Acid challenge delays gastric pressure adaptation, blocks gastric emptying and stimulates gastric fluid secretion in the rat

Functional dyspepsia can be associated with impaired gastric relaxation in response to food intake and delayed gastric emptying. In this study, we investigated whether luminal hydrochloric acid (HCl) may reproduce these motor alterations in phenobarbital‐anaesthetized rats via activation of extrinsic neural pathways. Intragastric pressure (IGP) changes induced by a 2‐mL fluid bolus were recorded with an oesophageal catheter, and gastric emptying was determined via the fluid volume recovered from the stomach 30‐min post‐bolus. Experiments involving acute nerve transections or pharmacological blockade of nitric oxide synthesis revealed that the initial increase of IGP after a 0.35 mol L−1 HCl bolus is dampened by duodenogastric and gastrogastric relaxation reflexes depending on vagal and splanchnic pathways as well as nitric oxide. Compared with saline, HCl (0.15–0.5 mol L−1) delayed the subsequent decrease (adaptation) of IGP, inhibited gastric emptying and stimulated gastric fluid secretion as seen in stomachs with ligated pylorus. The acid‐evoked delay in IGP adaptation and inhibition of gastric emptying involved duodenogastric and duodenopyloric extrinsic nerve reflexes, whereas the gastric fluid secretion was independent of the extrinsic innervation. It is proposed that the gastropyloric motor changes induced by luminal acid challenge have a bearing on the motor disturbances underlying functional dyspepsia.