Ectopic jejunal pacemakers after jejunal transection and their relationship to transit

The hypothesis was that orally moving pacesetter potentials distal to a site of jejunal transection and anastomosis would slow transit through jejunum containing them and that reoperation with excision of bowel containing these pacesetter potentials would restore transit to the control. In six conscious dogs with jejunal serosal electrodes for recording myoelectric activity and a jejunal perfusion/aspiration catheter for measuring transit, jejunal pacesetter potential frequency decreased distal to a midjejunal transection and anastomosis from 18.7 +/- 0.3 (SE) cycles/min (cpm) proximal to the site to 14.4 +/- 0.6 cpm distal to the site (P < 0.05). In addition, orally propagating pacesetter potentials occurred > 25% of the time in a 37 +/- 7 cm length of bowel distal to the site during fasting and after feeding. Transit through the segment with the orally moving pacesetter potentials was slowed during feeding (half time before and after transection, 7.7 +/- 1.1 and 13 +/- 2.0 min, respectively, P < 0.05). Resection of the segment with the abnormal pacesetter potentials shortened the length of bowel containing them to 24 +/- 2 cm (P > 0.05) and restored transit to the control. In conclusion, orally moving pacesetter potentials distal to a canine jejunal transection and anastomosis slowed transit through the segment of bowel containing them. Resection of the segment restored transit to the control.

Transcutaneous electrovesicography

Transcutaneous electrovesicography was performed in 22 healthy volunteers (mean age 41.6 years, 12 men and 10 women) with the urinary bladder (UB) both full and empty. The study was performed also in 9 cystectomy patients who had had bladder cancer (mean age 37.6 years, 6 men and 3 women). Optimal electrode position was established by locating one electrode above and lateral to each pubic tubercle and a 3rd one above the symphysis pubis. A reference electrode was applied to a lower limb. A strain gauge respiratory transducer was attached to the thoracic wall. Pacesetter potentials (PPs) were recorded from both the full and empty UB. The PPs were triphasic and had the same frequency, amplitude and regular rhythm when repeated in the individuai subject. PPs recorded from the empty UB had the same character but a lower amplitude than those recorded from the full UB. Ali of the cystectomy patients had a ‘silent’ electrovesicogram. In conclusion, electrovesicography could be performed transcutaneously. It may be a useful investigative method in the diagnosis of vesical disorders. It is safe, simple, without complications and cost-effective.

Relaxation oscillator and core conductor models are needed for understanding of GI electrical activities

This review examines the applicability of modeling of intestinal electrical activities (slow waves or pacesetter potentials) by coupled relaxation oscillator models, in comparison to a “multidimensional model” based on core conductor theory. We briefly review the relaxation oscillator model and correct some misunderstandings. We point out that new insights about the role of networks of interstitial cells of Cajal in intestinal pacemaking require reconsideration of the mechanisms producing oscillations, the coupling between oscillators, and how the oscillator network is coupled to the driven cells. Recent advances in relaxation oscillator models allow the production of pacemaking pacemaking activity, which can be selectively varied as to waveform, frequency, and occurrence of silent periods. Core conductor models do not produce pacemaking activity or permit this flexibility. We point out that many of the criticisms leveled against relaxation oscillator models relate to studies made in simplified in vitro systems constrained by extensive dissection. Such systems do not adequately reflect the in vivo systems. We conclude that a full understanding of control of electrical (and mechanical) events in the gastrointestinal tract requires that better understanding of relaxation oscillator models growing out of recent research be combined with improved applications of core conductor theory to multidimensional models.

Effects of gastric pacing on canine gastric motility and emptying

Gastric pacing has been achieved in dogs and humans, but its effects on gastric motility and emptying have not been thoroughly explored. Seven dogs had bipolar electrodes placed 1 and 10 cm proximal to the pylorus for reverse and forward pacing and monopolar recording electrodes and strain gauges placed 3, 5, and 7 cm proximal to the pylorus. After recovery, myoelectrical and contractile activity and gastric emptying of a mixed meal (50 g 99mTc-labeled liver and 250 ml 111In-labeled 5% dextrose broth solution) were measured in each of three conditions: no pacing, reverse pacing, and forward pacing (frequency 0.5 cycles/min above intrinsic pacesetter potential frequency). Reverse pacing reversed the direction of > 90% of antral pacesetter potentials and peristaltic waves in six of seven dogs, prolonged the lag phase of solid emptying, prolonged the half emptying time of solids and liquids, and increased the antral motility index. Forward pacing entrained pacesetter potentials but had no consistent effect on emptying or antral contractions. In conclusion, reverse gastric pacing slows gastric emptying of digestible solids and liquids by reversing the direction of antral peristalsis and increasing the antral motility index, whereas forward pacing has no such effects.

