RESUMO
The role of the transporter P-glycoprotein (P-gp) in the disposition kinetics of different drugs therapeutically used in veterinary medicine has been demonstrated. Considering the anatomo-physiological features of the ruminant species, the constitutive expression of P-gp (ABCB1) along the sheep gastrointestinal tract was studied. Additionally, the effect of repeated dexamethasone (DEX) administrations on the ABCB1 gene expression in the liver and small intestine was also assessed. The ABCB1 mRNA expression was determined by real-time quantitative PCR. P-gp activity was evaluated in diffusion chambers to determine the efflux of rhodamine 123 (Rho 123) in the ileum from experimental sheep. The constitutive ABCB1 expression was 65-fold higher in the liver than in the intestine (ileum). The highest ABCB1 mRNA expression along the small intestine was observed in the ileum (between 6- and 120-fold higher). The treatment with DEX did not elicit a significant effect on the P-gp gene expression levels in any of the investigated gastrointestinal tissues. Consistently, no significant differences were observed in the intestinal secretion of Rho 123, between untreated control (Peff S-M = 3.99 × 10(-6) ± 2.07 × 10(-6) ) and DEX-treated animals (Peff S-M = 6.00 × 10(-6) ± 2.5 × 10(-6) ). The understanding of the efflux transporters expression and activity along the digestive tract may help to elucidate clinical implications emerging from drug interactions in livestock.
Assuntos
Membro 1 da Subfamília B de Cassetes de Ligação de ATP/metabolismo , Regulação da Expressão Gênica/fisiologia , Intestino Delgado/metabolismo , Fígado/metabolismo , Ovinos/fisiologia , Membro 1 da Subfamília B de Cassetes de Ligação de ATP/genética , Animais , Masculino , RNA Mensageiro/genética , RNA Mensageiro/metabolismoRESUMO
The effects of repeated administrations of dexamethasone (DEX) (3 mg/kg/day by i.m. route for 7 days) on the gene expression profile of a cytochrome P450 (CYP) 3A28-like isoenzyme, on the expression of a CYP3A-immunoreactive protein and on CYP3A-dependent metabolic activities in sheep liver and small intestinal mucosa were evaluated in the current work. CYP 3A-dependent metabolic activities (erythromycin and triacetyl-oleandomycin N-demethylations) were assessed in microsomal fractions. The mRNA expression of CYP3A28-like, glucocorticoid receptor, constitutive androstane receptor, pregnane X receptor and retinoic X receptor alpha (RXRα) was determined by quantitative real-time PCR. The expression of a CYP3A-immunoreactive protein was measured by Western blot analyses. In the liver, DEX treatment increased CYP3A28-like mRNA levels (2.67-fold, P<0.01) and CYP3A apoprotein expression (1.34-fold, P<0.05) and stimulated CYP3A-dependent metabolism. High and significant correlation coefficients between CYP3A-dependent activities and CYP3A28-like gene (r=0.835-0.856, P<0.01) or protein (r=0.728-0.855, P<0.05) expression profiles were observed. Among the transcriptional factors, DEX only stimulated (2.1-fold, P<0.01) the mRNA expression of RXRα. In sheep small intestine, DEX caused a slight increment (34.6%, P<0.05) in erythromycin N-demethylase activity in the jejunal mucosa and a significant enhancement (P<0.05) of CYP3A apoprotein level in the duodenal mucosa.