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PubMed1986

Is 3,4-dihydroxyphenylglycol the major route of central norepinephrine metabolism in rat brain?

Central norepinephrine (NE) metabolism was assessed by measuring 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) and 3,4-dihydroxyphenylethyleneglycol (DHPG) in different rat brain areas after saline or probenecid (300 mg/kg) administration. Under probenecid, results showed an increased accumulation of total MHPG and DHPG, and a clear preponderance of DHPG levels over MHPG in almost all the brain areas examined. Estimation of their formation rates confirmed that in basal conditions DHPG is formed more rapidly. This study supports the notion that, without ruling out the importance of MHPG, brain DHPG may be a useful index of central NE activity.

Animals↗
PubMed1989

Tryptophan, 5-HTP, 5-HT and 5-HIAA in the cerebrospinal fluid and sexual behavior in male rats.

No changes were found in the concentration of tryptophan (Trp), 5-hydroxytryptophan (5-HTP), 5-hydroxytryptamine (5-HT) or 5-hydroxyindole acetic acid (5-HIAA) in the cerebrospinal fluid (CSF) of male rats either before sexual activity, immediately after ejaculation of after the postejaculatory refractory period (PEI). Injection of the Trp hydroxylase inhibitor p-chlorophenylalanine (PCPA, 25 or 100 mg/kg i.p. for 3 days) in combination with an injection of the monoamine oxidase inhibitor pargyline (100 mg/kg i.p.) increased the concentration of Trp while decreasing the concentration of 5-HTP, 5-HT and 5-HIAA in the CSF. Furthermore 100 (but not 25) mg/kg PCPA in combination with pargyline caused a significant reduction in the latency to ejaculation. Injection of probenecid (200 mg/kg i.p.), an inhibitor of the transport of 5-HIAA from the CSF, increased the concentration of 5-HIAA in the CSF and slightly prolonged the latency to ejaculation. Sexual activity caused no further increase in CSF 5-HIAA levels in the probenecid-treated rats. Since drug-induced changes in sexual behavior are associated with marked alterations in 5-HT metabolism in the CSF, whereas the changes in the behavior which occur normally are not, these results question the physiological significance of the proposed inhibitory role of 5-HT in male rat sexual behavior.

5-Hydroxytryptophan↗
PubMed1995

Nephrotoxicity mechanism of 1,1-dichloroethylene in mice.

Male Swiss OF1 mice were administered orally with a single dose (200 mg/kg) of 1,1-dichloroethylene (DCE). Examination of cryostat kidney sections stained for alkaline phosphatase (APP) revealed damage to about 50% of the proximal tubules at 8 h following DCE administration. Pretreatment with the anionic transport inhibitor probenecid by i.p., (0.75 mmol/kg, 30 min prior to and 10 min and 5 h following DCE administration) and with the gamma-glutamyltranspeptidase (GGT) inactivator acivicin by gavage and i.p. (50 mg/kg, 1 h and 30 min prior to DCE administration) failed to prevent DCE-induced renal toxicity. Pretreatment with the beta-lyase inactivator amino-oxyacetic acid (AOAA) by gavage (100 mg/kg, 30 min prior to and 10 min and 5 h following DCE administration), and with the renal cysteine conjugate S-oxidase inhibitor methimazole by i.p. (40 mg/kg, 30 min prior to DCE administration) reduced the number of damaged tubules by approximately 50 and 60%, respectively in mice treated with DCE. The results suggest that the DCE undergoes biotransformation by NADPH-cytochrome P450 to several reactive species which conjugate with glutathione (GSH). After arriving in the kidneys, the resulting conjugates reach the renal cells by a mechanism which depends on neither GGT, nor on an anionic transport system which is sensitive to probenecid. Once in the cells, the presumed GSH conjugates and/or their derivatives undergo secondary modification by beta-lyase and cysteine conjugate S-oxidase to reactive metabolite(s).

Activins↗
PubMed1994

Nephrotoxicity mechanism of cis-platinum (II) diamine dichloride in mice.

