Induction of rat intestinal P-glycoprotein by spironolactone and its effect on absorption of orally administered digoxin.

The effect of the diuretic spironolactone (SL) on expression and function of intestinal P-glycoprotein (P-gp), as well as its impact on intestinal absorption of digoxin, was explored. Rats were treated with daily doses of 200 micromol/kg b.wt. of SL intraperitoneally for 3 consecutive days. The small intestine was divided into four equal segments of approximately 25 cm, with segment I being the most proximal. Brush-border membranes were isolated and used in analysis of P-gp expression by Western blot analysis. P-gp content increased in the SL group by 526, 292, 210, and 622% over controls for segments I, II, III, and IV, respectively. Up-regulation of apical P-gp was confirmed by immunofluorescence microscopy. P-gp transport activity was explored in intestinal sacs prepared from segment IV using two different model substrates. Serosal to mucosal transport (efflux) of rhodamine 123 was 140% higher, and mucosal to serosal transport (absorption) of digoxin was 40% lower in the SL group, both indicating increased P-gp function. In vivo experiments showed that intestinal absorption of a single dose of digoxin administered p.o. was attenuated by SL pretreatment. Thus, concentration of digoxin in portal and peripheral blood was lower in SL versus control groups, as well as its accumulation in kidney and liver. Urinary excretion of digoxin was significantly decreased in the SL group, probably reflecting decreased systemic availability of digoxin for subsequent urinary elimination. We conclude that SL induces P-gp expression with potential impact on intestinal absorption of substrates with therapeutic application.

Effect of acetaminophen on expression and activity of rat liver multidrug resistance-associated protein 2 and P-glycoprotein.

We evaluated the effect of acetaminophen (APAP), given as a single, 1g/kg body weight dose, on expression and activity of rat liver multidrug resistance-associated protein 2 (Mrp2) and P-glycoprotein (P-gp), two major canalicular drug transporters. The studies were performed 24h after administration of the drug. APAP induced an increase in plasma membrane content of Mrp2 detected by western blotting, consistent with increased detection of the protein at the canalicular level by immunoflourescence microscopy. In vivo biliary excretion of dinitrophenyl-S-glutathione, a well known Mrp2 substrate, was slightly but significantly increased by APAP, agreeing well with upregulation of the transporter. Basal biliary excretion of oxidized glutathione, an endogenous Mrp2 substrate, was also increased by APAP, likely indicating increased hepatic synthesis as a result of APAP-induced oxidative stress followed by accelerated canalicular secretion mediated by Mrp2. APAP also increased the expression of P-gp detected by western blotting and immunofluorescence microscopy as well as the in vivo biliary secretory rate of digoxin, a model P-gp substrate. Because specific APAP-conjugated metabolites are Mrp2 substrates, we postulate that induction of Mrp2 by APAP may represent an adaptive mechanism to accelerate liver disposition of the drug. In addition, increased Mrp2-mediated elimination of oxidized glutathione may be essential in maintaining the redox equilibrium in the hepatocyte under conditions of APAP-induced oxidative stress.

La sobredosis de paracetamol y la colestasis experimental inducen la expresión de los genes que codifican la P-glicoprotína tipo 1 en ratas / Paracetamol overdose and experimental cholestasis induced gene expresion that codified P-glicoprotein tipe 1 in rats

Excretion of lipophilic cationic toxic compounds from the interior of the hepatocyte to the bile is mediated by P-Glycoprotein. It is an integral protein located in the bile canaliculi. The present work study the hepatic expression of P-Glycoprotein in different models of experimental liver disease: Acute paracetamol intoxication, extrahepatic cholestasis and cholestasis followed by acute paracetamol intoxication. mRNA was isolated from liver tissue, and the expression of Pg-p was assessed by Northern blot. It is concluded that the hepatic expression of mdr1b is increased in the experimental liver diseases when compared to controls. On the other hand, mdr2 expression was similar between the different groups (AU)

La sobredosis de paracetamol y la colestasis experimental inducen la expresión de los genes que codifican la P-glicoprotína tipo 1 en ratas / Paracetamol overdose and experimental cholestasis induced gene expresion that codified P-glicoprotein tipe 1 in rats

Excretion of lipophilic cationic toxic compounds from the interior of the hepatocyte to the bile is mediated by P-Glycoprotein. It is an integral protein located in the bile canaliculi. The present work study the hepatic expression of P-Glycoprotein in different models of experimental liver disease: Acute paracetamol intoxication, extrahepatic cholestasis and cholestasis followed by acute paracetamol intoxication. mRNA was isolated from liver tissue, and the expression of Pg-p was assessed by Northern blot. It is concluded that the hepatic expression of mdr1b is increased in the experimental liver diseases when compared to controls. On the other hand, mdr2 expression was similar between the different groups

[Paracetamol overdose and experimental cholestasis induced gene expression regulation that codified P-Glycoprotein type 1 in rats]. / La sobredosis de paracetamol y la colestasis experimental inducen la expresión de los genes que codifican la P-glicoprotína tipo 1 en ratas.

Excretion of lipophilic cationic toxic compounds from the interior of the hepatocyte to the bile is mediated by P-Glycoprotein. It is an integral protein located in the bile canaliculi. The present work study the hepatic expression of P-Glycoprotein in different models of experimental liver disease: Acute paracetamol intoxication, extrahepatic cholestasis and cholestasis followed by acute paracetamol intoxication. mRNA was isolated from liver tissue, and the expression of Pg-p was assessed by Northern blot. It is concluded that the hepatic expression of mdr1b is increased in the experimental liver diseases when compared to controls. On the other hand, mdr2 expression was similar between the different groups.

La sobredosis de paracetamol y la colestasis experimental inducen la expresión de los genes que codifican la P-glicoprotína tipo 1 en ratas. / [Paracetamol overdose and experimental cholestasis induced gene expression regulation that codified P-Glycoprotein type 1 in rats]

Excretion of lipophilic cationic toxic compounds from the interior of the hepatocyte to the bile is mediated by P-Glycoprotein. It is an integral protein located in the bile canaliculi. The present work study the hepatic expression of P-Glycoprotein in different models of experimental liver disease: Acute paracetamol intoxication, extrahepatic cholestasis and cholestasis followed by acute paracetamol intoxication. mRNA was isolated from liver tissue, and the expression of Pg-p was assessed by Northern blot. It is concluded that the hepatic expression of mdr1b is increased in the experimental liver diseases when compared to controls. On the other hand, mdr2 expression was similar between the different groups.