The viscerovisceral reflex control of gastric tone remains poorly characterized. We have previously demonstrated physiological variations in gastric tone that occur during fasting and after feeding. These variations are neurally regulated. We have now compared the reflex mechanisms modulating gastric tone that are elicited by esophageal or duodenal distension in fasted, conscious dogs. To determine the pathways involved in these reflexes, we combined the technique of vagal blockade (by cooling the supradiaphragmatic vagi isolated within a surgically implanted cooling jacket) with the administration of autonomic drugs. Gastric tone was measured as the air volume within an intragastric bag maintained at a constant, low pressure by an electronic barostat. Standardized distensions were performed by means of an inflatable balloon-catheter positioned either in the mid-esophagus (in three dogs) or in the distal duodenum (in three dogs). A profound and consistent gastric relaxation was induced by distension of either the esophagus (247 +/- 21 ml delta volume, P less than 0.05) or the duodenum (238 +/- 29 ml, P less than 0.05). Supradiaphragmatic vagal cooling abolished the gastric relaxatory response to duodenal distension and significantly reduced, but did not completely suppress, the response to esophageal distension. Neither cholinergic stimulation (intravenous bethanechol) nor adrenergic blockade (combined intravenous phentolamine and propranolol) had any significant effect on either gastric relaxatory response. Combined adrenergic and cholinergic (intravenous atropine) blockade induced gastric relaxation, but failed to suppress the gastric responses. We conclude that both esophageal and duodenal distension elicit gastric relaxation by a noncholinergic vagal mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)