Inhibitory effects and mechanisms of intestinal electrical stimulation on gastric tone, antral contractions, pyloric tone, and gastric emptying in dogs

The aim of this study was to investigate the effects and mechanisms of intestinal electrical stimulation (IES) on gastric tone, antral and pyloric contractions, and gastric emptying in dogs. Female hound dogs were equipped with a duodenal or gastric cannula, and one pair of serosal electrodes was implanted in the small intestine. The study consisted of five different experiments. Liquid gastric emptying was assessed by collection of chyme from the duodenal cannula in a number of sessions with and without IES and with and without N-nitro-l-arginine (l-NNA). Postprandial antral and pyloric contractions were measured with and without IES and in the absence and presence of l-NNA or phentolamine by placement of a manometric catheter into the antrum and pylorus via the duodenal cannula. Gastric tone was assessed by measurement of gastric volume at a constant pressure. Gastric emptying was substantially and significantly delayed by IES or l-NNA compared with the control session. IES-induced delay of gastric emptying became normal with addition of l-NNA. IES reduced gastric tone, which was blocked by l-NNA. IES also inhibited antral contractions (frequency and amplitude), and this inhibitory effect was not blocked by l-NNA but was blocked by phentolamine. IES alone did not affect pyloric tone or resistance, but IES + l-NNA decreased pyloric tone. In conclusion, IES reduces gastric tone via the nitrergic pathway, inhibits antral contractions via the adrenergic pathway, does not affect pyloric tone, and delays liquid gastric emptying. IES-induced delay of gastric emptying is attributed to its inhibitory effects on gastric motility.

Effects of duodenal distension on antropyloroduodenal pressures and perception are modified by hyperglycemia

Marked hyperglycemia (blood glucose ∼15 mmol/l) affects gastrointestinal motor function and modulates the perception of gastrointestinal sensations. The aims of this study were to evaluate the effects of mild hyperglycemia on the perception of, and motor responses to, duodenal distension. Paired studies were done in nine healthy volunteers, during euglycemia (∼4 mmol/l) and mild hyperglycemia (∼10 mmol/l), in randomized order, using a crossover design. Antropyloroduodenal pressures were recorded with a manometric, sleeve-side hole assembly, and proximal duodenal distensions were performed with a flaccid bag. Intrabag volumes were increased at 4-ml increments from 12 to 48 ml, each distension lasting for 2.5 min and separated by 10 min. Perception of the distensions and sensations of fullness, nausea, and hunger were evaluated. Perceptions of distension ( P < 0.001) and fullness ( P < 0.05) were greater and hunger less ( P < 0.001) during hyperglycemia compared with euglycemia. Proximal duodenal distension stimulated pyloric tone ( P < 0.01), isolated pyloric pressure waves ( P < 0.01), and duodenal pressure waves ( P< 0.01). Compared with euglycemia, hyperglycemia was associated with increases in pyloric tone ( P < 0.001), the frequency ( P < 0.05) and amplitude ( P < 0.01) of isolated pyloric pressure waves, and the frequency of duodenal pressure waves ( P < 0.001) in response to duodenal distension. Duodenal compliance was less ( P < 0.05) during hyperglycemia compared with euglycemia, but this did not account for the effects of hyperglycemia on perception. We conclude that both the perception of, and stimulation of pyloric and duodenal pressures by, duodenal distension are increased by mild hyperglycemia. These observations are consistent with the concept that the blood glucose concentration plays a role in the regulation of gastrointestinal motility and sensation.

Effects of intraduodenal glucose infusion on gastric myoelectrical activity and antropyloroduodenal motility

Intraduodenal nutrient infusions cause an inhibition of antral motility and an increase in pyloric motility. The involvement of gastric myoelectrical activity in this intestinogastric feedback was studied. Electrogastrography and antropyloroduodenal manometry were performed in 10 healthy volunteers. The effects of 20-min infusions of 25% glucose (4 kcal/min) and saline were compared. Intraduodenal glucose infusions caused a decrease in the power of the dominant frequency in the electrogastrogram ( P = 0.028), but the frequency itself remained unchanged. The total number of dysrhythmias increased ( P = 0.035). An inhibition of antral motor activity ( P = 0.001), an increase in the number of isolated pyloric pressure waves ( P = 0.027), and an increase in basal pyloric tone ( P = 0.001) were simultaneously recorded. The change in power during glucose infusion correlated positively with the change in the antral motility index ( rs= 0.50, P = 0.001). It is concluded that inhibition of gastric myoelectrical activity is one of the mechanisms underlying an inhibition of motor activity in the gastric antrum.

Topography and measurement of pyloric pressure waves and tone in humans

The topography of human pyloric pressure is ill defined, and previous studies of pyloric motility in humans have given conflicting results. A detailed profile of pyloric pressure has been recorded in seven healthy volunteers using a manometric assembly with 13 side holes spaced at 3-mm intervals on reverse aspect of a 3.5-cm long sleeve sensor. After a fasting control period of 40 min, recordings were made for 40 min during intraduodenal infusion of a lipid emulsion. Two major patterns of pressure waves were seen during the fasting control period, namely pressure waves confined to a narrow pyloric zone (isolated pyloric pressure waves) and pressure waves that were less localized and involved the antrum and/or duodenum. During lipid infusion the motility pattern was dominated by isolated pyloric pressure waves and localized pyloric tone. Ninety-two percent of the isolated pyloric pressure waves recorded by the sleeve were recorded by only one or two side holes, consistent with a phasically active zone less than 9 mm in length. Pyloric tone was confined to an even narrower zone and was most often recorded by only one side hole. When both tone and isolated pyloric pressure waves occurred together, they were recorded by the same side holes. By comparison with the side holes, the sleeve recorded 89% of isolated pyloric pressure waves and 98% of nonlocalized waves and recorded pyloric tone with a moderate sensitivity but high specificity. The technical challenge of recording localized pyloric contraction is considerable, and much of the conflict between previous studies of the human pylorus is explicable on methodological grounds.(ABSTRACT TRUNCATED AT 250 WORDS)

Antropyloroduodenal motor responses to intraduodenal lipid infusion in healthy volunteers

The delivery of lipid to the duodenum has been shown to slow gastric emptying and to increase the resistance to gastric outflow. To investigate mechanisms responsible for these effects, we have recorded antropyloroduodenal motility in nine healthy volunteers during alternate intraduodenal infusions of normal saline and triglyceride emulsion (Intralipid 10%). During the lipid infusions there were reproducible, major changes in the patterns of motility. Pressure waves, apparently isolated to the pylorus, usually started within 10 min of initiation of the lipid infusion. After 20-25 min of lipid infusion these waves occurred at median rates of 2.4 and 2.8/min (1st and 2nd lipid infusions, respectively); these rates were significantly greater (P less than 0.05) than the median rates (all less than or equal to 0.4/min) observed during the equivalent period of the succeeding saline infusions. During 10 of 22 lipid infusions, isolated pyloric pressure waves were associated with sustained pyloric tone. Infusion of lipid into the duodenum suppressed antral pressure waves in all subjects and initiated brief periods of regular duodenal contractions during 11 of 22 infusions. These studies have demonstrated alterations of antropyloroduodenal motor patterns in response to changes in the duodenal luminal content. The effects on antral and pyloric motility are probably of importance in the regulation of transpyloric flow by nutrients in the duodenal lumen.