[Gastrointestinal sphincters--pharmacologic viewpoints]

Bearing in mind the specificity of the functions of the gastrointestinal sphincters (GIS), we studied the responses of the lower esophageal sphincter (LES), the pyloric sphincter (PS), the ileocecal sphincter (ICS) and the internal anal sphincter (IAS) to noradrenaline (NA), acetylcholine (ACh), PGE1, PGF2 alpha and the peptide bombesin (B). The electrical and contractile activities as well as the response to field electrical stimulation (FES) were recorded. All sphincters except for PS responded to NA with depolarization and contractions. ACh at concentrations higher than 5 x 10(-6)M elicited a biphasic response from LES: depolarization followed by hyperpolarization and respectively contractions and relaxation. At concentrations higher than 10(-6)M ACh produced hyperpolarization and relaxation in IAS. Data were obtained about the modulating role of presynaptic N-cholinoreceptors in the release of a non-adrenergic, non-cholinergic (NANC) inhibitory neurotransmitter leading to hyperpolarization and relaxation in LES and IAS under the effect of exogenous ACh. PGE1 and PGF2 alpha increased the tone and decreased the FES-induced relaxation in LES. In PS PGE1 evoked relaxation and completely inhibited the response to FES. The pharmacological analysis showed that PGs modulated not only the adrenergic and cholinergic but also the NANC neurotransmission. Evidence is presented concerning the role of bombesin in the adrenergic, cholinergic, and NANC neurotransmission in LES.