Origin and control of gastrointestinal motility

Importance of the enteric nervous system in the control of the migrating motility complex

The migrating motility complex (MMC), a cyclical phenomenon, represents rudimentary motility pattern in the gastrointestinal tract. The MMC is observed mostly in the stomach and gut of man and numerous animal species. It contains three or four phases, while its phase III is the most characteristic. The mechanisms controlling the pattern are unclear in part, although the neural control of the MMC seems crucial. The main goal of this article was to discuss the importance of intrinsic innervation of the gastrointestinal tract in MMC initiation, migration, and cessation to emphasize that various MMC-controlling mechanisms act through the enteric nervous system. Two main neural regions, central and peripheral, are able to initiate the MMC. However, central regulation of the MMC may require cooperation with the enteric nervous system. When central mechanisms are not active, the MMC can be initiated peripherally in any region of the small bowel. The enteric nervous system affects the MMC in response to the luminal stimuli which can contribute to the initiation and cessation of the cycle, and it may evoke irregular phasic contractions within the pattern. The hormonal regulators released from the endocrine cells may exert a modulatory effect upon the MMC mostly through the enteric nervous system. Their central action could also be considered. It can be concluded that the enteric nervous system is involved in the great majority of the MMC-controlling mechanisms.

Comparison of antispasmodic effect of hydroalcoholic extract of Dracocephalum kotschyi Boiss. in rat uterus and ileum

Dracocephalum kotschyi Boiss. is a traditional medicine with antispasmodic activities. The objective of this research was to study antispasmodic activities of hydroalcoholic extract of D. kotschyi on rat isolated uterus contractions for comparison with isolated ileum. Hydroalcoholic extract was obtained from aerial part of D. kotschyi using percolation method. A portion of rat ileum or uterus was suspended in Tyrode's solution at 37°C and gassed with O₂. Effect of D. kotschyi extract was assessed on ileum or uterus contractions induced by KCl (80 mM), acetylcholine (ACh, 500 nM), electrical field stimulation (EFS) or oxytocin (0.0005 IU/mL). The extract of D. kotschyi concentration-dependently inhibited ileum responses to KCl (IC₅₀ = 65 ± 18 μg/mL), ACh (IC₅₀ = 102 ± 18 μg/mL) and EFS (IC₅₀ = 117 ± 29 μg/mL). The extract of D. kotschyi also concentration-dependently inhibited uterus responses to KCl (IC₅₀ = 453 ± 64μg/mL), ACh (IC₅₀ = 58 ± 9 μg/mL), EFS (IC₅₀ = 22 ± 3 μg/mL) as well as oxytocin (IC₅₀ = 70 ± 11 μg/mL). From this experiment it was concluded that D. kotschyi extract possesses antispasmodic activities on both smooth muscle of ileum and uterus. In comparison, the extract was more effective inhibitor of ACh and EFS responses in rat uterus than on the ileum. On the other hand, the extract was a more potent inhibitor of KCl response on rat ileum. However, the extract was found to be a potent inhibitor of oxytocin-induced contraction of rat uterus. These results indicate that D. kotschyi extract may contain components that might be useful lead compounds for prevention of uterus spasm.

Nissen fundoplication improves gastric myoelectrical activity characteristics and symptoms in gastroesophageal reflux patients: evaluation in transcutaneous electrogastrography

BACKGROUND

Gastric myoelectrical activity disorders play an essential role in the pathophysiology of gastroesophageal reflux disease (GERD), although little is known about gastric motility following surgical treatment of the disease. The aim of present study was to analyze the impact of Nissen fundoplication on both gastric myoelectrical activity, measured using the transcutaneous electrogastrography technique (EGG), and change in digestive symptoms.

METHODS

In 43 patients with GERD, EGG was recorded before and after the Nissen procedure and compared with the EGG obtained in eight healthy volunteers. Symptoms of epigastric pain, belching, regurgitation, heartburn, postprandial abdominal distension, and early satiety were recorded. At a three-week and a one-year postoperative follow-up, these tests were repeated.

