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Biomedical subjects

R Hori

Publications and source records attributed to R Hori.

At least 19 recordsLinked to original sources
PubMed1992

Human P-glycoprotein transports cortisol, aldosterone, and dexamethasone, but not progesterone.

We expressed human MDR1 cDNA isolated from the human adrenal gland in porcine LLC-PK1 cells. A highly polarized epithelium formed by LLC-GA5-COL300 cells that expressed human P-glycoprotein specifically on the apical surface showed a multidrug-resistant phenotype and had 8.3-, 3.4-, and 6.5-fold higher net basal to apical transport of 3H-labeled cortisol, aldosterone, and dexamethasone, respectively, compared with host cells. But progesterone was not transported, although it inhibited azidopine photoaffinity labeling of human P-glycoprotein and increased the sensitivity of multidrug-resistant cells to vinblastine. An excess of progesterone inhibited the transepithelial transport of cortisol by P-glycoprotein. These results suggest that cortisol and aldosterone are physiological substrates for P-glycoprotein in the human adrenal cortex and that substances that efficiently bind to P-glycoprotein are not necessarily transported by P-glycoprotein.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1992

Transport of procainamide in a kidney epithelial cell line LLC-PK1.

Transport of procainamide, an anti-arrhythmic drug, was investigated in LLC-PK1 kidney epithelial cell line. The uptake of procainamide by LLC-PK1 monolayers cultured in plastic dishes was temperature-dependent, saturable and inhibited by organic cations such as cimetidine and N-acetylprocainamide. An aminocephalosporin antibiotic, cephalexin, also inhibited procainamide uptake, but an organic anion, p-aminohippurate, did not. The uptake of procainamide was greater at an alkaline external pH than at an acidic pH. In addition, procainamide uptake increased when intracellular pH was decreased and the uptake decreased when the intracellular pH was increased by ammonium chloride treatment, indicating the involvement of an H+/procainamide antiport system in apical membrane. The basolateral to apical flux of procainamide across LLC-PK1 monolayers cultured on permeable supports was 2.5-times larger than the apical to basolateral flux, and only the former process was inhibited by other organic cations. These findings suggest that LLC-PK1 cells can transport procainamide by the organic cation transport system and that procainamide is transported unidirectionally from basolateral to apical side across the cell monolayers.

Animals↗
PubMed1992

Expression of renal organic cation transporter in Xenopus laevis oocytes.

The expression of the organic cation transport system of rat renal proximal tubules has been studied in Xenopus laevis oocytes injected with poly(A)+ RNA from the rat renal cortex. The effectiveness of the technique was confirmed by examining expression of the Na+/D-glucose co-transporter. Compared with water-injected and non-injected oocytes, the injection of total poly(A)+ RNA resulted in about a 3-fold increase in tetraethylammonium (TEA) uptake activity. TEA uptake by poly(A)(+)-RNA-injected oocytes was time-dependent and was inhibited by cimetidine and HgCl2, but not by p-aminohippurate. After size-fractionation on a sucrose density gradient, a 1.4-2.4 kb poly(A)+ RNA fragment was identified that expressed the organic cation transport system in oocytes. These results demonstrate that the renal organic cation transporter was expressed in oocytes and that this expression system can provide an effective assay procedure for cloning of the organic cation transporter.

Animals↗
PubMed1992

A comparative study on immunosuppressive effects of cyclosporin A and FK 506 on peripheral blood lymphocytes in dogs.

Immunosuppressive effects of cyclosporin A (CsA) and FK 506 (FK) on peripheral blood lymphocytes were studied in dogs in respect to mixed lymphocyte reaction, proliferative responses to recombinant interleukin-2 (rIL-2), phytohemagglutinin (PHA) and concanavalin-A (Con-A); phenotypes of OKIa1, CD3, CD8 and surface IgM; cytotoxic activity against xenogeneic tumor cells. CsA (2.0 or 5.0 mg/kg, intravenously) or FK (0.16 mg/kg, intramuscularly) was given to mongrel dogs every morning for serial 21 days. The blood concentrations of CsA, measured as trough levels by fluorescence polarization method, ranged from 37 to 350 ng/ml in dogs administered at 2.0 mg/kg and from 170 to 894 ng/ml in dogs administered at 5.0 mg/kg during treatment, respectively. In dogs treated with FK at a dose of 0.16 mg/kg, the drug concentrations in the plasma during treatment ranged from 0.16 to 1.8 ng/ml. Mixed lymphocyte reaction and proliferative responses to rIL-2, PHA and Con-A, which were declined by CsA, were not affected by FK. In contrast, the proportion of OKIa1+ cells was not affected by CsA, whereas FK decreased the proportion of OKIa1+ cells progressively during the course of treatment. Cytotoxic activity was suppressed by both CsA and FK. These results possibly indicate that CsA and FK exert their immunosuppressive effects via different mechanisms.

