Altered contractility of circular and longitudinal muscle in TNBS-inflamed guinea pig ileum

Intestinal motility disorders are often associated with gut inflammation. We evaluated, in vitro under isometric conditions, changes in contractility of longitudinal and circular muscle layers from guinea pig ileum after 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced ileitis. TNBS treatment did not modify length-active tension relationships for both muscle layers, whereas a significant increase in passive tension was observed in the circular muscle response to stretching. Moreover, in both control and inflamed strips at optimal stretch, concentration-response curves to KCl were similar for both layers. In contrast, contractile responses to receptor agonists were differentially altered in both layers in comparison with controls. Thus, in longitudinal strips fi om TNBS-treated ileum, there was a twofold increase in maximal response (E-max) induced by carbachol and histamine without modification of 50% effective concentration (EC50) values; responses to 5-hydroxytryptamine (5-HT) were not modified; both alpha(1)- and alpha(2)-adrenoceptor-mediated responses to epinephrine were abolished. In circular strips, inflammation did not affect the E-max induced by carbachol and histamine but led to increased EC50 values; E-max to 5-HT was reduced without change in EC50 values. Moreover, in the dose range used (0.1 nM to 0.1 mM), a maximal response to carbachol was not obtained in inflamed circular strips. The results indicate that in the guinea pig model of TNBS-induced ileitis, the in vitro contractile responses of circular and longitudinal smooth muscle to the stimulation of various receptors are differentially altered, whereas non-receptor-mediated contraction to KCl depolarization is not modified.