Is the action of cisapride on the guinea-pig ileum mediated via 5-HT4 receptors?

Pharmacological basis for the medicinal use of psyllium husk (Ispaghula) in constipation and diarrhea

BACKGROUND

The objective of this study was to determine the pharmacological basis of the medicinal use of psyllium husk (Ispaghula) in gastrointestinal motility disorders.

METHODS

In-vivo studies were conducted on mice, and isolated rabbit jejunum and guinea-pig ileum were used in in-vitro experiments.

RESULTS

The crude extract of Ispaghula (Po.Cr) had a laxative effect in mice at 100 and 300 mg/kg, which was partially sensitive to atropine or SB203186 (5-HT(4) antagonist). At higher doses (500 and 1,000 mg/kg), Po.Cr had antisecretory and antidiarrheal activity. In guinea-pig ileum, Po.Cr (1-10 mg/ml) had a stimulatory effect, which was partially sensitive to atropine or SB203186. In rabbit jejunum, Po.Cr had a partially atropine-sensitive stimulatory effect followed by relaxation at 10 mg/ml. The relaxation was inhibited by the presence of L-NAME, a nitric oxide (NO) synthase inhibitor, or methylene blue, a guanylyl cyclase inhibitor. Similarly, the relaxant effect of Po.Cr on K(+) (80 mM)-induced contractions, was attenuated in the presence of L-NAME or methylene blue. Activity-directed fractionation of Po.Cr revealed that the gut stimulatory and inhibitory constituents were widely distributed in the aqueous and organic fractions.

CONCLUSION

This study demonstrates that Ispaghula has a gut-stimulatory effect, mediated partially by muscarinic and 5-HT(4) receptor activation, which may complement the laxative effect of its fiber content, and a gut-inhibitory activity possibly mediated by blockade of Ca(2+) channels and activation of NO-cyclic guanosine monophosphate pathways. This may explain its medicinal use in diarrhea. It is, perhaps, also intended by nature to offset an excessive stimulant effect.

Role of serotonin in the pathophysiology of the irritable bowel syndrome

The irritable bowel syndrome (IBS) is a complex disorder that is associated with altered gastrointestinal motility, secretion, and sensation. Serotonin (5-HT) is an important neurotransmitter and paracrine signalling molecule in the gastrointestinal tract. 5-HT release from enterochromaffin (EC) cells initiates peristaltic, secretory, vasodilatory, vagal and nociceptive reflexes. The enteric nervous system (ENS) comprises a semiautonomous effector system that is connected to the central autonomic network. Parasympathetic and sympathetic nerves modulate the ENS via afferent and efferent communications. Ongoing, bidirectional brain-gut interactions involving 5-HT pathways occur that significantly influence the effector systems. Altered 5-HT signalling may lead to both intestinal and extraintestinal symptoms in IBS. 5-HT directly and indirectly affects intestinal motor and secretory function and abnormalities may lead to either constipation or diarrhea. 5-HT modulates sensation and perception of visceral stimulation at peripheral and central sites. Therapeutic agents targeting altered 5-HT signalling may provide new, effective treatments for patients with IBS.

ERG K+ channels modulate the electrical and contractile activities of gallbladder smooth muscle

The current study was undertaken to test the existence and possible role of ether-a-go-go-related gene 1 (ERG1) protein K(+) channels in gallbladder smooth muscle (GBSM). Transcripts encoding ERG1 were detected in human, mouse, and guinea pig GBSM, and ERG1 immunoreactivity was observed in GBSM cells. In intracellular voltage recordings, addition of E-4031 (100 nM-1 microM) or cisapride (100 nM-2 microM) caused concentration-dependent excitation of guinea pig GBSM that was not affected by 500 nM TTX + 5 microM atropine, and E-4031 also depolarized the resting membrane potential. In muscle strip studies, E-4031 either induced phasic contractions or significantly increased the amplitude of phasic contractions in spontaneously active tissues (P = 0.001). E-4031 also potentiated bethanechol-induced contractions. In conclusion, ERG1 channels are expressed in the GBSM, where they play a role in excitation-contraction coupling probably by contributing to repolarization of the plateau phase of the action potential and to the resting membrane potential.