Animals↗
PubMed1992

Transcellular transport of organic cation across monolayers of kidney epithelial cell line LLC-PK.

Transcellular transport and the accumulation of [14C]tetraethylammonium, a typical organic cation, by LLC-PK1 cell monolayers grown on microporous membrane filters were studied. Tetraethylammonium was accumulated progressively in the monolayers from the basolateral side and was transported unidirectionally to the apical side. The transcellular transport of tetraethylammonium was saturable, temperature dependent, and sensitive to the pH of the apical side of the monolayers. The apparent Michaelis constant and maximum velocity values for the transport were 67 microM and 222 pmol.mg protein-1.min-1, respectively. Unlabeled tetraethylammonium, amiloride, procainamide, cimetidine, and choline inhibited the basolateral uptake and transcellular transport of [14C]tetraethylammonium. The development of tetraethylammonium transport activity was observed in the differentiating cells. A sulfhydryl reagent inhibited the tetraethylammonium transport at both the basolateral and apical membranes of the LLC-PK1 cells. These findings suggest that these monolayers possess unidirectional transport systems for organic cations, corresponding to the secretion in the renal proximal tubules.

4-Chloromercuribenzenesulfonate↗
PubMed1992

Effect of leukotriene C4 on theophylline disposition in guinea pigs.

The pharmacokinetics of theophylline in acutely ill patients show wide intraindividual variability associated with the severity of clinical status. To investigate the mechanism of this variability, we studied the effects of leukotriene C4 (LTC4)-induced pathophysiologic changes on the disposition of theophylline. The plasma concentration-time profiles were measured after simultaneous intravenous bolus injection of theophylline and antipyrine in guinea pigs. The animals received 5 micrograms/kg of LTC4 intravenously 60 min later. The plasma theophylline concentration 30 min after LTC4 treatment was significantly lower (p less than 0.05) than that of nontreated control animals, whereas the plasma antipyrine concentration at that time was not affected. In addition, the treated animals showed significantly slower declines in plasma concentrations of both drugs (0.0805 +/- 0.0199 and 0.291 +/- 0.020 h-1 for theophylline and antipyrine, respectively, mean +/- SEM) than did controls (0.197 +/- 0.010 and 0.439 +/- 0.028 h-1). Leukotriene C4 treatment also induced moderate bronchoconstriction and metabolic acidosis, increased blood hemoglobin concentration and hematocrit, and decreased concentration of serum proteins. In connection with these changes, the plasma unbound fraction of theophylline increased significantly (p less than 0.001, 94.4 +/- 3.3% in treatment versus 58.2 +/- 4.4% in control), but that of antipyrine was unchanged (94.9 +/- 3.0% in treatment versus 92.1 +/- 0.9% in control). These findings indicated that an increase in the volume of distribution was responsible for the abrupt change in plasma theophylline concentration following LTC4 treatment, and the apparent change in the volume of distribution was estimated as 26.1 +/- 5.6%.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminophylline↗
PubMed1992

Direct modulation of secretin binding sites by gastrin in the rat stomach.

The effect of gastrin on secretin binding sites in the stomach was studied using the plasma membranes from rat gastric mucosa and vascularly perfused rat stomach. Tetragastrin transiently increased secretin binding to the mucosal plasma membranes. In the perfused stomach secretin binding was also modulated by the inclusion of tetragastrin or human [Leu15] gastrin I in the perfusate. However, histamine did not show such a modulatory effect. Tetragastrin had an insignificant effect on secretin binding sites in rat pancreas. These results suggest that the direct modulation of secretin binding by gastrin to its receptors may be involved in the inhibitory action of secretin on acid secretion induced by gastrin.