Male Swiss OF1 mice were injected subcutaneously with 20 mg/kg of cis-platinum (II) diamine dichloride (cis-platin). Examination of cryostat kidney sections stained for alkaline phosphatase (APP) revealed damage to about 10, 20, 40 and 50% of the proximal tubules after 7, 24, 48 and 72 h, respectively. Pretreatment with the glutathione synthesis inhibitor, buthionine sulfoximine (BSO), (i.p. 3 mmol/kg) potentiated the tubule damage of cis-platin. In contrast, pretreatment with organic anion transport inhibitor probenecid (i.p. 3 x 0.75 mmol/kg) reduced the number of damaged tubules by approximately 80% at 72 h after cis-platin injection. Pretreatment with the gamma-glutamyltranspeptidase (gamma-GT) inactivator acivicin (AT-125, 50 mg/kg p.o., plus 50 mg/kg i.p.) failed to prevent cis-platin induced renal toxicity. Pretreatment with the beta-lyase inactivator aminooxyacetic acid (AOAA, 2 x 100 mg/kg p.o.) and with the renal cysteine conjugate S-oxidase inhibitor methimazole (40 mg/kg i.p.) reduced the number of damaged tubules by approximately 40% and 75%, respectively in mice treated with cis-platin. The results suggest that the platinum-sulfhydryl group complexes formed are taken up by the kidney cells through an organic anion transport mechanism which is probenecid-sensitive. In the cells these complexes are stable for several hours, depending on the intracellular glutathione (GSH) level, and gradually undergo transformation to reactive metabolite(s) by renal intracellular beta-lyase and S-oxidase.

Alkaline Phosphatase↗
PubMed1993

Improved detection limits for screening of diuretics by coupled liquid chromatography and ultraviolet-visible spectrophotometry.

Experimental conditions have been studied in order to improve the sensitivity for the analysis of diuretics and probenecid in urine samples by high-performance liquid chromatography with ultraviolet detection. Sample clean-up and chromatographic parameters have been optimized to obtain a suitable sensitivity for the detection or quantification of each diuretic using an HP-Hypersil ODS-C18 column (5 microns, 250 mm x 4 mm I.D.), taking into account the pharmacological properties of each compound. The reliability of this method was tested by analysing urine samples after a minimum single-dose administration of chlorthalidone and probenecid.

Chlorthalidone↗
PubMed2005

Systemically administered glucosamine-kynurenic acid, but not pure kynurenic acid, is effective in decreasing the evoked activity in area CA1 of the rat hippocampus.

The metabolism of tryptophan along the kynurenine pathway yields several neuroactive intermediates, including kynurenic acid, which is one of the few known endogenous N-methyl-d-aspartate receptor inhibitors; in parallel with this, it is an alpha7 nicotinic acetylcholinergic receptor antagonist. On the basis of these properties, kynurenic acid might therefore come into consideration as a therapeutic agent in certain neurobiological disorders. However, the use of kynurenic acid as a neuroprotective agent is practically excluded because kynurenic acid hardly crosses the blood-brain barrier. We recently synthetized a new compound, glucosamine-kynurenic acid, which is presumed to cross the blood-brain barrier more easily. In this study, the effects of systemically administered kynurenic acid and glucosamine-kynurenic acid on CA3 stimulation-evoked population spike activity in region CA1 of the rat hippocampus were compared. The effect of kynurenic acid or glucosamine-kynurenic acid was augmented by probenecid (200 mg/kg), which inhibits kynurenic acid excretion from the cerebrospinal fluid. The results showed that, while kynurenic acid administered i.p. or i.v. in doses of 17, 34, 68 or 136 micromol/kg did not cause any observable change in the animals, 136 micromol/kg glucosamine-kynurenic acid (either i.p. or i.v.) resulted in the sudden death of all the animals. The dose of 68 micromol/kg i.v., but not i.p., resulted in a sudden stoppage of breath, but the animals could be reanimated. As small a dose of glucosamine-kynurenic acid as 17 micromol/kg i.p. resulted in a reduction in population spike amplitudes; this effect was further augmented by probenecid, whereas neither 17 micromol/kg nor higher doses of pure kynurenic acid had a similar effect. The results presented here suggest that glucosamine-kynurenic acid passes the blood-brain barrier much more readily than does kynurenic acid.

