Intestinal chronic obstruction affects motor responsiveness of rat hypertrophic longitudinal and circular muscles

Extensive morphological and neurochemical changes have been experimentally and clinically documented in the hypertrophied intestine located orally to a chronic partial stenosis of the lumen. Functional studies revealed not only disruption of the interdigestive motor complex in vivo and decreased efficiency of contraction but also preservation of the peristaltic reflex in vitro. Given the critical role played in intestinal peristalsis by the coordinated activity of the longitudinal (LM) and circular muscle (CM), this work focuses on the motor responses of LM and CM isolated from rat hypertrophied ileum following mechanical obstruction. Maximal contractions to both receptor (acetylcholine and substance P) and non-receptor (K+) mediated stimuli were up to 10-fold increased in hypertrophic CM rings compared with control tissues, while a higher potency of substance P was revealed in both hypertrophied muscle layers. Relaxations to vasoactive intestinal polypeptide and 8-Br-cGMP were more intense on prostaglandin F(2alpha)-contracted hypertrophic LM strips compared with control tissues and a general tendency towards increased relaxation was shared also by hypertrophic CM basal tone. The present results collectively suggest that hypertrophic growth leads to hyperresponsiveness to contractile agents, particularly evident in the CM, and to increased sensitivity to relaxing mediators, especially exhibited by the LM. In this regard, the complementary role exerted by each muscle layer and the plasticity of the intestinal tissue could both come into play to preserve the intestinal functions in a changing environment.