5-HT(4) receptors mediating enhancement of contractility in canine stomach; an in vitro and in vivo study

We aimed to study 5-HT(4) receptors in canine stomach contractility both in vivo and in vitro. In anaesthetized Beagle dogs, the selective 5-HT(4) receptor agonist prucalopride (i.v.) induced dose-dependent tonic stomach contractions under isobaric conditions, an effect that was antagonized by the selective 5-HT(4) receptor antagonist GR 125487 (10 microg kg(-1), i.v.). Electrical field stimulation (EFS) of corpus longitudinal muscle strips resulted in atropine- and tetrodotoxin-sensitive contractions (L-NOARG (0.1 mM) present in all organ bath solutions). Prucalopride increased these contractions (maximal response after single-dose addition (0.3 microM): 165% of initial value, or after cumulative addition: 188%). In the presence of methysergide (3 microM), 5-HT also increased EFS-contractions (after single-dose addition (0.3 microM): increase to 192%, after cumulative addition: 148%). The selective 5-HT(4) receptor antagonists GR 113808 (0.1 microM) or GR 125487 (10 nM) antagonized the prucalopride (0.3 microM)-induced contraction increments. When EFS-induced contractions were blocked by atropine or tetrodotoxin, prucalopride was ineffective. In the presence of methysergide (3 microM), the contraction increases to 5-HT (0.3 microM) were prevented by GR 113808 (0.1 microM). The prucalopride curve (pEC(50) 7.9) was shifted in parallel to the right by GR 113808 3 nM (pA(2) 9.4). In the presence of methysergide (3 microM), the curve to 5-HT (pEC(50) 8.1) was competitively antagonized by GR 113808, yielding a Schild slope of 0.8+/-0.2 (pK(B) of 9.1 with unit Schild slope). In corpus circular muscle strips, the prucalopride (0.3 microM)-induced augmentation of EFS-contractions (258%) was also prevented by GR 113808 (0.1 microM) (124%). In conclusion, the effects of 5-HT(4) receptor agonists on proximal stomach motor activity in vivo can be explained by an effect on 5-HT(4) receptors on cholinergic nerves within the gastric muscle wall.

Mechanisms for contractile effect of Dai-kenchu-to in isolated guinea pig ileum

The mechanisms by which Dai-kenchu-to (TJ-100), a kampo medicine, enhances gastrointestinal motility was investigated using isolated guinea pig ileum. TJ-100 induced contractions accompanied by autonomous contraction at a concentration of more than 3 x 10(-4) g/ml in a dose-related manner. The TJ-100-induced ileal contraction was suppressed by atropine and tetrodotoxin, but not by hexamethonium. This effect was partially suppressed in the presence of high concentrations of ICS 205-930, a serotonin 4 (5-HT4) receptor antagonist. In addition, TJ-100 showed an acetylcholine (ACh)-releasing action in the smooth muscle tissues of ileum. These results suggest that contractile response induced by TJ-100 is partially mediated by ACh released from the cholinergic nerve endings and that 5-HT4 receptors would be involved in the effect of TJ-100.

Structure of the human serotonin 5-HT4 receptor gene and cloning of a novel 5-HT4 splice variant

Several variants of the serotonin 5-HT4 receptor are known to be produced by alternative splicing. To survey the existence and usage of exons in humans, we cloned the human 5-HT4 gene. Based on sequence analysis seven C-terminal variants (a-g) and one internal splice variant (h) were found. We concentrated in this study on the functional characterization of the novel splice variant h, which leads to the insertion of 14 amino acids into the second extracellular loop of the receptor. The h variant was cloned as a splice combination with the C-terminal b variant; therefore, we call this receptor 5-HT4(hb). This novel receptor variant was expressed transiently in COS-7 cells, and its pharmacological profile was compared with those of the previously cloned 5-HT4(a) and 5-HT4(b) isoforms, with the latter being the primary reference for the h variant. In competition binding experiments using reference 5-HT4 ligands, no significant differences were detected. However, the broadly used 5-HT4 antagonist GR113808 discriminated functionally among the receptor variants investigated. As expected, it was an antagonist on the 5-HT4(a) and 5-HT4(b) variant but showed partial agonistic activity on the 5-HT4(hb) variant. These data emphasize the importance of variations introduced by splicing for receptor pharmacology and may help in the understanding of conflicting results seen with 5-HT4 ligands in different model systems.

