ROLE OF NITRIC-OXIDE IN SYMPATHETIC NEUROTRANSMISSION IN OPOSSUM INTERNAL ANAL-SPHINCTER

Background: The role of nitric oxide in the gut in response to sympathetic nerve stimulation has not been examined. The present study examined the influence of the NO synthase inhibitor l-NG-nitro-arginine (l-NNA) on responses to hypogastric nerve stimulation (HGNS) in the opossum internal anal sphincter (IAS). Methods: Resting pressures in the IAS (IASP) were monitored using low-compliance continuously perfused catheters. Results: The predominant response to HGNS was an elevation of the resting tone in the IAS. The other responses of infrequent nature were a decrease in the IASP and a biphasic response (an initial increase followed by a decrease in the IASP). β-Adrenoceptor antagonist propranolol had no significant effect on the increase in the IASP by HGNS but almost abolished the decrease in the IASP caused by HGNS and unmasked the excitatory responses. The IAS responses to HGNS were frequency dependent and abolished by guanethidine (adrenergic blocker). l-NNA caused significant and stereoselective suppression of all IAS responses to HGNS. The suppressed HGNS responses were completely reversed by the NO precursor l-arginine stereoselectively. The NO synthase inhibitor and guanethidine had no effect on the increase in IASP by phenylephrine. Conclusions: NO may play a significant role in the facilitatory modulation of sympathetic responses in the IAS. © 1993.