Action Potentials↗
PubMed2006

Function of multidrug resistance-associated protein 2 in acute hepatic failure rats.

The function of multidrug resistance-associated protein 2 (Mrp2) in the intestine and liver, as well as intestinal Mrp2 expression, was analyzed in CCl(4)-induced acute hepatic failure rats with hyperbilirubinemia. The plasma level of bilirubin glucuronides, endogenous Mrp2-substrates, was 26 microM at 24 h after CCl(4) treatment. Mrp2 protein levels in jejunum decreased to 41% of control level. Mrp2-mediated efflux of 2,4-dinitrophenyl-S-glutathione (DNP-GSH), an Mrp2-substrate, in jejunum decreased to 31% of control in vitro, and was almost completely suppressed in vivo to the same level as that in the presence of probenecid, an Mrp2-inhibitor. Biliary excretion of DNP-GSH was suppressed to the same level as that inhibited by intravenous probenecid. The suppression of Mrp2 and the increased plasma bilirubin glucuronides recovered within 24 h thereafter. These results suggest that hyperbilirubinemia in disease states may be related to the systemic suppression of Mrp2 function.

ATP-Binding Cassette Transporters↗
PubMed2006

Evidence of Oatp and Mdr1 in cryopreserved rat hepatocytes.

Transport proteins control uptake of drugs into the liver (e.g., organic anion transporting polypeptide (Oatp)) and excretion of drugs from the liver (e.g., multidrug resistance protein 1 (Mdr1)). In this study, cryopreserved rat hepatocytes were used to investigate the effect of different culture conditions (suspension, conventional culture and sandwich culture) on the uptake of [(3)H]-taurocholate+/-probenecid and the efflux of [(3)H]-vinblastine+/-ketoconazole; mRNA levels of Oatp1a1, Oatp1a4, Mdr1a and Mdr1b were determined using real-time reverse transcription polymerase chain reaction (RT-PCR) and protein expression of Mdr was assessed by immunocytochemistry. The uptake of [(3)H]-taurocholate was higher in cryopreserved rat hepatocytes maintained in suspension as compared to hepatocytes in culture. A significant time dependent decline in the uptake of [(3)H]-taurocholate was noticed from day 2 to day 4 in conventional and sandwich cultures. [(3)H]-taurocholate uptake was significantly reduced using the inhibitor probenecid. Oatp mRNA expression in hepatocytes in suspension was similar to that of liver, whereas much lower levels were detected in the cultures; this was in accordance with [(3)H]-taurocholate uptake results. Mdr1 activity was assessed by accumulation of the Mdr1 selective substrate, [(3)H]-vinblastine, in hepatocytes using ketoconazole as an inhibitor. The results showed Mdr1 activity in cryopreserved rat hepatocytes in conventional and sandwich cultures. A time dependent increase in Mdr1 activity was noticed from day 2 to day 4. Mdr1 activity was not found using hepatocytes in suspension. Mdr1 mRNA expression was high in cryopreserved hepatocytes from both culture systems. Immunocytochemistry showed the Mdr protein in membranes of hepatocytes in culture as well as in that of hepatocytes in liver sections. In conclusion, the present study showed that cryopreserved rat hepatocytes maintained canalicular transport activity (Mdr1) and basolateral transport activity. Hepatocytes in suspension had a higher uptake of taurocholate with a high Oatp (1a1 and 1a4) mRNA expression as compared to hepatocytes in culture. The presence of Mdr1 in both conventional and sandwich culture was confirmed at mRNA level, by protein expression as well as transport activity.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed2000

Ocular side-effects from systemic HPMPC (Cidofovir) for a non-ocular cytomegalovirus infection.

