Nuclear receptor and nuclear receptor target gene messenger ribonucleic acid levels at different sites of the gastrointestinal tract and in liver of healthy dogs

Nuclear receptors (NR) are ligand-activated transcription factors that regulate different metabolic pathways by influencing the expression of target genes. The current study examined mRNA abundance of NR and NR target genes at different sites of the gastrointestinal tract (GIT) and the liver of healthy dogs (Beagles; n = 11). Samples of GIT and liver were collected postmortem and homogenized, total RNA was extracted and reverse transcribed, and gene expression was quantified by real-time reverse-transcription PCR relative to the mean of 3 housekeeping genes ([beta]-actin, glyceraldehyde-3-phosphate dehydrogenase, and ubiquitin). Differences were observed (P [less than or equal to] 0.05) in the mRNA abundance among stomach (St), duodenum (Du), jejunum (Je), ileum (I1), and colon (Col) for NR [pregnane X receptor (Du, Je > I1, Col > St), peroxisome proliferator-associated receptor [gamma] (St, Du, Col > Je, I1), constitutive androstane receptor (Je, Du > I1, Col), and retinoid x receptor a (Du > I1)] and NR target genes [glutathione-S-transferase A3-3 (Du > Je > St, I1; St > Col), phenol-sulfating phenol sulfotransferase 1A1 (Du, Je > I1, St; Col > St), cytochrome P450 3A12 (Du, Je > St, I1, Col), multiple drug resistance gene 1 (Du, Je, I1, Col > St), multiple drug resistance-associated protein 2 (Je, Du > I1 > St, Col), multiple drug resistance-associated protein 3 (Col > St > I1; Du > Je, I1; St > I1), NR corepressor 2 (St > I1, Col), and cytochrome P450 reductase (St, Du, Je > I1, Col)], but not for peroxisome proliferator-associated receptor [alpha]. Differences (P > 0.05) in mRNA abundance in the liver relative to the GIT were also observed. In conclusion, the presence of numerous differences in expression of NR and NR target genes in different parts of the GIT and in liver of healthy dogs may be associated with location-specific functions and regulation of GIT regions. Key words: canine, gastrointestinal tract, liver, nuclear receptor, nuclear receptor target gene, reverse-transcription polymerase chain reaction