC-PK1 cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011919306412
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