Organic Anions In Rats Research Articles

Gender‐specific expression of liver organic anion transporters in rat

Sex differences in drug pharmacokinetics have been well recognized and gender has been considered a risk factor for adverse events to medications. The aim of this study was to investigate the effect of gender on the expression of hepatocellular transport proteins involved in uptake and secretion of organic anions in rat. Expression of the rat liver organic anion transporting polypeptides (Oatps) and multidrug resistance proteins (Mrps) was analysed by reverse transcription polymerase chain reaction (RT-PCR), immunoblot analysis and immunofluorescence microscopy in male and female rats. Regulation of these transport proteins in response to the steroid dehydroepiandrosterone (DHEA) was investigated. In untreated rats, protein expression significantly differed between genders being higher (Mrp2, Mrp3), comparable [Oatp1a1 (Oatp1); Oatp1b2 (Oatp4)] or lower [Oatp1a4 (Oatp2)] in female than in male rat. DHEA treatment over 3 days (100 mg d(-1)) led to a further increase in Mrp3 expression only in female rats. Mrp2 expression was not influenced by DHEA treatment. Oatp1a1 and Oatp1b2 were significantly down-regulated after DHEA treatment in both male and female rats. In contrast, Oatp1a4 was down-regulated in male rats only. In rat, liver transport proteins of the Oatp and Mrp family are expressed and regulated in a gender-specific manner according to sexual differences in the hepatic metabolism of steroids and drugs. These findings may partly explain the well-known sex differences in hepatic handling of organic anions.

Altered renal elimination of organic anions in rats with chronic renal failure

The progress of chronic renal failure (CRF) is characterized by the development of glomerular and tubular lesions. However, little is known about the expression of organic anions renal transporters. The objective of this work was to study, in rats with experimental CRF (5/6 nephrectomy), the expression of the organic anion transporter 1 (OAT1) and organic anion transporter 3 (OAT3) and their contribution to the pharmacokinetics and renal excretion of p-aminohippurate (PAH). Two groups of animals were used: Sham and CRF. Six months after surgery, systolic blood pressure and plasma creatinine concentrations were significantly higher in CRF groups. CRF rats showed a diminution in: the filtered, secreted and excreted load of PAH; the systemic clearance of PAH; the renal OAT1 expression; and the renal Na-K-ATPase activity. No remarkable modifications were observed in the OAT3 expression from CRF kidneys. The diminution in the systemic depuration and renal excretion of PAH may be explained by the decrease in its filtered and secreted load. The lower OAT1 expression in remnant renal mass of CRF rats or/and the lower activity of Na-K-ATPase might justify, at least in part, the diminished secreted load of this organic anion.

Biliary excretion of bile acids and organic anions in rats with dichloroethylene-induced bile canalicular injury

Hepatocytes in zone 1 of the hepatic lobule play a role in the uptake and biliary excretion of bile acids and organic anions under physiological conditions, and hepatocytes in zone 3 may play a role only when there is a high-dose load. To further elucidate the role of hepatic zonation in the hepatic handling of bile acids and organic anions, the biliary excretion of these compounds was studied in rats with dichloroethylene (DCE)-induced selective zone 3 bile canalicular injury. Biliary excretion of various bile acids and organic anions was studied in rats 1 h after oral administration of DCE (5 mg/100 g). The effect of DCE on the immunostaining of multidrug resistance protein 2 (Mrp2; an important canalicular organic anion transporter) in the liver was also examined. The biliary excretory maximum of taurocholate and tauroursodeoxycholate was decreased in DCE-treated rats, whereas the biliary excretion of taurolithocholate-sulfate and phenolphthalein-glucuronide was unchanged in DCE-treated rats, and DCE treatment decreased the biliary excretion of sulfobromophthalein and pravastatin. DCE decreased Mrp2 staining in the canalicular membrane of zone 3 hepatocytes on immunohistochemistry. These findings indicate that canalicular transport in zone 3 hepatocytes is important in the biliary excretion of bile acids and organic anions, when they are administered at high doses.