Animals↗
PubMed1992

Pharmacokinetics of brain natriuretic peptide in rats.

The pharmacokinetics of rat brain natriuretic peptide (rBNP) was compared with that of alpha-rat atrial natriuretic peptide (alpha-rANP) in rats. After intravenous infusion in rats (600 pmol min-1kg-1 for 2 min), the disappearance of plasma rBNP was 4-fold slower than that of alpha-rANP. The estimated mean plasma clearance rates for rBNP and alpha-rANP were 45.9 ml min-1kg-1 and 74.4 ml min-1kg-1, respectively. The affinity of rBNP for the clearance receptor or degradation enzyme was considered to be lower than that of alpha-rANP.

Animals↗
PubMed1992

Mechanisms of pharmacokinetic interaction between propranolol and quinidine in rats.

In order to study the mechanism of propranolol-quinidine interaction, the effects of quinidine on propranolol pharmacokinetics were examined in male Wistar rats. The concurrent oral administration of quinidine (10 mg/kg) markedly increased the plasma concentration of propranolol (2.5 mg/kg), and the area under the propranolol concentration-time curve increased about 3.6-fold. These results are consistent with previous observations in man and indicate the possible usefulness of the male Wistar rat as an animal model for investigating the mechanisms of the drug interaction. When propranolol was given intravenously, a concurrent administration of quinidine increased the apparent distribution volume of propranolol, mainly by decreasing its plasma protein binding. However, the systemic clearance of propranolol was not significantly altered by quinidine. Thus, quinidine increased the availability of oral propranolol from 13.8 +/- 2.2 to 44.2 +/- 4.6% (p less than 0.01). Furthermore, quinidine delayed the elimination of propranolol from the isolated perfused rat liver. These results indicate that quinidine reduces the presystemic elimination of propranolol in the liver, thereby increasing its systemic availability after oral administration.

Animals↗
PubMed1992

Mannan-coated liposome delivery of gadolinium-diethylenetriaminepentaacetic acid, a contrast agent for use in magnetic resonance imaging.

Gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA), a paramagnetic contrast agent for use in magnetic resonance imaging (MRI) was bound to stearylamine and incorporated into the liposomal membranes (Gd-DTPA liposomes). In addition, the Gd-DTPA liposomes were coated with mannan (cholesterol-aminoethylcarbamylmethyl mannan), a polysaccharide, to obtain the mannan-coated liposomes. An in vitro MRI study showed that the Gd-DTPA liposomes produced a greater intensity of contrast than did the Gd-DTPA solution with a reduced T1 relaxation time. Intravenous injection of the Gd-DTPA liposomes containing 153Gd or liposomes containing 153Gd or 14C-DTPA to mice showed an accumulation of Gd-DTPA primarily in the liver and lung. When the mannan-coated liposomes were administered, an increased uptake of Gd-DTPA by these tissues was demonstrated. The mannan-coated liposomes may enhance contrast of the liver in MRI at a lower dose of Gd-DTPA.

Animals↗
PubMed1992

Inhibition of apical membrane enzyme activities and protein synthesis by gentamicin in a kidney epithelial cell line LLC-PK1.

The mechanism of a gentamicin-induced decrease in apical membrane enzyme activities was investigated in LLC-PK1 cells. Increasing activities of apical membrane enzymes (alkaline phosphatase, aminopeptidase, and gamma-glutamyltransferase) were markedly suppressed by gentamicin during growth in culture. On the other hand, a lesser effect was observed when the activities of these enzymes were decreasing or relatively constant. Gentamicin treatment decreased the maximal enzyme activities of alkaline phosphatase and aminopeptidase, indicating that the number of active enzyme molecules in the apical membrane was decreased by gentamicin. [3H]Leucine incorporation in LLC-PK1 cells was inhibited by gentamicin in a dose-dependent manner, followed by a reduction of total protein. In addition, a well-known protein synthesis inhibitor, cycloheximide, also decreased the apical enzyme activities. These results suggest that the inhibition of protein synthesis by gentamicin is a possible cause of the decreased activities of apical membrane enzymes in LLC-PK1 cells. The inhibition of protein synthesis may be related to the nephrotoxicity induced by aminoglycoside antibiotics.

