8 The effect of food on electrical and mechanical activity of the canine antrum.

Background: Gastric electrical and mechanical activities are modulated by food, however, the pattern of food-induced changes and the mechanisms governing them are not well defined. Aim: To characterize food–induced changes in gastric antral activity and to explore underlying mechanisms for such changes. Methods: Experiment 1- intended to test the effect of food on gastric signals. Two bipolar electrodes were implanted in the antrum of 7 mongrel dogs for simultaneous recording of slow wave rate, in events /min (SWR), and contractions assessed by electrical impedance (AI) in ohms. A strain-gauge transducer was implanted in 3 dogs to correlate changes in AI with contractions. The meal consisted of a preload of 100 g of dry food followed in 10 min, by 900 g of the same food, to lengthen meal duration. SWR and AI were determined during 4 periods of 5 min/each (baseline, end of preload, satiety, 10 min after satiety). Experiment was repeated 5 times/dog. Experiment 2-acute study, under anesthesia with 3 tests: 1) esophageal balloon distension 2) fundic balloon distension at volumes of 50–400 ml, using a balloon of 800 ml, and 3) nitroglycerin infusion, 0.5 (g kg^­1 min^­1 for 10 min. results as Mean ± SD. Results: Experiment 1- frequency of antral contractions by strain-gauge correlated well with frequency of contractions as measured by AI, R = 0.76. SWRs at baseline, preload, satiety and post satiety were: 5.0 ± 0.3, 4.9 ± 0.4, 3.8 ± 0.65, and 4.4 ± 0.47 respectively. SW amplitudes (ohms) at the same periods were: 5.3 ± 1.4, 8.5 ± 2.1, 12.2 ± 4.3 and 12.0 ± 5.3 respectively; p < 0.05 for satiety and post satiety vs. baseline for both measurements. Both changes peaked around the time of satiety. Mean time interval between satiety and slowest SWR was 80 ± 40 sec. Amplitude of contractions remained elevated for 212 ± 110 min after the meal. Experiment 2- fundic distension caused a transient decrease in SWR at lower volumes, but the decrease was sustained at the 400 ml volume, 3.9 ± 0.2 vs. 3 ± 0.8, baseline vs. distension, respectively, p = 0.002. NTG significantly reduced SWR: 4.0 ± 0.7 vs. 3.5 + 0.8, baseline vs. infusion, p = 0.007. Esophageal distension did not affect SWR. Conclusions: Food ingestion causes a significant decrease in SWR and significant enhancement of antral contractions that peak at satiety. This suggests a possible causal relationship that can be potentially useful when considering gastric electrical stimulation for modulation of satiety signals. Both gastric distension and nitrergic pathways affect SWR. [ABSTRACT FROM AUTHOR]