Regulation of Contractile Activity of the Lower Esophageal Sphincter in Rats by Serotonin

Serotonin (5-hydroxytryptamine, 5-HT) can stimulate the lower esophageal sphincter (LES) by indirect actions on the modulation of reflexes and by a direct action on smooth muscles. Aim:of this study was to investigate the role of 5-HT and selective 5-HT receptor subtypes in the regulation of the lower esophageal sphincter (LES) in the rat by measuring electromotor activity of the LES. Methods:The i.v. administration of 5-HT was carried out, and the LES contractile activity was evaluated by measuring the amplitude and frequency of the slow waveand spikes of electromyogram (EMG). Electromyography is the technique that uses surface microelectrodes (placed on the skin)near the border between the esophagus and cardia of the stomach. Results: Serotonin administration increased the frequency and the amplitude of the EMG ofthe LES. Selective pharmacological inhibition of separate serotonin 5-HT1-, 5-HT2-, 5-HT3-, and 5-HT4-receptors not completely rule outthe serotonin induced increment of EMG activity of theLES .Joint pharmacological inhibition of thepair of 5-HT1and 5-HT2 receptors completely–but the pair of 5-HT3and 5-HT4 receptors only partially inhibited the serotonin induced increment of EMG activity of the LES . Conclusion:These data suggest that serotonin enhancement of the LES contractile activity is mediated by activation of 5-HT1,2, 3, and 4 receptor subtypes. The serotonin induced increment of EMG activity of the LES more fully realized by the pair of effector 5-HT1and 5-HT2-receptors than by the pair of ganglionary5-HT3and 5-HT4 receptors.