The effect of experimental colitis on water absorption and aquaporin expression in the small intestine in rats

Abstract

Previous studies have investigated the effect of experimental colitis on nutrient and fluid absorption in the jejunum in rats. However, its effect on water absorption and aquaporin expression has not been yet fully characterized. This study examines the effect of experimental colitis on jejunal water absorption and the expression of AQPs mRNA and proteins in the small intestine in rats. Colitis was induced in rats via 2 chemicals: Iodoacetamide (IA) and Trinitrobenzenesulfonate (TNBS). Sham rats received vehicle treatment. Two days post induction, jejunal water absorption decreased by 32% in TNBS models and 34% in IA models compared to normal/sham animal models. Seven days post induction, water absorption tends to return to normal. mRNA expression of AQP1, AQP4, AQP7, and AQP8 in the jejunum and ileum two days post induction by real-time PCR with actin as the housekeeping gene. Overall, there was no variation in the mRNA expression of AQPs in the jejunum and ileum compared to sham/normal. However, there was a decrease in protein expression in the jejunum and ileum 2 days post induction. Seven days post induction; there was no variation in mRNA expression of aquaporins in jejunum and ileum compared to sham/normal. AQPs protein expression returned to normal in the jejunum 7 days post induction. However, AQPs protein expression was still lower than normal/sham expression in the ileum. Thus, experimental colitis decreased water absorption and the expression of AQP in the small intestine in rats. Previous studies have shown an increase in cytokine levels in the small intestine although no inflammation was detected there. Moreover, cytokines were shown to decrease aquaporin expression by posttranscriptional modifications, and affect the ENS. Our results show a crosstalk between the inflamed colon and the small intestine. We suggest that the functional adaptation that has occurred in the small intestine for water absorption after colitis induction could be mediated by the cytokines directly through their effect on aquaporin, and/ or indirectly by affecting the ENS.