Animals↗
PubMed1992

Transport of digoxin by human P-glycoprotein expressed in a porcine kidney epithelial cell line (LLC-PK1).

This article represents the first evidence that the renal secretion of the commonly used drug, digoxin, is mediated by P-glycoprotein. In this study, it was demonstrated that digoxin is a substrate of P-glycoprotein, and the mechanism of a clinically important drug interaction, such as digoxin-quinidine, was elucidated. Human P-glycoprotein was expressed on the apical membrane of the porcine kidney epithelial cell line, LLC-PK1 by transfecting with human MDR1 cDNA. The expression and function of P-glycoprotein were confirmed by Southern and Western blotting, RNase protection assay, immunostaining and transporting activity for vinblastine. The transepithelial transport of [3H]digoxin was measured across the cell monolayers grown on microporous polycarbonate membrane filters. The transfectant cells exhibited markedly greater basal-to-apical transport and less apical-to-basal transport than the host cells, and the former was 8-fold greater than the latter. The augmented transepithelial transport resulted from the increased efflux from cells to apical side. This oriented transport was inhibited by the presence of 20 microM vinblastine, quinidine or verapamil. The rate of efflux to the apical side was 2-fold greater than that to the basal side. Quinidine inhibited the efflux to the apical side but did not affect transport into the basal side. These findings demonstrate that digoxin is transported by human P-glycoprotein, which is a previously undiscovered drug transport system in the kidney other than organic cation and anion transport systems, and suggest a molecular mechanism for the renal tubular secretion of digoxin as well as clinically important digoxin-quinidine interaction via P-glycoprotein.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1992

Surface binding and intracellular uptake of gentamicin in the cultured kidney epithelial cell line (LLC-PK1).

Aminoglycoside antibiotics such as gentamicin are taken up by renal proximal tubular cells, yet little is known regarding the biochemical characteristics of the transport process at the cellular level. In this report, cellular handling of gentamicin was studied in the cultured kidney epithelial cell line LLC-PK1. After 2 days of incubation of the cells with gentamicin, cell-associated gentamicin decreased rapidly during the first 30 min when the cells were incubated in gentamicin-free medium, then decreased slowly. The apparent half-life of the latter phase, which should represent release from the intracellular compartment, was about 2.0 days. The rapid release of gentamicin should consist of two components, one is a release from the cell surface membrane and the other from domes. Cell surface binding of gentamicin was dependent on the ambient ionic strength. The intracellular uptake was inhibited by low temperature, neomycin, metabolic inhibitors and reagents which interact with the cytoskeleton. On the other hand, the uptake was not affected by d-glucose, organic cations and an organic anion. Thus, by estimating the intracellular gentamicin separately from the drug localized in other compartments, it is concluded that gentamicin is taken up by LLC-PK1 cells via an adsorptive endocytosis. The endocytosis of gentamicin should be dependent on metabolic energy and cytoskeletal function.

Animals↗
PubMed1992

H+ coupled active transport of bestatin via the dipeptide transport system in rabbit intestinal brush-border membranes.

Bestatin [(2S,3R)-3-amino-2-hydroxy-4-phenylbutanoyl-L-leucine], a dipeptide containing an unusual amino acid, has been used clinically as an anticancer agent in p.o. dosage form. We examined the transport characteristics of [3H]bestatin by rabbit intestinal brush-border membrane vesicles. Bestatin uptake was stimulated by an inward H+ gradient (overshoot phenomenon) and by an interior-negative membrane potential. About half of the apparent bestatin uptake at 1 mM by brush-border membrane vesicles was estimated as binding to the membranes. The affinity constant for the bestatin transport was 0.52 mM. The uptake of bestatin by brush-border membrane vesicles was inhibited by p.o. cephalosporins and dipeptides, but not by amino acids. In vesicles preloaded with either bestatin, cephradine or glycylsarcosine, the uptake of [3H]bestatin was stimulated markedly (countertransport effect). These results indicate that bestatin is transported via the H+/dipeptide transport system in rabbit intestinal brush-border membranes.

Aminopeptidases↗
PubMed1991

Moment analysis of drug disposition in kidney. V: In vivo transepithelial transport of p-aminohippurate in rat kidney.

