Multiple-balloon kymographic recording of the comparative action of demerol, morphine and placebos on the motility of the upper small intestine in man

Exercise and gastrointestinal function and disease: an evidence-based review of risks and benefits

BACKGROUND & AIMS

Exercise is beneficial to health because it reduces the risk of cardiovascular and endocrine diseases, improves bone and muscle conditioning, and lessens anxiety and depression. However, the impact of exercise on the gastrointestinal system has been conflicting. This systematic literature review evaluates the effect of the different modes and intensity levels of exercise on gastrointestinal function and disease using an evidence-based approach. Although more applicable to trained athletes and individuals who are highly active and, as such, at risk to experience the side-effects of exercise, an effort was made to state the level or degree of exercise or the lack of such evidence.

RESULTS

Light and moderate exercise is well tolerated and can benefit patients with inflammatory bowel disease and liver disease. Physical activity can also improve gastric emptying and lower the relative risk of colon cancer in most populations. Severe, exhaustive exercise, however, inhibits gastric emptying, interferes with gastrointestinal absorption, and causes many gastrointestinal symptoms, most notably gastrointestinal bleeding.

CONCLUSIONS

This knowledge will enable physicians to prescribe physical exercise in health and disease and to better manage patients with exercise-related gastrointestinal disorders. Our understanding of exercise and its gastrointestinal manifestations as well as risks and benefits warrants further investigation.

Is the gut an athletic organ? Digestion, absorption and exercise

Digestion is a process which takes place in resting conditions. Exercise is characterised by a shift in blood flow away from the gastrointestinal (GI) tract towards the active muscle and the lungs. Changes in nervous activity, in circulating hormones, peptides and metabolic end products lead to changes in GI motility, blood flow, absorption and secretion. In exhausting endurance events, 30 to 50% of participants may suffer from 1 or more GI symptoms, which have often been interpreted as being a result of maldigestion, malabsorption, changes in small intestinal transit, and improper food and fluid intake. Results of field and laboratory studies show that pre-exercise ingestion of foods rich in dietary fibre, fat and protein, as well as strongly hypertonic drinks, may cause upper GI symptoms such as stomach ache, vomiting and reflux or heartburn. There is no evidence that the ingestion of nonhypertonic drinks during exercise induces GI distress and diarrhoea. In contrast, dehydration because of insufficient fluid replacement has been shown to increase the frequency of GI symptoms. Lower GI symptoms, such as intestinal cramps, diarrhoea--sometimes bloody--and urge to defecate seem to be more related to changes in gut motility and tone, as well as a secretion. These symptoms are to a large extent induced by the degree of decrease in GI blood flow and the secretion of secretory substances such as vasoactive intestinal peptide, secretin and peptide-histidine-methionine. Intensive exercise causes considerable reflux, delays small intestinal transit, reduces absorption and tends to increase colonic transit. The latter may reduce whole gut transit time. The gut is not an athletic organ in the sense that it adapts to increased exercise-induced physiological stress. However, adequate training leads to a less dramatic decrease of GI blood flow at submaximal exercise intensities and is important in the prevention of GI symptoms.

Changes in opioid receptor selectivity following processing of peptide E: effect on gut motility

Peptide E is a mu-selective opioid peptide derived from proenkephalin A which contains [Met5]-enkephalin at the amino end and [Leu5]-enkephalin at the carboxyl end. Peptide E is further processed both centrally and peripherally to a [Leu5]-enkephalin-containing fragment which was investigated to determine if processing leads to alterations in receptor selectivity. Peptide E-(15-25) inhibited electrically stimulated contractions in both the mouse vas deferens, longitudinal muscle, myenteric (IC50 = 459 nmol/L), and guinea pig ileum (IC50 = 2630 nmol/L), indicating a sixfold delta-receptor selectivity. When administered intracerebroventricularly to mice, peptide E-(15-25) also produced potent analgesia which was completely antagonized by naloxone pretreatment, but the peptide had no effect on intestinal transit as measured by the radiochromium geometric center method. This is consistent with earlier findings that intracerebroventricular delta-opioid-selective agents are analgesic but do not inhibit intestinal transit. In vitro radioligand binding assays were performed using male Sprague-Dawley rat whole brain homogenates. The IC50 for peptide E against [3H]naloxone was 1.8 nmol/L compared with the delta-opioid ligand, [3H] [D-Pen2, D-Pen5]-enkephalin of 38.8 nmol/L. The IC50 for peptide E-(15-25) against [3H]naloxone was 497 nmol/L, but for [3H] [D-Pen2, D-Pen5]-enkephalin it was 50.6 nmol/L. Therefore, peptide E loses mu-opioid receptor affinity (1.8-497 nmol/L) after proteolytic processing and the loss of the amino terminal tyrosine but maintains a high delta-opioid affinity (38.8-50.6 nmol/L). These studies demonstrate that enzymatic peptide processing of peptide E to peptide E-(15-25) leads to a shift from mu- to delta-receptor selectivity and a different spectrum of biological effects on gut motility.

