Capsaicin-sensitive primary afferent (CSPA) fibers are involved in the regulation of glucose transport and the expression of its transporters in the small intestine in rats

Abstract

Previous studies have shown that CSPA fibers are involved in the regulation of alanine absorption in the small intestine. However, their effect on glucose absorption has not been yet fully characterized. This study examines the effect of CSPA fibers on glucose absorption and determines their effect on mRNA expression of glucose transporters (GLUT). Glucose absorption was measured in a jejunal segment perfused with 20mM glucose using the single-pass perfusion technique. CSPA ablation was achieved by subcutaneous injections of 1% capsaicin under light anesthesia at different time intervals. Sham rats received vehicle injections. Two weeks post-treatment, 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 sodium-glucose cotransporter (SGLT1), GLUT2 and Na+-K+-ATPase were determined in jejunal samples by real-time PCR with actin as the housekeeping gene. A 14-fold increase in SGLT1 and a 7-fold increase in Na+-K+-ATPase mRNA expression were detected in capsaicin-treated rats as compared to sham. No significant increase in GLUT2 mRNA expression was noted in capsaicin-treated rats. Our results show that 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.