A new method that can assess the kinetics of in vivo transepithelial transport in rat kidney has been established. The method is based upon a multiple-indicator dilution experiment and the moment analysis theory. After simultaneous bolus injections of p-aminohippurate (PAH) and inulin into the right renal artery, blood samples were taken from the carotid artery and urine was separately collected from right and left ureters. The characteristic response for the first passage of drugs through the right kidney was evaluated by taking blood circulation into consideration. To determine the mean artery-to-vein transit time and the extraction ratio in the kidney, an intravenous injection was also performed as a reference experiment for deconvolution. The urinary excretion curve corresponding to the first passage was obtained as the difference between both kidneys. The mean artery-to-lumen transit time (mean transepithelial transit time, Tcell) was computed by subtracting the mean urinary transit time of inulin from that of secreted PAH. Since transport across the luminal membrane into the lumen from tubular epithelial cells can influence the cellular residence time of drugs, Tcell and the single-pass mean residence time in epithelial cells (Tcell,sp) can be thought of describing luminal membrane transport. The value of Tcell obtained for 0.1 mM PAH was 22 sec and it was prolonged to 61 sec in the presence of probenecid, suggesting an inhibitory effect on transport across the luminal membrane. On the other hand, antiluminal membrane transport into cells from blood is characterized by the volume of distribution in the kidney (VdPAH). VdPAH was remarkably decreased by treatment with probenecid, indicating an inhibitory effect on antiluminal membrane transport. The effects of probenecid on both sides of epithelial cell membrane transport were first demonstrated in vivo. The present method is useful for the analysis of in vivo transepithelial transport including antiluminal and luminal membrane transport for drugs excreted via tubular secretion.

Animals↗
PubMed1991

Moment analysis of drug disposition in kidney. VI: Assessment of in vivo transmembrane transport of p-aminohippurate in tubular epithelium.

This paper describes a novel method to assess the antiluminal membrane (ALM) and luminal membrane (LM) transport in vivo across renal tubular epithelial cells. The method is based upon a noncompartmental moment analysis of the plasma concentration and urinary excretion rate curves following renal artery injection. Quantitative relationships are represented between the noncompartmental parameters (clearance, volume of distribution, and the mean transit time) and the first-order rate constants associated with transmembrane transport processes. The in vivo transepithelial transport of [14C]p-aminohippurate (PAH) was examined using the rat kidney in the absence or presence of various plasma concentrations of unlabeled PAH, cefazolin, and methotrexate. The tubular secretion intrinsic clearance was reduced with an increase in the plasma concentration of concurrent unlabeled organic anions. The distribution volume of PAH in the kidney decreased in association with a decrease in the amount of PAH secreted, whereas the mean transepithelial (artery-to-lumen) transit time (Tcell) remained constant. These findings indicate that ALM transport is a capacity-limited process determining the amount of tubular secretion, and that LM transport is linear over the concentration range examined and independent of the amount of secretion. The contribution of ALM and LM transport to transcellular transport was first clarified in vivo. The present method will be useful for analyzing the transmembrane transport processes in vivo for highly diffusible substances in the kidney.

Animals↗
PubMed1991

Enhanced bioavailability of subcutaneously injected insulin by pretreatment with ointment containing protease inhibitors.

The present study was undertaken to develop an ointment preparation containing a protease inhibitor for stabilizing subcutaneously injected insulin. The ointment containing the protease inhibitor, gabexate mesilate or nafamostat mesilate, was applied to the skin around the insulin injection site. Three results were obtained. First, gabexate and nafamostat inhibited insulin degradation in subcutaneous tissue homogenates in vitro. Second, after application of gabexate or nafamostat ointment, an appreciable amount of gabexate or nafamostat appeared in the subcutaneous tissue of rats or hairless mice and their concentrations were comparable to those seen in the in vitro experiment. Third, insulin degradation at the subcutaneous injection site in the rat was depressed after pretreatment with gabexate or nafamostat ointment. Pretreatment with gabexate or nafamostat ointment increased the plasma immunoreactive insulin (IRI) levels and the hypoglycermic effect of insulin in healthy volunteers. These results indicate that gabexate or nafamostat ointments stabilize subcutaneously injected insulin.

Administration, Topical↗