Relationship between in-vitro studies of gastrointestinal muscle and motility of the alimentary tract in vivo

Assessment of intestinal peristalsis in vitro

The protocol detailed in this unit is designed to assess intestinal peristaltic motility in the isolated small intestine in vitro and to measure the effects of drugs able to interfere with gut propulsive activity. The procedure is based on Trendelenburg's classic technique, described at the beginning of the 20th century in the isolated guinea pig ileum and, later on, extended to other intestinal preparations from the same animal and other animal species. This unit illustrates the basic procedures for setting up the intestinal preparation, recording peristalsis under near-physiologic conditions, and testing the pharmaco-toxicological effects of drugs and pollutants on the contractile behavior of the gut wall. The protocol allows evaluating the action of drugs affecting sensory and/or motor neurons of the enteric nervous system and how these neurons control the development of the motor program of the gut wall. This model can be exploited to investigate novel compounds undergoing preclinical development and both inhibitors and stimulants of gastrointestinal peristaltic activity, as well as environmental or alimentary pollutants, like xenobiotics and naturally-occurring toxins, endowed with noxious activity with regard to digestive functions.

The Effects of Various Peptides on Human Isolated Gut Muscle

The effects of eleven peptides of gastrointestinal origin have been studied on the contraction, relaxation and spontaneous activity of circular and longitudinal muscle strips from different regions of the human gastrointestinal tract. The effects varied with the peptides and sometimes with the region and muscle layer. There was either contraction, no effect, or relaxation and/or inhibition of an acetylcholine-induced contraction. Responses to some peptides are consistent with the possibility that they may contribute directly to the control of motility: galanin, neurotensin and substance P might be involved in contraction, and vasoactive intestinal peptide, peptide histidine isoleucine and peptide histidine methionine might be inhibitory transmitters.

Assessment of gastrointestinal motility using three different assays in vitro

The protocols detailed in this unit are designed to assess the motor activity of different gastric and intestinal muscle preparations in vitro and the effects of drugs that modulate gastrointestinal motility. The preparations described are characterized by different contractile behaviors, consisting of spontaneous (duodenum), neurogenic (ileum), and drug-stimulated (fundus, ileum) motility; these reproduce motility patterns occurring in the gut wall in vivo. These protocols document the variety of factors that can influence the responses of isolated tissues and describe how such tissues can be used for testing substances that affect gut movements. These preparations allow evaluation of direct interactions with the processes that control contractile machinery, as well as indirect effects resulting from the modification of neurotransmitter release from myenteric neurons. These models can be exploited to assay novel compounds undergoing preclinical development or to evaluate the functional toxicity exerted by environmental or alimentary pollutants, like xenobiotics and naturally occurring toxins, as well as the mechanisms underlying these effects.

Effect of transdermal application of nicotine on colonic transit in healthy nonsmoking volunteers

The radio-opaque marker technique (ROMT) is a safe and noninvasive method to determine total colonic (TCTT) and segmental colonic transit times (SCTT). Previous results have shown that smoking volunteers had significantly longer TCTT than nonsmokers, but the underlying mechanism was not clear. We investigated the effect of transdermal nicotine application in two different doses in a non-blind randomized experiment involving three distinct phases. In phase 1 baseline transit times were determined with an abdominal X-ray after a 6-day period of marker ingestion and again after the following bowel movement to study the influence of a bowel movement just before the X-ray. TCTT was nearly twice as high before than after defaecation (42.6 h vs. 25.1 h, P < 0.05). The main acceleration was found in the rectosigmoid (RS) (18.6 h vs 7.1 h, P < 0.05) with no significant changes in right (RC) and left colon (LC). In phase 2 and 3 nicotine was applied in two doses of 17.5 mg day-1 and 35 mg day-1 in random order. Both doses resulted in a significant decrease of TCTT compared to the predefaecation baseline (42.6 h vs 32.2 h/28.2 h, respectively, P < 0.05). Again the main effect was located in the RS (18.6 h vs 9.9 h/7.6 h, P < 0.05). Short-term application nicotine results in a decrease of TCTT which is due to an accelerated transit in the RS.

