Figure 9.
Schematic representation of the effect of Ang II in colonic reactivity along the colon of control (top panel) and TNBS-induced rats (bottom panel). Ang II activates AT1 receptors, contracting all colonic regions of control and TNBS-induced rats. Ang II also activates AT2 receptors along the colon of control animals, promoting colonic relaxation, but this effect is not observed in TNBS-induced rats. Animals with TNBS-induced colitis show higher tissue concentration of endogenous Ang II and decreased expression of AT1 receptors but similar expression of AT2 receptors. The intricate, Ang II-mediated colonic contraction involves a neuronal inhibitory component and a non-neuronal excitatory component. The neuronal component involves activation of muscarinic receptors and production of NO. The non-neuronal component includes activation of EGC and/or ICC, dependent on the colonic region. EGC—enteric glial cells; ICC—interstitial cells of Cajal; M—muscarinic receptor; NO—nitric oxide; (+)—excitatory mechanism; (−)—inhibitory mechanism.