RESULTS

In fasted patients before the operation, the slow-wave frequency distribution (normogastria, 53.7%; bradygastria, 44.2%; dysrhythmia, 47.1%) was significantly different compared with that of controls (89.2%, 7.0%, and 10.4%, respectively). No major changes in slow-wave frequency distribution were observed after a meal in examined patients, besides a significant rise in tachygastria (12.4%). Three weeks following the Nissen fundoplication, the fasting slow-wave frequency distribution did not change significantly compared with the preoperative period, being 58.1% for normogastria, 43.2% for bradygastria, and 12.0% for tachygastria. The abnormal distribution of slow waves (bradygastria + tachygastria) was not significantly affected by Nissen fundoplication, being 47.1% before and 44.9% after the operation, respectively. At the same time and still one year after operation there was a significant improvement in all clinical symptoms measured.

CONCLUSION

EGG showed that Nissen fundoplication influenced and might improve the slow-wave generation in gastric pacemaker. Dyspeptic symptoms were also improved up to one year postoperatively.

Opioid-induced bowel dysfunction: pathophysiology and potential new therapies

Opioid treatment for postoperative or chronic pain is frequently associated with adverse effects, the most common being dose-limiting and debilitating bowel dysfunction. Postoperative ileus, although attributable to surgical procedures, is often exacerbated by opioid use during and following surgery. Postoperative ileus is marked by increased inhibitory neural input, heightened inflammatory responses, decreased propulsive movements and increased fluid absorption in the gastrointestinal tract. The use of opioids for chronic pain is characterised by a constellation of symptoms including hard dry stools, straining, incomplete evacuation, bloating, abdominal distension and increased gastroesophageal reflux. The current management of opioid-induced bowel dysfunction among patients receiving opioid analgesics consists primarily of nonspecific ameliorative measures. Intensive investigations into the mode of action of opioids have characterised three opioid receptor classes -mu, delta and kappa- that mediate the myriad of peripheral and central actions of opioids. Activation of mu-opioid receptors in the gastrointestinal tract is responsible for inhibition of gut motility, whereas receptors in the central nervous system mediate the analgesic actions of opioids. Blocking peripheral opioid receptors in the gut is therefore a logical therapeutic target for managing opioid-induced bowel dysfunction. Available opioid antagonists such as naloxone are of limited use because they are readily absorbed, cross the blood-brain barrier, and act at central opioid receptors to reverse analgesia and elicit opioid withdrawal. Methylnaltrexone and alvimopan are recently developed opioid antagonists with activity that is restricted to peripheral receptors. Both have recently shown the ability to reverse opioid-induced bowel dysfunction without reversing analgesia or precipitating central nervous system withdrawal signs in non-surgical patients receiving opioids for chronic pain. In addition, recent clinical studies with alvimopan suggest that it may normalise bowel function without blocking opioid analgesia in abdominal laparotomy patients with opioid-related postoperative ileus.

Effect of the acupoints ST-36 (Zusanli) and SP-6 (Sanyinjiao) on intestinal myoelectric activity of Wistar rats

Despite its ancient use as a therapeutic tool to treat several ailments, acupuncture still faces the challenge of scrutiny by Western science both in terms of its efficacy and in terms of the characterization of its effects and mechanisms of actions underlying these effects. We investigated under well-controlled and carefully characterized conditions the influence of electrical stimulation of acupuncture points ST-36 (Zusanli) and SP-6 (Sanyinjiao) on the myoelectric activity of the small intestine of 38 adult male Wistar rats. Electrical recordings obtained by means of four electrodes chronically implanted in the small intestine were used to assess the effects of acupuncture (electroacupuncture stimulation set at 2 Hz, intermittent stimulation, 1 V, for 30 min). Immobilization of the animals was associated with a consistent decrease (-8 +/- 7%) in the myoelectric activity of the small intestine as measured by means of the root mean square. Conversely, acupuncture was able to significantly increase (overshoot) this activity compared to baseline (+44 +/- 7%). In contrast, immobilized animals subjected to sham acupuncture had only modest (nonsignificant) increases in myoelectric activity (+9 +/- 6%). Using carefully controlled conditions we confirmed previous noncontrolled studies on the ability of acupuncture to alter intestinal motility. The characterization of the topographic and temporal profiles of the effects observed here represents a basis for future dissection of the physiological and pharmacological systems underlying these effects.