PURPOSE: To report a case of anterior uveitis and ocular hypotony during HPMPC treatment of a cytomegalovirus infection without ophthalmic involvement. METHODS: A 61-year-old bisexual white man with AIDS presented with moderate anterior uveitis and ocular hypotony after 8 weeks of intravenous HPMPC and oral probenecid co-treatment of a presumed recurrence of cytomegalovirus encephalitis. RESULTS: There was no evidence of an ocular cytomegalovirus infection. Cidofovir-related uveitis was diagnosed, and the HPMPC-probenecid co-treatment was switched to ganciclovir monotherapy. The ocular inflammation was successfully managed with topical steroids and mydriatics. CONCLUSIONS: This description of ophthalmic side effects from systemic HPMPC in the absence of ocular cytomegalovirus infection supports the hypothesis that anterior uveitis and ocular hypotony result from a direct interaction between the drug and the ciliary body.

AIDS-Related Opportunistic Infections↗
PubMed2001

Characterization of organic anion transport inhibitors using cells stably expressing human organic anion transporters.

The organic anion transport system is involved in the tubular excretion of various clinically important drugs. The purpose of this study was to characterize the effects of various organic anion transport inhibitors on organic anion transport using proximal tubule cells stably expressing human organic anion transporter 1 (human-OAT1) and human-OAT3, which are localized to the basolateral membrane of the proximal tubule. Organic anion transport inhibitors including betamipron, cilastatin, KW-3902 (8-(noradamantan-3-yl)-1,3-dipropylxanthine) and probenecid significantly inhibited human-OAT1- and human-OAT3-mediated organic anion uptake in a dose-dependent manner. Kinetic analyses revealed that these inhibitions were competitive. The Ki values of betamipron, cilastatin, KW-3902 and probencid for human-OAT1 were 23.6, 1470, 7.82 and 12.1 microM, whereas those for human-OAT3 were 48.3, 231, 3.70 and 9.0 microM. These results suggest that betamipron and probenecid could inhibit both human-OAT1- and human-OAT3-mediated organic anion transport in vivo, whereas cilastatin could inhibit only human-OAT3-mediated one. In contrast, KW-3902 did not exert the effects of significance, whereas KW-3902 was the most potent.

Alanine↗
PubMed1998

Functional characterization of the rat multispecific organic anion transporter OAT1 mediating basolateral uptake of anionic drugs in the kidney.

The functional characteristics of rat organic anion transporter OAT1 were investigated using Xenopus laevis oocytes. Uptake of p-aminohippurate (PAH) by the oocytes expressing OAT1 was markedly inhibited by glutarate, alpha-ketoglutarate and probenecid, moderately inhibited by folate and methotrexate, but not inhibited by taurocholate or tetraethylammonium. Methotrexate and folate were transported by OAT1, but probenecid, a typical inhibitor of organic anion transporter, was not transported. Inhibition of PAH uptake by aliphatic dicarboxylates with various alkyl chain lengths was maximal at 5 (glutarate) and 6 (adipate) carbon atoms. OAT1-mediated PAH uptake was markedly inhibited by phorbol 12-myristate 13-acetate (PMA), phorbol 12,13-dibutyrate and mezerein, but not by 4alpha-phorbol 12,13-didecanoate. The inhibitory effect of PMA was attenuated in the presence of staurosporine, suggesting that OAT1 is regulated by protein kinase C. These results suggest that the substrate recognition of OAT1 is comparable to that of renal basolateral organic anion transporter, and the transport activity is regulated by protein kinase C.

Animals↗
PubMed1997

Calcein is excreted from the intestinal mucosal cell membrane by the active transport system.

