INVOLVEMENT OF NITRIC-OXIDE IN EXTRINSIC NERVOUS CONTROL OF ILEAL CONTRACTILE ACTIVITY

The experiments were carried out on guinea pig mesenteric nerve-ileal preparations (ileal segments with mesenteric nerves originating from t he superior mesenteric ganglion) isolated at various distances from th e ileocecal junction (ICJ). Contractile activity was recorded in the p resence of hexamethonium (50 mu M). On the background of electrical fi eld stimulation (EFS; 0.1 Hz, 0.5 ms, supramaximal current intensity)- induced twitch contractions, the mesenteric nerve stimulation (MNS; fr equency of 2-30 Hz, 0.5 ms, supramaximal current intensity, 20-s train s) exerted two types of effects, depending on the distance from ICJ at which the preparations were isolated and on the pulse frequency. In p reparations isolated from the ileum at a distance of 20 cm from ICJ, M NS at all the frequencies studied inhibited the EFS-induced twitch con tractions, reaching the maximum at 30 Hz. In preparations isolated fro m the terminal ileum at a distance of 10 cm from ICJ, MNS at 20 Hz and 30 Hz decreased the twitch contraction amplitude, whereas MNS at 2-10 Hz produced an increase in the tone on which twitch contractions with reduced amplitude were superimposed. The finding that guanethidine (5 mu M) eliminated the MNS twitch inhibition provides evidence for the adrenergic origin of the latter. The nitric oxide synthase inhibitor N -omega-nitro-L-arginine (100 mu M) was efficient in reducing the MNS t witch inhibition but only at low-frequency (5 Hz) MNS (9 < 0.05). Our results suggest the participation of nitric oxide in the nervous contr ol exerted by the superior mesenteric ganglion over the ileal contract ile activity. (C) 1998 Elsevier Science Inc.