Increasing antidumping effect of intestinal pacing with motor-active agents

Systematic review of small intestine pacing parameters for modulation of gut function

BACKGROUND AND PURPOSE

The efficacy of conventional treatments for severe and chronic functional motility disorders remains limited. High-energy pacing is a promising alternative therapy for patients that fail conventional treatment. Pacing primarily regulates gut motility by modulating rhythmic bio-electrical events called slow waves. While the efficacy of this technique has been widely investigated on the stomach, its application in the small intestine is less developed. This systematic review was undertaken to summarize the status of small intestinal pacing and evaluate its efficacy in modulating bowel function through preclinical research studies.

METHODS

The literature was searched using Scopus, PubMed, Ovid, Cochrane, CINAHL, and Google Scholar. Studies investigating electrophysiological, motility, and/or nutrient absorption responses to pacing were included. A critical review of all included studies was conducted comparing study outcomes against experimental protocols.

RESULTS

The inclusion criteria were met by 34 publications. A range of pacing parameters including amplitude, pulse width, pacing direction, and its application to broad regional small intestinal segments were identified and assessed. Out of the 34 studies surveyed, 20/23 studies successfully achieved slow-wave entrainment, 9/11 studies enhanced nutrient absorption and 21/27 studies modulated motility with pacing.

CONCLUSION

Small intestine pacing shows therapeutic potential in treating disorders such as short bowel syndrome and obesity. This systematic review proposes standardized protocols to maximize research outcomes and thereby translate to human studies for clinical validation. The use of novel techniques such as high-resolution electrical, manometric, and optical mapping in future studies will enable a mechanistic understanding of pacing.

Diffused and sustained inhibitory effects of intestinal electrical stimulation on intestinal motility mediated via sympathetic pathway

OBJECTIVE

The aims were to investigate the energy-dose response effect of intestinal electrical stimulation (IES) on small bowel motility, to compare the effect of forward and backward IES, and to explore the possibility of using intermittent IES and mechanism of IES on intestinal motility.

MATERIALS AND METHODS

Five dogs implanted with a duodenal cannula and one pair of intestinal serosal electrodes were studied in five sessions: 1) energy-dose response study; 2) forward IES; 3) backward IES; 4) intermittent IES vs. continuous IES; 5) administration of guanethidine. The contractile activity and tonic pressure of the small intestine were recorded. The duration of sustained effect after turning off IES was manually calculated.

RESULTS

1) IES with long pulse energy dose dependently inhibited contractile activity and tonic pressure of the small intestine (p < 0.001). 2) The duration of sustained inhibitory effect of IES on the small intestine depended on the energy of IES delivered (p < 0.001). 3) The potency of the inhibitory effect was the same between forward and backward IES. 4) The efficacy of intermittent IES was the same as continuous IES in inhibiting motility of the small intestine. 5) Guanethidine blocked the inhibitory effect of IES on intestinal motility.

CONCLUSIONS

IES with long pulses inhibits small intestinal motility; the effect is energy-dose dependent, diffused, and sustained. Intermittent IES has the same efficacy as the continuous IES in inhibiting small intestinal motility. Forward and backward IES have similar inhibitory effects on small bowel motility. This IES-induced inhibitory effect is mediated via the sympathetic pathway.

Electroacupuncture improves rectal distension-induced delay in solid gastric emptying in dogs

The aim of this study was to investigate the effects and mechanisms of electroacupuncture (EA) on rectal distension (RD)-induced delay in solid gastric emptying in dogs. Gastric emptying of solids was assessed in 12 dogs chronically implanted with a duodenal cannula by collecting samples at different time points from the cannula and measuring the dried weights of the samples. Bethanechol and atropine were used to qualitatively validate the method. In separate experiments, gastric emptying of solids was measured in a number of sessions: control, RD, RD + sham-EA, RD + EA of 6 mA, RD + EA of 3 mA, and RD + EA + naloxone. The method of gastric emptying by collecting and drying gastric chyme from the duodenal cannula was found to be accurate and reliable. Using the method, we found gastric emptying to be accelerated with bethanechol (70.01 ± 8.10% vs. 82.61 ± 4.15%, P = 0.04, vs. control) and delayed with atropine (4.31 ± 1.57%, P < 0.001, vs. control). RD substantially and significantly delayed gastric emptying. EA, but not sham-EA, attenuated delayed gastric emptying induced by RD (sham-EA: 48.79 ± 9.47% vs. EA: 74.28 ± 5.96%, P < 0.01). The effect was more potent with EA of 6 mA than EA of 3 mA and blocked by naloxone. EA is able to attenuate RD-induced delay in gastric emptying of solids, and this ameliorating effect may be mediated via the opioid pathway. EA may have a therapeutic potential for treating delayed gastric emptying attributed to lower gut distension.

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.