In this study, we report the efflux mechanism of calcein, an organic anion, mediated by a multidrug resistance-associated protein (MRP)-like protein in the intestinal mucosal membrane. The transport of calcein from the mucosal to serosal side was decreased dose-dependently and was significantly lower than that of the opposite direction. In addition, its transport was increased in the presence of metabolic inhibitors and probenecid. Furthermore, the efflux of calcein from the intestinal cell membrane, which was preloaded with calcein acetoxymethyl ester, was predominantly observed in the mucosal side rather than in the serosal side. Its efflux to the mucosal side was inhibited by the metabolic inhibitors and probenecid, not by verapamil which is a P-glycoprotein substrate. These results indicated that the transport of calcein and possibly other organic anions across the intestinal membrane may be regulated by the MRP-like protein, but not P-glycoprotein.

Animals↗
PubMed2000

Brain distribution of 6-mercaptopurine is regulated by the efflux transport system in the blood-brain barrier.

6-mercaptopurine (6-MP) has been used clinically for 40 years to maintain remission in patients with acute lymphoblastic leukemia (ALL). However, central nervous system (CNS) relapses frequently occur in patients with ALL who continuously receive anticancer drugs, including 6-MP, during remission maintenance therapy. The cause of such CNS relapse is not well understood. One possible reason may involve the restricted distribution of 6-MP in the brain. This study, therefore, investigates the blood-brain barrier (BBB) transport which largely regulates 6-MP distribution in the brain using a quantitative microdialysis technique and centers on the efflux transport of 6-MP across the BBB. The brain tissue, cerebrospinal fluid (CSF), or hippocampal interstitial fluid (ISF) concentration of 6-MP was very low compared with the unbound plasma concentration, suggesting that 6-MP distribution in the brain is highly restricted. Kinetic analyses of this BBB transport showed that the efflux clearance from brain ISF to plasma across the BBB (CLout) is approximately 20-times greater than the influx clearance from plasma to brain (CLin). The CLout was significantly reduced by 1mM N-ethylmaleimide (NEM), a sulfhydryl-modifying agent, suggesting the participation of transport protein in the efflux of 6-MP across the BBB. In addition, efflux transport was inhibited by an intracerebral infusion of probenecid (1.5 mM), p-aminohippuric acid (PAH, 3.0 mM), benzoate (3.6 mM), or salicylate (3.7 mM) administered through a microdialysis probe, but neither choline (0.8 mM) nor tetraethylammonium (TEA, 0.7 mM) had any effect. These data suggest that the restricted 6-MP brain distribution may be ascribed to efficient efflux from the brain, possibly via both the organic anion transport system, shared with probenecid and PAH, and the monocarboxylic acid transport system, shared with benzoate and salicylate.

Animals↗
PubMed1997

Prostaglandin uptake and catabolism by the choroid plexus during development in sheep.

We have previously reported that prostaglandin(PG) E2 levels in sheep cerebrospinal fluid (CSF) are high prenatally and abate rapidly after birth. This event may contribute to the establishment of continuous breathing. To explain this change, we have examined PG disposal mechanisms in the perinatal and adult (pregnant and non-pregnant animal) sheep brain by measuring the capacity of the isolated choroid plexus to concentrate [3H]PGF2alpha and [3H]PGE2. At 0.9 gestation, [3H]PGF2alpha uptake (expressed as the tissue-to-medium ratio, T/M) attained a steady-state by 15 min and was maintained thereafter (T/M at 60 min, 5.6 +/- 0.6; n = 16). Likewise, [3H]PGE2 was taken up by the tissue, but the actual accumulation was smaller (T/M at 60 min, 2.6 +/- 0.2; n = 8). Thin-layer radiochromatographic analysis of the tissue following incubation with [3H]PGF2alpha showed that 55 +/- 4% (n = 10) of radioactivity migrated as the 15-keto-13,14-dihydro metabolite. [3H]PGF2alpha uptake decreased upon treatment with probenecid (1 mM) (T/M, 2.5 +/- 0.2; n = 10) or after adding unlabelled PGF2alpha to the medium (1-60 microM) (T/M at 60 microM, 1.8 +/- 0.1; n = 13). The yield of labelled metabolite was also lower when using excess PGF2alpha (14% of control at 60 microM; n = 13), while it was not affected by probenecid. Uptake of both PGs did not change through development, from 0.7 gestation to day 18 postnatal, and attained higher values in the pregnant adult. Conversely, PGF2alpha catabolism decreased postnatally and became negligible by adult age. We conclude that during the perinatal period PGs can be removed from CSF by two distinct processes in the choroid plexus, active transport and catabolism. Neither process, however, can account for the birth-related change in CSF PGE2.