Effect of analgesic drugs on the electromyographic activity of the gastrointestinal tract and sphincter of Oddi and on biliary pressure

Continuous biliary pressure and electromyographic activity of the sphincter of Oddi and gastrointestinal tract were recorded in conscious opossums following administration of analgesic drugs. Morphine, meperidine, and pentazocin increased significantly the duration of the migrating motor complex (MMC) cycle. Periods of 1-2 minutes of intense burst of spike potentials were seen in the sphincter of Oddi and duodenum following administration of morphine (8 experiments), meperidine (6 experiments), and pentazocin (3 experiments). The biliary pressure in the control studies was similar to that following administration of all analgesics in the animals with gallbladder and following instillation of tramadol, metamizol, and acetylsalicylic acid in animals with no gallbladder. However, the biliary pressure was significantly higher following administration of morphine, meperidine, and pentazocin in the animals with no gallbladder. It is concluded from this study that morphine, meperidine, and pentazocin may cause important disturbances in the motility of the sphincter of Oddi and gastrointestinal tract. These myoelectric disturbances may cause an increase in the biliary pressure in animals that have been subjected to cholecystectomy, but not in animals with intact gallbladder. The gallbladder may accommodate the bile produced by the liver during periods of sphincter of Oddi dysfunction and thus impede an increase in the biliary pressure.

Opioid activities of human beta-casomorphins

Opioid activities of human beta-casomorphin-4, -5, -7 and -8 and, for comparison, of the corresponding bovine beta-casomorphins were studied in the guinea-pig ileum preparation. Binding parameters, i.e. KD-values and binding site concentrations, for the interaction of human and bovine beta-casomorphins with opioid receptors in rat brain homogenates were determined in inhibition experiments, using [3H]-(D-Ala2, MePhe4, Gly-ol5)enkephalin, [3H]-(D-Ala2, D-Leu5)enkephalin and [3H]ethylketazocin as mu-, delta- and kappa-opioid receptor ligands. Analysis of binding data was performed using a non-linear curve fitting program. All beta-casomorphins examined displayed opioid activity. The affinity was highest for mu-receptors, less so for delta-receptors and lowest for kappa-receptors. It is suggested that human beta-casomorphins might play a role as "food hormones".

Effects of morphine and atropine on motility and transit in the human ileum

We examined motility of the ileocecal region, pressures at the ileocecal sphincter, and ileal flow after therapeutic doses of morphine and atropine. Using a factorial design in two cells of 8 (2(3] subjects, drugs were given during fasting and postcibally. Morphine (100 micrograms/kg body wt as a bolus intravenously) and atropine (7 micrograms/kg body wt as a bolus) stimulated migrating bursts of phasic activity (similar to phase III of the migrating motor complex). Morphine initially stimulated ileal flow, but atropine could not be shown to have this effect. Atropine reduced markedly the occurrence of sporadic pressure waves in the ileum, but morphine did not. Whereas atropine delayed mouth-to-ileum transit of polyethylene glycol, given in a mixed meal, morphine did not. Naloxone, in the dosage used (40 micrograms/kg body wt as a bolus, followed by 10 micrograms/kg body wt X h) had no independent effects on motility or flow, but did blunt the stimulatory effects of morphine and atropine on migrating motor complexes. We could not demonstrate an effect of any drug on the transit of lactulose from terminal ileum to cecum. Neither morphine nor atropine had impressive effects on tone at the ileocecal sphincter. These observations, while not specifying the mechanisms for constipation after opiates or anticholinergics, highlight the complexities of small bowel transit in humans and point out that the antidiarrheal effects of drugs are probably multifactorial.

Use of gut cyclic motor activity to evaluate a stimulant (narcotic) and inhibitor (anticholinergic) of gastrointestinal-tract activity in the unanesthetized dog

The use of gut cyclic motor activity to evaluate both a stimulant and inhibitor of gastrointestinal contractile activity in the unanesthetized dog is described. In the interdigestive (fasted) state, there is a cyclic alternation of intense periods of contractions (burst) with quiescent periods (basal). Codeine phosphate, a narcotic agent, caused a dose-dependent increase in the number and duration of circular muscle contractions when administered in the basal phase. Hyoscine N-butyl-bromide, an anticholinergic drug, caused a dose-dependent reduction in both amplitude and frequency of burst-phase contractions. When a combination of codeine phosphate and hyoscine N-butylbromide was administered simultaneously in the basal or burst phase, the hyoscine N-butylbromide prevailed and had the dominant effect. This is a useful in vivo model to evaluate the effects of drugs on the gastrointestinal tract.

Effect of prolonged exercise on the passage of a solid meal through the stomach and small intestine

The effect of intermittent moderate exercise on the passage of a solid meal, labelled with radioactive Technetium sulphur colloid, through the stomach and small intestine was investigated by paired studies on seven healthy volunteers. Measurements of gastric radioactivity and breath hydrogen exertion were recorded every 10 minutes while subjects exercised in a controlled manner while seated on a bicycle ergometer. These were compared with values obtained during a separate experiment while the same subjects sat upright in a chair. Exercise significantly accelerated gastric emptying (control t 1/2 = 1.5 +/- 0.1 h; exercise t 1/2 = 1.2 +/- 0.1 h; p less than 0.02) but had no significant effect on small bowel transit time.