Three Gaseous Neurotransmitters, Nitric oxide, Carbon Monoxide, and Hydrogen Sulfide, Are Involved in the Neurogenic Relaxation Responses of the Porcine Internal Anal Sphincter

BACKGROUND/AIMS: The internal anal sphincter (IAS) plays an important role in maintaining continence and a number of neurotransmitters are known to regulate IAS tone. The aim of this study was to determine the relative importance of the neurotransmitters involved in the relaxant and contractile responses of the porcine IAS. METHODS: Responses of isolated strips of IAS to electrical field stimulation (EFS) were obtained in the absence and presence of inhibitors of neurotransmitter systems. RESULTS: Contractile responses of the sphincter to EFS were unaffected by the muscarinic receptor antagonist, atropine (1 muM), but were almost completely abolished by the adrenergic neuron blocker guanethidine (10 muM). Contractile responses were also reduced (by 45% at 5 Hz, P carbon monoxide > hydrogen sulfide.