An Inhibitory Component of the Response to Distension of Rat Ileum

Abstract

THERE is good evidence that the longitudinal smooth muscle of small and large intestine of rat, mouse, guinea-pig and rabbit is supplied with inhibitory nerves arising from intrinsic neurones which are probably components of the myenteric plexus^1,2. These inhibitory nerves can be excited by transmural stimulation of segments of intestine², by ‘field’ stimulation of strips of intestinal muscle¹, or by ganglion stimulants such as dimethyl-4-phenyl-piperazinium iodide (DMPP)^1,2. The relaxation of the longitudinal muscle mediated by these nerves can always be observed in the presence of atropine, 1 µg/ml., which blocks any muscarinic excitatory effects due to stimulation of cholinergic nerve fibres within the wall of the intestine. Since the inhibitory response is unaffected by concentrations of guanethidine and bretylium which block the relaxation in response to perivascular nerve stimulation, it seems likely that the intrinsic inhibitory system is distinct from the sympathetic system. The conditions which cause reflex activation of the intrinsic inhibitory neurones, in vivo, remain to be clarified.