Facilitation of gastric compliance and cardiovascular reaction by repeated isobaric distension of the rat stomach

Abstract

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 mmHg) of intragastric (IG) pressure. While gastric compliance peaked at IG pressures of 20 mmHg, the change in MAP (predominantly hypotension) was largest at IG pressures beyond 30 mmHg. Repeated distension enhanced the MAP response to IG pressures beyond 35 mmHg, whereas gastric compliance was facilitated primarily at IG pressures below 20 mmHg. 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.

Figure 1

Illustration of the intermittent gastric distension protocol (method of ascending limits) as delivered by the software Protocol Plus™. The intragastric pressure is increased by steps of 5 mm Hg, ranging from a minimal distending pressure of 5 mm Hg to a maximal pressure of 50 mm Hg. The distension steps last 30 s and are separated by periods of 3 min, during which the bag is deflated so that intragastric pressure returns to 0 mm Hg. The graph shows the recorded intragastric pressure (A), the recorded gastric volume (B) and the corrected gastric volume (C).

Figure 2

(A) Change in MAP and (B) gastric compliance during three runs of intermittent gastric distension from 5 to 50 mm Hg applied at inter-run intervals of 20 min. The values are means ± SEM; n = 6. * P < 0.05, ** P < 0.01 (run 3 vs. run 1); + P < 0.05, ++ P < 0.01 (run 2 vs. run 1).

Figure 3

Facilitation of gastric compliance on repeated gastric distension as expressed by the difference (D) in the gastric compliance at each step of distension runs 1 and 2. (A) Facilitation of gastric compliance induced by repeated distension runs from 5 to 20 mm Hg and 5 to 50 mm Hg applied at inter-run intervals of 20 min. (B) Facilitation of gastric compliance induced by repeated distension runs from 5 to 20 mm Hg applied at inter-run intervals of 20 min and 60 min. The values are means ± SEM; n = 6. * P < 0.05, ** P < 0.01 (vs. run from 5 to 20 mm Hg).

Figure 4

Effect of intravenous pretreatment with L-NAME on MAP and compliance during repeated gastric distension. (A) Change in MAP during the second run of intermittent gastric distension from 5 to 50 mm Hg. (B) Gastric compliance during the first run of intermittent gastric distension from 5 to 20 mm Hg. (C) Facilitation of gastric compliance on repeated gastric distension as expressed by the difference (D) in the gastric compliance at each step of distension runs 1 and 2 applied at an inter-run interval of 20 min. The animals were pretreated with vehicle (0.15 M NaCl, 1 ml/kg) or L-NAME (10 mg/kg) 25 min before application of run 1. The values are means ± SEM; n = 5. * P < 0.05 (vs. vehicle).

Figure 5

Effect of bilateral subdiaphragmatic vagotomy, relative to sham operation, on MAP and compliance during repeated gastric distension. (A) Change in MAP during the second run of intermittent gastric distension from 5 to 50 mm Hg. (B) Gastric compliance during the first run of intermittent gastric distension from 5 to 20 mm Hg. (C) Facilitation of gastric compliance on repeated gastric distension as expressed by the difference (D) in the gastric compliance at each step of distension runs 1 and 2 applied at an inter-run interval of 20 min. Vagotomy and sham operation were performed during setup of the animals for the experiments. The values are means ± SEM; n = 5. * P < 0.05 (vs. vehicle).

Figure 6

Effect of coeliac ganglionectomy, relative to sham operation, on MAP and compliance during repeated gastric distension. (A) Change in MAP during the second run of intermittent gastric distension from 5 to 50 mm Hg. (B) Gastric compliance during the first run of intermittent gastric distension from 5 to 20 mm Hg. (C) Facilitation of gastric compliance on repeated gastric distension as expressed by the difference (D) in the gastric compliance at each step of distension runs 1 and 2 applied at an inter-run interval of 20 min. Ganglionectomy and sham operation were performed during setup of the animals for the experiments. The values are means ± SEM; n = 5.