In the present study we have examined the hypothesis that transient lower esophageal sphincter relaxations are under vagal control. Fasting esophageal motor function was monitored with a manometric sleeve catheter passed via a cervical esophagostomy. Gastric insufflation with oxygen resulted in intermittent venting of gas into the esophagus during transient lower esophageal sphincter relaxations. Such venting of gas was associated with the occurrence of esophageal body common cavities and gas venting from the esophageal stoma, all of which increased with increasing rates of gastric insufflation. The optimal insufflation rate, 80 ml/min, produced stomal gas venting at a rate of 10.3 +/- 1.1/h (mean +/- SE). The time and pressure profiles of transient lower esophageal sphincter relaxations induced by gastric insufflation were similar to those relaxations seen with spontaneous postprandial gastroesophageal reflux and belching in dogs. Sphincteric relaxation started 10 s before the onset of common cavities. In all 4 dogs, cooling of cervical subcutaneous vagosympathetic loops abolished transient lower esophageal sphincter relaxations, common cavities, and stomal gas venting. Within 1-4 min of cessation of vagal cooling, all three markers of gastroesophageal gas venting returned. Atropine, 50 and 200 micrograms/kg i.v., did not block transient lower esophageal sphincter relaxations or gas reflux. Gastric gaseous distention is a potent and consistent trigger of transient lower esophageal sphincter relaxations in the dog. This effect can be used as a model for study of control mechanisms of transient sphincter relaxation-dependent gastroesophageal reflux. Our observations with this model indicate that transient lower esophageal sphincter relaxations are under vagosympathetic control, but that muscarinic mechanisms are not important mediators of this control.