Gender-Specific Expression of Liver Organic Anion Transporters and their Differential Regulation after DHEA Treatment in Rat

Background & Aims : Sex differences in drug pharmacokinetics have been well recognized and gender has been considered a risk factor for adverse events to medications yet the underlying mechanisms are incompletely understood. The aim of this study was to investigate the effect of gender and dehydroepiandrosterone (DHEA) treatment on the expression of hepatocellular transport proteins involved in uptake and secretion of organic anions in rat. Methods: Expression of the rat liver organic anion transporting polypeptides (Oatps) and multidrug resistance proteins (Mrps) was analyzed by RT-PCR, immunoblot analysis and immunofluorescence microscopy in male and female rats. Regulation of these transport proteins in response to DHEA feeding was investigated. Results: In untreated rats, protein expression significantly differed between genders being higher [Mrp2; Mrp3; Oatp1b2 (Oatp4)] comparable [Oatp1a1 (Oatp1);] or lower [Oatp1a4 (Oatp2)] in female than in male rat. DHEA treatment led to a further increase in Mrp3 expression only in female rats. Mrp2 expression was not influenced by DHEA treatment. In contrast, Oatp1b2 (Oatp4) and Oatp1a1 (Oatp1) were significantly down-regulated after DHEA feeding in both male and female rats. Conclusions: In rat, liver transport proteins of the Oatp and Mrp family are expressed in a gender-specific manner and are differentially regulated in response to DHEA feeding. Down-regulation of uptake transporters and up-regulation of the export pump Mrp3 after DHEA feeding suggests a substrate-dependent feedback regulation. These findings may in part explain the well-known sex differences in hepatic handling of organic anions.

Renal elimination of organic anions in rats with bilateral ureteral obstruction.

Urinary tract obstruction is an important cause of acute renal failure. Several abnormalities in renal tubular function may occur in obstructive nephropathy. The tubular secretion of organic anions is an important function of the kidney that eliminates potentially toxic organic anions from the body, however, the mechanisms involved in organic anions renal elimination in rats with bilateral ureteral obstruction (BUO) have not been elucidated. In this study, it was evaluated the renal handling of p-aminohippurate (PAH) in adult male Wistar rats with BUO. A diminished renal clearance of PAH was observed in BUO rats as consequence of a diminution in the secreted load of this organic anion. The increase in the abundance of organic anions transporter 1 (OAT1) and the absence of modification in cortical renal blood flow, measured with fluorescence microspheres, do not explain the altered secretion of PAH. The diminished Na,K-ATPase activity in cortex from obstructed kidneys might condition OAT1 function. Additionally, it is also possible to conclude that in the presence of BUO, PAH clearance is not a good estimate of renal plasma flow.

Effects of lipopolysaccharide on the biliary excretion of bile acids and organic anions in rats.

Lipopolysaccharide is known to be a cause of cholestasis associated with sepsis. It has also recently been reported to down-regulate the basolateral and canalicular transporters. The aim of the present study was to examine simultaneously the effect of lipopolysaccharide on the biliary excretion of typical substrates of bile salt export pump and multidrug resistance protein 2 in vivo, and the effect of lipopolysaccharide on the amount of these transporters. After intravenous administration of O127:B8-derived lipopolysaccharide (2.5 mg/kg), the biliary excretion of taurocholate and various organic anions was studied, and the protein levels of bile salt export pump and multidrug resistance protein 2 in the crude liver membrane was determined by western blot analysis. Lipopolysaccharide decreased the biliary excretion of tracer amounts of taurocholate, leukotriene C4, taurolithocholate-3-sulfate and temocapril without affecting bile flow. The biliary excretion of high doses of taurocholate and sulfobromophthalein was markedly inhibited by lipopolysaccharide. Lipopolysaccharide decreased bile salt export pump levels in the liver plasma membrane fraction to 48% of control rats, and markedly decreased multidrug resistance protein 2 levels to 17% of control rats. These findings support the hypothesis that down-regulation of the canalicular transporters by lipopolysaccharide causes the impairment of the biliary excretion of bile acids and organic anions in cholestasis of sepsis prior to the decrease of bile flow.