Aging↗
PubMed2000

Differential uptake and catabolism of prostaglandin (PG)E(2) versus PGF(2alpha) in the sheep choroid plexus during development.

The early postnatal decrease in prostaglandin (PG)E(2) levels in cerebrospinal fluid (CSF) likely contributes to the establishment of continuous breathing. To elucidate mechanisms underlying this event, choroid plexuses from lateral (L-CP) and third/fourth (III/IV-CP) ventricles were incubated with [3H]-PGE(2) and label uptake (tissue-to-medium ratio for radioactivity, T/M) and catabolism (%radioactivity associated with metabolites, PGM) were measured. [3H]-PGF(2alpha) was a reference. Uptake of [3H]-PGE(2) was lower than [3H]-PGF(2alpha) in the term fetus (L-CP: 5.9+/-0.5 vs. 9.6+/-0. 9, n=11; III/IV-CP: 2.7+/-0.4 vs. 7.7+/-1.0, n=5) and 17 d lamb (L-CP: 5.3+/-0.8 vs. 11.0+/-1.2, n=7; III/IV-CP: 3.1+/-0.2 vs. 11. 6+/-2.8, n=3 and 4, respectively). This difference was not significant in the pregnant adult. Release of the two compounds was similar and did not change with age. [3H]-PGE(2) uptake was reduced by probenecid (1 mM) and excess PG (60 microM PGE(2) or PGF(2alpha)). Excess PG also reduced catabolism in the fetus, which was extensive for [3H]-PGE(2) and [3H]-PGF(2alpha)60%). In the lamb, catabolism remained high for [3H]-PGE(2) (L-CP: 64+/-4%, n=7; III/IV-CP: 41+/-4%, n=3), but not [3H]-PGF(2alpha) (L-CP: 26+/-4%, n=7; III/IV-CP: 4+/-1%, n=4). In the pregnant adult, catabolism was above background only for [3H]-PGE(2) in the L-CP (26+/-5%, n=11). Unlike the perinatal animal, this catabolism was reduced by probenecid. In conclusion, PGE(2) uptake and catabolism operate independently in the choroid plexus from perinatal sheep. Differences between PGE(2) and PGF(2alpha) are developmentally-regulated for both mechanisms. While neither process explains the postnatal decrease in CSF PGE(2), both may help keep CSF levels low during early postnatal development.

Adult↗
PubMed2002

Role of human organic anion transporter 4 in the transport of ochratoxin A.

The purpose of this study was to investigate the characteristics of ochratoxin A (OTA) transport by multispecific human organic anion transporter 4 (hOAT4) using mouse proximal tubule cells stably transfected with hOAT4 (S(2) hOAT4). Immunohistochemical analysis revealed that hOAT4 protein was localized to the apical side of the proximal tubule. S(2) hOAT4 expressed hOAT4 protein in the apical side as well as basolateral side and the cells were cultured on the plastic dish for experiments. S(2) hOAT4 exhibited a time- and concentration-dependent, and a saturable increase in OTA uptake, with an apparent K(m) value of 22.9+/-2.44 microM. The OTA uptakes were inhibited by several substrates for the OATs. Probenecid, piroxicam, octanoate and citrinin inhibited OTA uptake by hOAT4 in a competitive manner (K(i)=44.4-336.4 microM), with the following order of potency: probenecid > piroxicam > octanoate >citrinin. The efflux of OTA by S(2) hOAT4 was higher than that by mock. Addition of OTA resulted in slight decrease in viability of S(2) hOAT4 compared with mock. These results indicate that hOAT4 mediates the high-affinity transport of OTA on the apical side of the proximal tubule, whereas the transport characteristics of OTA are distinct from those by basolateral OATs.