Neuropeptides in the internal anal sphincter in neurogenic faecal incontinence

The internal anal sphincter has both an intrinsic and extrinsic innervation which modulates its activity. While the nature of the extrinsic innervation has been well characterised, the same is not true of the intrinsic innervation. Although a variety of neurotransmitters have been identified in the human internal anal sphincter, their physiological role in health, and possible involvement in disease processes, have received little attention. Using immunohistochemistry we have studied the distribution and nerve fibre densities of a range of neuropeptides in the internal anal sphincter from 12 cancer patients (controls) and from 16 patients with neurogenic faecal incontinence. We have also studied the in vitro effect of vasoactive intestinal peptide, neuropeptide tyrosine, and galanin on isolated preparations of the internal anal sphincter from 11 cancer controls and 5 patients with neurogenic faecal incontinence. There was no difference in either the distribution or density of the neuropeptides between the 2 groups of patients, and there was no qualitative difference in the in vitro responses of the sphincter to the neuropeptides. These findings suggest that these neuropeptide components of the intrinsic innervation of the internal anal sphincter are unaffected in patients with neurogenic faecal incontinence.

The effects of cholecystokinin octapeptide on human isolated alimentary muscle

1. We studied cholecystokinin octapeptide (CCK-OP) for its motor effects and sites of action on human isolated muscle from stomach, small intestine and colon. 2. CCK-OP induced a concentration-dependent contraction of all the longitudinal muscles and of circular muscle from the stomach and large intestine. The peptide acted directly on these muscles at a site not involving muscarinic receptors. 3. CCK-OP relaxed the circular muscle of the small intestine and/or reduced the contractions to acetylcholine, by stimulating intramural postganglionic inhibitory neurones.

Proximal jejunal and distal ileal extrinsic innervation in the rabbit and dog

The varying patterns of motor behaviour of isolated and interposed jejunal and ileal segments in the rabbit and the dog previously reported (Jenkins and Macleod, 1970) were examined by selective denervation techniques. One hundred and twenty-three paired experiments were conducted on rabbits and 55 similar experiments were performed on dogs.

Length-matched paired segments of proximal jejunum and distal ileum were isolated and filled with saline at a constant rate. Segmental resistance to filling was regarded as an index of tone. The influence of vagotomy and of sympathectomy on the tone of the segments was studied in segments supplied by one or by two vessels.

Vagotomy caused a decrease in tone in the proximal jejunal segments, while sympathectomy had little effect. In segments of distal ileum sympathectomy resulted in segments behaving in a similar fashion, while vagotomy had an unpredictable effect on tone.

The results suggest a uniform distribution of the vagus to the whole length of the small bowel in the rabit and the dog, serving to maintain the tone of the bowel. It is deduced that sympathetic supply to the proximal jejunum isabsent in these animkals and is distributed to the distal ileum only in an irregular fashion.

The relevance of these observations to the clinical use of interposed small-bowel segments is considered.

Effect of prostaglandins E1 and E2 on intestinal motility in the guinea-pig and rat

1. Prostaglandins E(1) and E(2) affected intestinal activity both in vitro and in vivo.2. Serosal application of prostaglandin to guinea-pig isolated ileum stimulated the longitudinal muscle but reduced peristaltic contractions of the circular muscle and the propulsion of fluid through the gut. Intraluminal application had little effect.3. Injection of prostaglandin into the bloodstream of anaesthetized rats stimulated the longitudinal muscle of the ileum and increased the intraluminal pressure. A similar response sometimes occurred in the guinea-pig, but in general the effect was variable.4. Release of prostaglandin in the gut wall, but probably not into the blood or into the lumen of the gut, may play a part in controlling intestinal motility.