Effect of surgical alteration of the rat gastrointestinal tract on the growth and development of Hymenolepis diminuta

Eight groups of rats were used to study the involvement of the enteric (ENS) and central (CNS) nervous systems in the development of Hymenolepis diminuta using surgical intestinal transection, or CNS denervation, or both procedures. The transection procedure was used to isolate the ENS of the small intestine from either orad and/or caudal portions of the alimentary system, while the CNS denervation was used to eliminate direct visceral efferent inputs from the CNS. Nine days after the surgical procedures, all rats were infected with 35 cysticercoids of H. diminuta. On 20 days postinfection, the infection intensity, tapeworm dry weight, tapeworm morphology, intestine length, and intestinal wet weight were recorded. Only the combination of the duodenal and ileal transections with a CNS denervation reduced infection intensity and prevented the increased intestinal length normally observed in infected rats. In contrast, none of the various intestinal transection procedures alone or CNS denervation alone had any effect on the survival, ability to produce oncospheres or morphology of the tapeworms. In conclusion, tapeworm survival is decreased when both CNS and ENS inputs into the small intestine are altered or absent.

Mechanism of carbon monoxide-induced relaxation in the guinea pig ileal smooth muscle

The mechanism of carbon monoxide (CO)-induced relaxation were investigated in the guinea-pig ileum. CO (10%) inhibited the 40 mM KCl-induced contraction. This effect was antagonized by ODQ (1 microM), a soluble guanylate cyclase inhibitor. In contrast, CO did not inhibit the 40 mM KCl-induced increase in cytosolic Ca2+ level ([Ca2+]i). Cumulative addition of KCl induced a graded increase in both [Ca2+]i and muscle tension. In the presence of CO, the increase in muscle tension was attenuated whereas the increase in [Ca2+]i was only slightly decreased. Thus, the [Ca2+]i-tension relationship constructed by cumulative addition of KCl shifted downwards in the presence of CO. Using the patch clamp, CO was found to have little effect on the peak Ba currents (I(Ba)) when voltage was stepped from -60 mV to 0 mV. From these results, we conclude that CO inhibits contraction of guinea-pig ileum mainly by the decrease in the sensitivity of contractile elements to Ca2+ via a cyclic GMP-dependent pathway but not by the inhibition of L-type Ca2+ channel.

ATP and nitric oxide: inhibitory NANC neurotransmitters in the longitudinal muscle-myenteric plexus preparation of the rat ileum

1. The nature of neurotransmitter(s) involved in non-adrenergic non-cholinergic (NANC) relaxations induced by electrical stimulation (10 s trains, 1-8 Hz) was investigated in the precontracted longitudinal muscle-myenteric plexus preparation of the rat ileum. 2. Electrical stimulation of the tissue induced complex responses, consisting of a primary contraction, a primary relaxation, an off-relaxation and a rebound contraction, which were all tetrodotoxin(TTX)-sensitive. 3. Vasoactive intestinal polypeptide (VIP) and carbon monoxide (CO) did not induce relaxations. alpha-Chymotrypsin did not reduce the relaxations induced by electrical stimulation, while zinc protoporphyrin IX had non-specific effects. 4. Nitric oxide (NO) induced concentration-dependent relaxations. NG-nitro-L-arginine methylester (L-NAME) abolished the primary contractions and off-relaxations, while it partially reduced the primary relaxations. 5. ATP induced relaxations and ATP-desensitization of the tissues partially reduced the primary relaxations. Suramin and reactive blue 2 did not consistently influence the primary relaxations. 6. The ATP-induced relaxations were not influenced by L-NAME or TTX. The inhibitory effect of ATP-desensitization and L-NAME did not summate. 7. The cyclic AMP content of the tissue did not increase upon electrical stimulation or after addition of NO or ATP. The cyclic GMP content of the tissue increased upon electrical stimulation and addition of NO, but not after addition of ATP. 8. It is concluded that the relaxation induced by electrical stimulation consists of two types of responses. The off-relaxation is completely nitrergic, while the primary relaxation is mediated by NO, ATP and an as yet unknown transmitter which is not VIP or CO.

Review article: the use of botulinum toxin in the alimentary tract

New and future indications for the treatment of disorders of the alimentary tract using local injections of botulinum toxin are reviewed. Clinical experience shows that overactive smooth muscle sphincters may be weakened to treat disorders such as achalasia or chronic anal fissure. By contrast, injections placed into the sphincter of Oddi have proven less effective for postcholecystectomy pain syndrome. Experimental evidence suggests that food intake may be reduced by weakening the distal stomach with botulinum toxin. This approach may possibly lead to the treatment of obesity. There are some new possible indications for the use of botulinum toxin on the alimentary tract, and infantile hypertrophic pyloric stenosis seems to be the most promising new development.