Animals↗
PubMed1997

Renal transepithelial secretion of ochratoxin A in the non-filtering toad kidney.

Renal excretion is an important way of elimination for the nephrotoxin ochratoxin A (OTA). Because binding to proteins hinders filtration, excretion is mainly due to proximal tubular secretion. The goal of this study was to investigate the kinetics of secretion as well as the extent of urine and tissue accumulation in situ using the non-filtering amphibian kidney model. Transepithelial secretion is a saturable process (K(m) = 0.63.10(-6) mol/l) and leads to a concentration-dependent accumulation of OTA in the tubular lumen and in renal tissue. Maximum accumulation achieved is approximately 14-fold as compared to the perfusate concentration. There was no accumulation in the tubular lumen as compared to renal tissue (lumen-to-tissue concentration ratio approximately 1). Tissue and tubular lumen accumulation were reduced to approximately 40% of control in the presence of 10(-3) mol/l p-aminohippurate (PAH). Addition of 10(-3) mol/l alpha-ketoglutarate (KG) to PAH-containing perfusate did not lead to a further reduction of secretion. By contrast, addition of 10(-2) mol/l L-phenylalanine (L-Phe) reduced secretion further to approximately 25% of control. In the presence of 10(-3) mol/l probenecid tissue accumulation was reduced to 7% and tubular lumen accumulation to 1% of control. Lumen-to-tissue concentration ratio decreased to 0.15 in the presence of probenecid, indicating an inhibitory action at the luminal membrane. Addition of albumin to the perfusate, reduced secretion to only 50% of control, whereas the concentration of free OTA was reduced below 1% as compared to control. The results of this study show that transepithelial secretion is an effective way for accumulation of OTA in the tubular lumen and thus its urinary excretion. Transport via the basolateral organic anion and a basolateral amino acid carrier are the active steps in transepithelial secretion. Luminal exit of OTA is a passive process. Furthermore, tissue accumulation by the active transport across the basolateral membrane supports the toxic action of OTA on proximal tubular cells. Due to the qualitative similarity of organic anion transport our findings should also apply for the mammalian kidney.

Animals↗
PubMed1999

Complete two-dimensional separation for analysis of acidic compounds in plasma using column-switching reversed-phase liquid chromatography.

A complete two-dimensional separation technique for the determination of acidic compounds in plasma was developed by using column-switching reversed-phase liquid chromatography. This technique was based on solute peak enrichment at the top of the second column during heart-cutting and an ion-pair chromatographic separation in the second column using tetrabutylammonium ion, where different separation modes in the first and second columns and solute peak enrichment at the top of the second column during heart-cutting were achieved coincidentally. Retention behaviors of two solutes, zidovudine-beta-D-glucuronide (AZT-beta-D-Gluc) and probenecid, in the first and second column and solute peak enrichment at the top of the second column were investigated for establishment of the system. Different retention behaviors of the solutes in the first and second column, which were evaluated by changes in capacity factor versus acetonitrile concentration in the mobile phases, and peak enrichment could be accomplished by using ion-pair chromatography in the second column. System suitability was confirmed by assessing the number of theoretical plates (N) of the second column for the solutes after heart-cutting. The N values in the second column after column switching were almost same as those in the case that the solutes were directly injected onto the second column. These results indicate that complete two-dimensional separation should be achieved by using this system. Furthermore, this technique was applied to method development for the determination of AZT-beta-D-Gluc and probenecid in rat plasma. The peaks of each analyte in the plasma extract obtained by deproteinization were well separated from those of endogenous substances, and easy determination of the analytes could be accomplished at the ng/ml level only by changing the acetonitrile concentration in the mobile phases.

Acids↗