Non-cholinergic neural excitation of the human rectum induced by acetorphan, an inhibitor of enkephalinase.

We have studied the effects of acetorphan, an inhibitor of enkephalinase, on the electrical activity of human rectum. Acetorphan activated the rectum of healthy volunteers by inducing bursts of spike potentials, this activation might become cyclical. In contrast, this drug failed to modify the motility of the aganglionic portion of the rectum in one case of Hirschsprung's disease, indicating that the effect of acetorphan involves the intramural plexuses. Activation of the rectum persisted in spite of the blockade of the cholinergic excitatory pathways by atropine, which confirms the existence of an excitatory non-cholinergic mechanism for the rectum. Our results also suggest that the neurotransmitter responsible for this effect is continuously released by the nervous structures implicated in the control of rectal motility. Immunohistochemical data show that the rectum is supplied by a rich enkephalinergic innervation.