Intestinal electrical stimulation improves delayed gastric emptying and vomiting induced by duodenal distension in dogs

The aim of this study was to investigate the effects of short-pulse intestinal electrical stimulation (IES) on duodenal distention-induced delayed gastric emptying and vomiting in dogs and its possible mechanisms. The study was performed in 12 dogs with jejunal electrodes and a duodenal cannula in three separate experiments to investigate the effects of IES on duodenal distension (DD)-induced delayed gastric emptying and discomfort signs, vagal efferent activity, and jejunal tone. We found that: (i) IES significantly accelerated gastric emptying of liquid delayed by distension (18.05 +/- 4.06%vs. 7.18 +/- 1.99%, P = 0.036 at 60 min). (ii) IES significantly reduced vomiting and discomfort/pain induced by distension. The average signs score was 15.33 +/- 1.37 during distension which decreased to 6.50 +/- 0.91 (P = 0.0002) with IES. (iii) IES did not change vagal afferent activity, which was assessed by the spectral analysis of the heart rate variability. (iv) IES decreased jejunal tone. In conclusion, IES with parameters commonly used in gastric electrical stimulation for nausea and vomiting associated with gastroparesis improves DD-induced delayed gastric emptying and prevents DD-induced vomiting and discomfort signs. Further studies are warranted to investigate the therapeutic potential of IES for gastrointestinal symptoms associated with disturbances in motility and sensory function in small intestine.

Gastrointestinal electrical stimulation for treatment of gastrointestinal disorders: gastroparesis, obesity, fecal incontinence, and constipation

Electrical stimulation of the gastrointestinal (GI) tract is an attractive concept. Since these organs have their own natural pacemakers, the electrical signals they generate can be altered by externally delivering electric currents by intramuscular, serosal, or intraluminal electrodes to specific sites in the GI tract. This article reviews the advances in electrical stimulation of the GI tract by describing various methods of GI electrical stimulation and their peripheral and central effects and mechanisms; updating the status of GI electrical stimulation in the clinical settings of gastroparesis, obesity, fecal incontinence, and constipation; and predicting future directions and developments of GI electrical stimulation technology and their areas of possible clinical applications.

Neural mechanisms involved in the inhibition of intestinal motility induced by intestinal electrical stimulation in conscious dogs

The effects and mechanisms of intestinal electrical stimulation (IES) with long pulses on intestinal motility were investigated in conscious dogs. Eighteen dogs were equipped with serosal electrodes and an intestinal cannula in the small bowel. The first experiment was designed to study the effect of one-channel IES on intestinal motility and the extent of this effect. The second experiment was conducted to study the effect of IES on intestinal motility and the involvement of neural pathway. The IES with long pulses significantly inhibited intestinal motility. Intestinal motility of the entire measured segment (40-220 cm distal to the stimulation electrodes) was inhibited by 60-74% with the single-channel IES with long pulses. Hexamethonium, guanethidine, phentolamine, propranolol partially, but not N(omega)-nitro-L-arginine (L-NNA), ondansetron and naloxone prevented the inhibitory effect of IES on intestinal motility. We conclude that single-channel IES inhibits intestinal motility within a distance of at least 2 m. This inhibitory effect induced by IES with long pulses is mediated via sympathetic but not nitrergic, serotoninergic 5-HT(3) and opiate pathway.

Gastrointestinal pacing

Gastrointestinal pacing has been used to alter motor function and is effective in animal models in modulating gastric emptying, intestinal transit, and absorption. Application of gastrointestinal pacing to disorders of the human stomach and small bowel is an attractive treatment option that may some day become a clinical reality. Several technical problems must be overcome before further clinical testing can proceed.

[Electrostimulation of ileum and jejunum reservoirs in an acute and chronic experiment]

Voluntary control of the motility of intestinal reservoirs may be used to improve evacuation and continence. In 4 dogs a U-shaped jejunum pouch and in another 4 an ileum pouch was constructed and instrumented with stimulating and EMG electrodes and pressure lines. In the acute experiments jejunum pouch stimulation with 200 microseconds 1.67 kHz 30 mA increased the intrapouch pressure by 38 +/- 4 mm Hg (n = 6) and 500 microseconds 910 Hz 25 mA by 60 +/- 5 mm Hg (n = 3). The pressure increase in the awake animals was consistently lower (200 microseconds 4 +/- 6 mm Hg, n = 9; 500 microseconds 25 +/- 17, n = 11). The ileum pouch responded with a 37 +/- 10 mm Hg pressure increase (n = 9) to 50 ms 6 Hz 20 mA pulse trains. Ileum pouches could not be stimulated in the awake animal due to contraction of the abdominal wall. Electrostimulation may be used to contract and evacuate intestinal reservoirs but additional drug therapy or autonomic nerve stimulation will be necessary to lower the thresholds especially for ileum stimulation in the awake animal.