Effect of dexamethasone on biliary excretion of bile acids and organic anions in rats

Multidrug resistance protein 2 (Mrp2) is an important transporter for biliary excretion of organic anions, and is reported to be up-regulated by dexamethasone. In the present study, effect of dexamethazone (1 mg/kg) on biliary excretion of bile acids and organic anions was studied in rats. After bile duct cannulation, bile acids and organic anions were intravenously administered, and their biliary excretion was studied. Biliary excretion of tracer doses of taurocholate and taurolithocholate-sulfate was unchanged with dexamethasone. Dexamethasone increased the excretory maximum of taurolithocholate-sulfate and sulfobromophthalein to 1.8 and 1.5 times, respectively, whereas it did not change the excretory maximum of phenolphthalein-glucuronide and taurocholate. Dexamethasone also increased biliary glutathione excretion. These results obtained by in vivo studies can be explained by the up-regulation of Mrp2, which had been reported in in vitro studies.

Pharmacokinetics of organic anions in rats with arterial calcinosis.

1. Ageing induces calcium accumulation in the vascular system. The simplest experimental way of producing high degrees of arterial calcium overload is by administration of an overdose of vitamin D(3) to rats. The aim of the present study was to evaluate the pharmacokinetics of organic anions in rats with arterial calcinosis induced by an overdose of vitamin D(3). 2. We used bromosulfophthalein (BSP) and sulfanilamide (SA) as models of organic anions with preferential biliary and renal excretion, respectively. 3. Increases in the clearance and elimination rate constant of BSP were observed in treated rats. The clearance and the elimination rate constant for SA were also increased in rats with arterial calcinosis. 4. Variations in arterial hepatic blood flow, aspartate aminotransferase activity and liver calcium accumulation were not observed in treated rats. In contrast, treated rats had a lower renal blood flow and increased renal calcium levels. 5. In summary, rats with arterial calcinosis showed an increase in total body clearance of both BSP and SA, probably associated with modifications in their metabolism and/or in organ extraction. Alterations to hepatic and renal blood flow do not account for these phenomena.

Effects of colchicine and phenothiazine on biliary excretion of organic anions in rats.

Vesicular transport inhibitors have been reported to inhibit biliary excretion of some organic anions, suggesting that vesicular transport has a role in intracellular transport of these compounds. However, these inhibitors are substrates for P-glycoprotein. To examine whether P-glycoprotein has a role in canalicular transport of organic anions in addition to the canalicular multispecific organic anion transporter, we studied the effect of colchicine, a vesicular transport inhibitor, and phenothiazine to increase P-glycoprotein expression on biliary excretion of various organic anions in rats. Colchicine treatment slightly but significantly inhibited biliary excretion of indocyanine green, dinitrophenyl-glutathione and pravastatin, and had no effect on biliary excretion of sulphobromophthalein and dibromosulphophthalein. Phenothiazine treatment did not affect biliary excretion of indocyanine green and pravastatin, but it increased biliary sulphobromophthalein-glutathione excretion. In conclusion, the present findings suggest that P-glycoprotein plays an additive role on biliary excretion of some organic anions in addition to the canalicular multispecific organic anion transporter.

Hepatic disposition of organic anions in rats infested with Fasciola hepatica

This study was undertaken to investigate the effects of subclinical fascioliasis at various stages of its development (3, 6, and 11 weeks after infestation with an oral dose of 20 metacercariae of Fasciola hepatica) on the hepatobiliary transport of organic anions in rats. Basal bile acid secretion was not significantly modified in infested rats as compared to the controls but there was a significantly increased bile flow in the 11-week group. In all infested rats, maximal biliary excretion and cumulative excretion of bromosulphthalein was significantly reduced, although there was a tendence to recovery in the 11-week infested group. Decreased biliary secretion was accompanied by increased plasma and liver concentrations of bromosulphthalein. Glutathione S-transferase activity was significantly reduced by Weeks 3 and 6 postinfestation. Liver glutathione concentration was significantly reduced in all infested rats. Maximal excretion of dibromosulphthalein, a compound not biotransformed in the liver, fell by Week 6 postinfestation and recovered a normal value thereafter. These results indicate that effects of experimentally induced fascioliasis on hepatic disposition of organic anions depend upon the stage of its development and that are a consequence of both metabolism and transport related factors.

