Role of capsaicin-sensitive primary afferent fibers in the regulation of glucose transport and the expression of its transporters in the small intestine in rats

Abstract

Previous studies have shown that capsaicin-sensitive primary afferent (CSPA) fibers are involved in the regulation of alanine absorption in the small intestine in rats. However, their effect on glucose absorption has not been yet fully characterized. This study examines the effect of CSPA fibers on glucose absorption and the mRNA expression of glucose transporters in the small intestine in rats. Jejunal glucose absorption was measured via the in-vivo single-pass perfusion technique. CSPA fiber ablation was achieved by subcutaneous injections of 1% capsaicin at different time intervals. Sham rats received vehicle injections. Two weeks posttreatment, verification of desensitization was done by standard method. Glucose absorption in the jejunum showed a 68% increase in capsaicin-treated rats compared to sham. mRNA expressions of SGLT1, GLUT2, GLUT5 and Na+ -K+ -ATPase were determined in jejunal samples by real-time PCR with actin as the housekeeping gene. An increase in SGLT1 and Na+ -K+ -ATPase mRNA expression was detected in capsaicin-treated rats compared to sham. No significant increase in GLUT2 and GLUT5 mRNA expression was noted in capsaicin-treated rats. Thus, ablation of CSPA fibers increased glucose absorption by increasing the expression of its transporter. This indicates that CSPA fibers exercise an inhibitory tone in the small intestine that regulates epithelial absorption of glucose. Investigators in our lab have shown that a functional adaptation for glucose absorption takes place in the small intestine in rats post-total colectomy that leads the small intestine to modulate its glucose absorptive capacity. In order to investigate whether this crosstalk between the small intestine and the colon is mediated via CSPA fibers, colectomy or sham surgery was performed 2 weeks post-treatment with capsaicin. Glucose absorption in the jejunum was measured via the in-vivo single-pass perfusion technique, and mRNA expressions of SGLT1, GLUT2, GLUT5 and Na+ -K+ -ATPase were determined in jejunal samples by real-time PCR with actin as the housekeeping gene. No significant variation in glucose absorption or mRNA expression of glucose transporters was detected in capsaicintreated and colectomized rats compared to capsaicin-treated and sham rats. Our results suggest that the functional adaptation that has occurred in the small intestine for glucose absorption after total colectomy is neurally mediated, and that vagal CSPA fibers may mediate the crosstalk that exists between the small intestine and the colon post-total colectomy.