HTR4 and gastroesophageal reflux disease: For example, tegaserod, a partial 5-HT4R agonist, can safely and effectively reduce postprandial esophageal acid exposure by enhancing the esophageal acid clearance capacity, accelerating gastric emptying, and reducing the occurrence of transit lower esophageal sphincter relaxation (TLESR) [15], promoting bicarbonate and mucus secretion from the SMGs [13] and adjusting visceral sensitivity, thus reducing reflux, lowering the pain threshold of the esophagus to mechanical expansion, improving esophageal peristalsis, and reducing functional heartburn symptoms [14,16,17].