Regulation of canine jejunal transit

The aim of this study was to determine what factors influence the direction of movement of canine jejunal chyme. In four dogs, pacing electrodes were implanted near each end of a 50-cm jejunal Vella loop, while recording electrodes and intraluminal pressure catheters were spaced along the loop. After recovery, the loop was perfused from either the proximal stoma (forward flow) or the distal stoma (reversed flow), and effluent was collected from the nonperfused stoma. The pacesetter potentials were paced electrically in a forward (aborad) or a reverse (orad) direction. During control conditions (forward flow-forward pacing), the mean transit time of liquids was 2.6 +/- 0.1 min (mean +/- SE) and the static volume of the loop was 8.8 +/- 0.3 ml. Reversing both direction of flow and direction of pacesetter potential propagation slowed transit (4.4 +/- 0.4 min; P less than 0.05) and increased loop volume (16.0 +/- 1.0 ml; P less than 0.01). Reversing flow with forward pacing resulted in even slower transit (7.5 +/- 1.2 min; P less than 0.05), maintained a large volume (33 +/- 10 ml), and increased basal pressure in the loop from -1.2 +/- 1.7 (control) to 2.3 +/- 1.6 mmHg (P less than 0.05). These observations suggest that the direction of propagation of jejunal pacesetter potentials influences the direction of movement of jejunal chyme but that other factors have a role as well.

Mechanisms of enhanced canine enteric absorption with intestinal pacing

Electrical pacing enhances absorption from the canine small bowel, but the mechanism of this effect is unknown. To explore the mechanism, conscious dogs with two Vella loops, a proximal jejunal and a distal ileal, each 50 cm long, were studied. Pacing the jejunal loop with 15–18 pulses/min entrained the pacesetter potentials of the jejunal loop and increased water, sodium, and glucose absorption from the jejunal loop. Jejunal pacing also increased water absorption from the unpaced, ileal loop. Conversely, ileal pacing did not entrain the ileal loop or enhance absorption from the ileal loop. However, it did enhance water absorption in the unpaced jejunal loop. After alpha-blockade with phentolamine or celiac and superior mesenteric ganglionectomy, jejunal pacing did not increase jejunal or ileal absorption. In contrast, after beta-blockade with propranolol, pacing still enhanced jejunal absorption in three out of four dogs. Vagotomy alone enhanced jejunal but not ileal absorption, but the enhancement was not further increased by pacing. In conclusion, electrical pacing of the small bowel elicited a local and distant increase in net water absorption; the effect was mediated in part by an alpha-adrenergic mechanism.

Stimulation of motilin release by bombesin in dogs

Bombesin (BBS) was infused in conscious fasting dogs to document its effects on the release of motilin in the blood and on intestinal motility. When BBS was infused for 3 h (0.125 and 0.5 microgram X kg-1 X h-1), a specific pattern of myoelectric activity was induced: 1) the pacesetter potentials were increased in frequency but decreased in amplitude; 2) a moderate spike activity (weak phase II) was superimposed on this disorganized pacesetter activity, and activity fronts were abolished despite elevated motilin levels. A second experiment was performed in which motilin levels during BBS administration for a selected period of an interdigestive myoelectric complex (IDMC) could be compared with those obtained at a similar period of a preceding IDMC in which a saline solution had been infused. The motilin blood levels measured during BBS administration (0.25, 0.5, 1.0, and 2.0 micrograms X kg-1 X h-1 for 20 min each stepwise) were significantly higher than those obtained with saline. The administration of BBS synchronized with the IDMC was necessary to document its effect on motilin release, because when BBS was infused at an unknown period of the IDMC no rise of motilin levels over basal could be detected. Because of its contradictory effects on the release of motilin (stimulation of motilin release) and on the IDMC (inhibition of motilin effect), a physiological role of BBS as an endocrine regulator of motilin release is questionable. On the other hand, the possibility that BBS controls motilin release in a paracrine or neurocrine role cannot be excluded.

Electrical control of canine jejunal propulsion

We wondered whether the direction of propagation of intestinal pacesetter potentials determines the direction of movement of intestinal content. In six dogs, electrodes for pacing were implanted near each end of an 80-cm isolated jejunal loop, and a cannula was positioned at the middle of the loop for intraluminal insertion of solids and/or liquids. After recovery and during fasting, 50 nylon spheres (2 mm diam) always emptied from the distal stoma regardless of the direction of pacing. In contrast, 150 mM NaCl, given alone at 2.8 ml/min or with spheres, emptied from the distal stoma during forward pacing and from the proximal stoma during backward pacing. Spheres given with the liquid emptied from the distal stoma during forward pacing, but during backward pacing, the site of emptying varied among dogs. Neither pacing nor spheres altered jejunal interdigestive myoelectric cycles, but the perfusate abolished the cycles and resulted in a noncyclic pattern of jejunal action potentials. We concluded that the direction of pacesetter potential propagation determined the direction of liquid transit. Direction of solid transit depended, in part, on other mechanisms.

Patterns of gastric electrical and motor activity in miniature pigs

Gastric myoelectrical and mechanical activity was recorded in miniature pigs using chronically implanted electrodes and strain gauge force transducers. Semiautomated methods were devised to obtain quantitative evaluations of the electrical and mechanical parameters measured in fasted and fed animals. The patterns of gastric myoelectrical activity in pigs were, on the whole, similar to the patterns described in dogs, including regular cyclic control activity and spike response activity associated with muscle contraction. However, several points were peculiar to the species studied: conduction velocity of pacesetter potentials increased only moderately in the antrum; tachygastria never occurred in the experiments; in response to a standard meal, the frequency of pacesetter potentials gradually increased; mechanical activity proceeded at its maximal force immediately after feeding and for a long period; no evidence of 'migrating electrical complexes' was found in the stomach during fasting. The 40-min period following administration of a test meal appeared especially suitable for pharmacological or physiological experiments in which inhibitory factors are to be tested on the stomach.