Facilitation of gastric compliance and cardiovascular reaction by repeated isobaric distension of the rat stomach
Gastric distension causes cardiovascular reactions and enhances gastric compliance. Here we investigated how these responses are related to each other, whether they change upon repeated distension and which neural mechanisms are involved. Mean arterial blood pressure (MAP) in phenobarbital-anaesthetized rats was recorded from a carotid artery and gastric compliance determined with an electronic barostat. Runs of intermittent gastric distension were generated by stepwise increments (5 mm Hg) of intragastric pressure. While gastric compliance peaked at intragastric pressures of 20 mm Hg, the change in MAP (predominantly hypotension) was largest at intragastric pressures beyond 30 mm Hg. Repeated distension enhanced the MAP response to intragastric pressures beyond 35 mm Hg, whereas gastric compliance was facilitated primarily at intragastric pressures below 20 mm Hg. This facilitation of gastric compliance depended on the magnitude of the preceding distension. The MAP response to distension was enhanced by nitric oxide synthase inhibition, inhibited by subdiaphragmatic vagotomy but hardly affected by coeliac ganglionectomy. The facilitation of gastric compliance was changed by vagotomy in a complex manner but left unaltered by the other interventions. These findings show that isobaric gastric distension elicits both MAP and gastric compliance responses whose characteristics, mechanisms and sensitization properties differ profoundly.