Influence of experimental fascioliasis on the hepatic disposition of organic anions in rats

Influence of experimental fascioliasis on the hepatic disposition of organic anions in rats

Effect of N-substituted imidazoles on the hepatic transport of organic anions in rats

Effect of N-substituted imidazoles on the hepatic transport of organic anions in rats

Sex steroid modulation of the hepatic uptake of organic anions in rat

To investigate the role of sex steroids in the sex-related difference in the hepatic uptake of organic anions, sulphobromophthalein (bromsulphalein, BSP) transport was measured in hepatocytes isolated from rats either deprived of hormonal influence by castration at prepubertal age or after hormonal substitution. In control animals, the kinetics of BSP uptake showed the presence of two components: one saturable (0-3 microM), with high affinity and low capacity, and the other linear (9-30 microM), probably related to the non-specific component of BSP uptake. Sex difference was detected only in the saturable portion of the uptake process as the apparent Km was significantly lower in females than in males (3.8 +/- 0.7 vs. 6.1 +/- 1.8 microM, mean +/- S.D. of six animals, P less than 0.01). In contrast, no difference was observed in Vmax (2.3 +/- 0.3 vs. 2.2 +/- 0.7 nmol BSP.(mg protein)-1.min-1). Castration was associated with the disappearance of the saturable uptake site and abolished the sex difference. Progesterone treatment of castrated males failed to restore the saturable kinetics of BSP uptake. In contrast, administration of oestradiol to castrated males or testosterone to castrated females did restore the saturable kinetics of the high-affinity BSP uptake. Km and Vmax were comparable to those of adult females and males, respectively, with the exception of testosterone which induced a Vmax value higher than that observed in the other groups of animals. These data suggest that the influence of oestrogen and testosterone is necessary for the expression of the high-affinity, low-capacity carrier-mediated process of hepatic BSP uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatobiliary transport of organic anions in rats with a genetic hepatic transport defect and UDP-glucuronyl transferase (UDPGT) deficiency

Hepatobiliary transport of organic anions in rats with a genetic hepatic transport defect and UDP-glucuronyl transferase (UDPGT) deficiency

Effects of barbiturates on the hepatic cytochrome P-450 dependent enzyme system and biliary excretion of exogenous organic anions in rats.

Effect of pretreatment (150 mumol/kg i.p. twice daily for 5 days) wtih six barbiturates (barbital, butobarbital, pentobarbital, amobarbital, phenobarbital and thiopental) on the hepatic microsomal drug methabolizing enzyme system and biliary excretion of bromcresol green and bromsulphthalein-glutathione conjugate has been investigated in rats. All six barburates produced microsomal induction. Phenobarbital, thiopental, barbital and butobarbital increased liver weight, biliary flow and biliary excretion of bromcresol green and bromsulphthalein-glutathione conjugate, however, pentobarbital and amobarbital were ineffective in these parameters. Our results seem to indicate that the enhanced biliary excretion of exogenous anions produced by barbiturates is independent of microsomal enzyme induction.

Biopharmaceutical study of the hepato-biliary transport of drugs. IV. Development of the method to investigate the process of the active secretion of drugs from the hepatocytes into the bile canaliculi and its application to the biliary excretion of organic anions in rat.

Biopharmaceutical study of the hepato-biliary transport of drugs. IV. Development of the method to investigate the process of the active secretion of drugs from the hepatocytes into the bile canaliculi and its application to the biliary excretion of organic anions in rat.

Michaelis—menten Kinetic Parameters of Renal Tubular Secretion of para-alkylated Mandelic Acids and Their Use in Revealing Possible Chemical Characteristics around Receptor Site of Secretion Carrier in Rats

From the determination of the Michaelis-Menten kinetic parameters (Vm and Km) of renal tubular secretion of D-(—)-p-n-propylmandelic acid (V) and D-(—)-p-isopropylmandelic acid (VI) in rats, it is shown that these compounds involve the same renal tubular carrier for their secretion but the affinity of V for the carrier is approximately twice that of VI. By considering these parameters as well as the structural variations of V and VI, together with those of other homologs of D-(—)-mandelic acid (I) studied previously, inferences have been drawn regarding the chemical nature around the possible cationic receptor site of the carrier for renal tubular secretion of organic anions in rats. The utilization of the model compounds of a homologous series of I in studying the influence of alkyl groups present in the organic anions on the pharmacokinetic parameters, particularly the volume of distribution, is discussed.