The effects of humoral agents on the myoelectrical activity of the terminal ileum

Neurally mediated propagating discrete clustered contractions superimposed on myogenic ripples in ex vivo segments of human ileum

Narrow muscle strips have been extensively used to study intestinal contractility. Larger specimens from laboratory animals have provided detailed understanding of mechanisms that underlie patterned intestinal motility. Despite progress in animal tissue, investigations of motor patterns in large, intact specimens of human gut ex vivo have been sparse. In this study, we tested whether neurally dependent motor patterns could be detected in isolated specimens of intact human ileum. Specimens (n = 14; 7-30 cm long) of terminal ileum were obtained with prior informed consent from patients undergoing colonic surgery for removal of carcinomas. Preparations were set up in an organ bath with an array of force transducers, a fiberoptic manometry catheter, and a video camera. Spontaneous and distension-evoked motor activity was recorded, and the effects of lidocaine, which inhibits neural activity, were studied. Myogenic contractions (ripples) occurred in all preparations (6.17 ± 0.36/min). They were of low amplitude and formed complex patterns by colliding and propagating in both directions along the specimen at anterograde velocities of 4.1 ± 0.3 mm/s and retrogradely at 4.9 ± 0.6 mm/s. In five specimens, larger amplitude clusters of contractions were seen (discrete clustered contractions), which propagated aborally at 1.05 ± 0.13 mm/s and orally at 1.07 ± 0.09 mm/s. These consisted of two to eight phasic contractions that aligned with ripples. These motor patterns were abolished by addition of lidocaine (0.3 mM). The ripples continued unchanged in the presence of this neural blocking agent. These results demonstrate that both myogenic and neurogenic motor patterns can be studied in isolated specimens of human small intestine.

Stimulated pressure response of the ileocolonic junctional zone and its use as a continence mechanism in a canine model

Mechanisms for maintaining passive continence in the efferent limb of urinary diversions include compression of tissue, peristalsis, equilibration of pressure and use of valves. Motor activity and pressure in the ileum, ileocecal valve (ICV) and the colon were evaluated in dogs. Spontaneous activity and pressure were compared with stimulated pressure response and activity. Stimulation was performed at the pelvic nerve and the small nerves in the mesenterium, as well as direct neurostimulation of the bowel. Resting pressure at the ICV was 12.7 +/- 0.4 cmH2O rising to 26.4 +/- 2.2 cmH2O during spontaneous depolarization. Stimulation of the pelvic nerve resulted in increased colonic motor activity with unchanged pressure. Electric stimulation of small mesenterical nerves to the ICV increased pressure in the ICV to 35.0 +/- 4.1 cmH2O, while direct myoelectric stimulation of the ICV zone increased the intraluminal pressure to 75.0 +/- 3.2 cmH2O. Termination of the electric stimulation was followed by a slow decrease of pressure to the resting level over a period of 30-45 s. Maintaining continence at the ICV with long-term constant or intermittent stimulation seems feasible.

Ileal pelvic reservoir: a correlation between motor patterns and clinical behaviour

An attempt has been made to correlate motility patterns of the pelvic ileal reservoir with patients' clinical experience. In order to evaluate the motility characteristics of the ileal reservoir, we have related its behaviour to the motility pattern observed in ileum proximal to an ileostomy. Seven patients with an ileostomy and 11 patients with a pelvic ileal reservoir have been investigated. The ileum and ileal reservoir were found to behave similarly during the fasting state and in response to distension and eating; however, a quantitative functional difference was discovered. Distension with 30 ml was enough to produce forceful contractions in the normal ileum, while a mean of 322 ml was necessary to initiate similar activity in the ileal reservoir. The ileal reservoir thus behaves as a capacitance organ with the ability to distend without contraction before a considerable volume has accumulated within it. When it does contract, it initiates a sensation of impending evacuation, but escape of ileal content is opposed by active contraction of the intact external anal sphincter.

Large bowel myoelectrical activity in man

The myoelectrical activity of human colon and rectum has been studied by three types of electrode in man--intraluminal (suction), serosal and cutaneous. The patterns obtained indicate a high degree of consistency between the methods and the value of surface electrodes is emphasized. Gradient along the large bowel of both frequency and percentage electrical activity have been observed and possible physiological roles are postulated for them. By correlating the features of regular electrical and corresponding regular motor waves an alteration in the myoelectrical pattern is observed in the region of the rectosigmoid junction.

Hormonal control of gastrointestinal motility

The motor responses of the gastrointestinal tract to a meal are tuned to provide the optimal conditions for digestion and absorption of food. Hormones released from the mucosa of the intestinal tract play an important role in regulating and integrating the various motor events which occur. Complex feedbacks, both nervous and humoral, control the release of intestinal hormones and also modify their actions. Preliminary studies suggest that abnormalities in the secretion or action of various gastrointestinal hormones may play an important role in the production of motor disorders of the gastrointestinal tract.

Electrical activity of gastrointestinal smooth muscle

Images

The electrical and motor actions of gastrointestinal hormones on the duodenum in man

The electrical and motor activity was recorded from the duodenum in 16 conscious human subjects in resting conditions. The main electrical wave form variously known as the pace-setter potential or slow wave was constantly present and periodically accompanied by a second electrical trace consisting of rapid bursts of fast waves or action potentials which were related to motor waves. Secretin and the synthetic analogue of gastrin, pentagastrin, were given in separate tests and their complementary actions on myoelectrical activity are reported. In general, secretin (in six subjects) depressed and pentagastrin (in eight subjects) enhanced motor activity and bursts of action potentials.