Cisapride stimulates contraction of idiopathic megacolonic smooth muscle in cats

We have previously shown that cisapride, a substituted piperidinyl benzamide, stimulates contraction of healthy feline colonic smooth muscle. The purpose of the present investigation was to determine the effect of cisapride on feline idiopathic megacolonic smooth muscle function. Longitudinal smooth muscle strips from ascending and descending colon were obtained from cats with idiopathic megacolon, suspended in a 1.5 mM Ca(2+)-HEPES buffer solution (37 degrees C, 100% O2, pH 7.4), attached to isometric force transducers, and stretched to optimal muscle length (Lo). Control responses were obtained at each muscle site with acetylcholine (10(-8) to 10(-4) M), substance P (10(-11) to 10(-7) M), or potassium chloride (10 to 80 mM). Muscles were then stimulated with cumulative (10(-9) to 10(-6) M) doses of cisapride in the absence or presence of tetrodotoxin (10(-6) M) and atropine (10(-6) M), or in a 0 calcium HEPES buffer solution. In cats with idiopathic megacolon, cisapride stimulated contractions of longitudinal smooth muscle from both the ascending and the descending colon. Cisapride-induced contractions were similar in magnitude to those induced by substance P and acetylcholine in the ascending colon, but were less than those observed in the descending colon. Cisapride-induced contractions in megacolonic smooth muscle were only partially inhibited by tetrodotoxin and atropine, but were virtually abolished by removal of extracellular calcium. We concluded that cisapride-induced contractions of feline megacolonic smooth muscle are largely smooth muscle mediated and dependent on influx of extracellular calcium. Cisapride-induced contractions in megacolonic smooth muscle are only partially dependent on enteric cholinergic nerves. Thus, cisapride may be useful in the treatment of cats with idiopathic megacolon.

Effect of cisapride on the isolated guinea pig gall bladder and common bile duct

1. In this study, the effect of cisapride on the isolated guinea pig gall bladder (GB) and common bile duct (CBD) motility was investigated. 2. Cisapride, up to a certain concentration, produced an increase in tone of the GB (EC50 1.35 x 10(-8) M) and the CBD (EC50 2.75 x 10(-9) M), whereas, at concentrations higher than 3 x 10(-5) M for the GB and 5 x 10(-6) M for the CBD, it produced a transient increase in tone followed by a sustained decrease in tone or in the contraction amplitude or in both. 3. The cisapride-induced increase in tone was antagonized by atropine on both the GB and the CBD. 4. Cisapride up to 2 x 10(-5) M for the GB and 3 x 10(-6) M for the CBD did not modify, whereas, at concentrations higher than 2.8 x 10(-5) M for the GB and 4 x 10(-6) M for the CBD, it antagonized, noncompetitively, the concentration-response curve to exogenously applied acetylcholine. The IC50 values for cisapride on the EC50 of acetylcholine on the GB and the CBD were 9.4 x 10(-5) M and 8.2 x 10(-6) M, respectively. 5. In conclusion, on the guinea pig GB and CBD, low concentrations of cisapride produce a stimulating effect, probably of cholinergic origin, whereas higher concentrations produce a transient stimulating effect, probably of cholinergic origin, followed by a sustained relaxing effect, which may involve both cholinergic and noncholinergic pathways.

The effects of cisapride on elemental content in neonatal mouse small intestine in vivo

The effects of cisapride on elemental content of enterocytes, smooth muscle cells and lamina propria in neonatal mouse jejunum were studied using electron probe X-ray microanalysis. One hour after injection with cisapride (1.7 or 0.017 mg/kg body weight i.p.), Cl content was significantly reduced in villus base, crypt and smooth muscle cells and Na content decreased in muscle cells. No changes were observed in Na or Cl within villus tip cells. Total Ca content did not change significantly in any cell type following treatment with cisapride. These results confirm that cisapride induces net Cl- secretion in neonatal mouse jejunum.

Regulation of 60-kDa heat shock protein expression by systemic stress and 5-hydroxytryptamine in rat colonic mucosa

Bowel dysfunction such as irritable bowel syndrome caused by stress is well described. Previous reports suggest that 5-hydroxytryptamine (5-HT) mediates alteration of bowel motility. In this study, the effects of water-immersion stress and the administration of 5-HT on the expression of a 60-kDa heat shock protein (HSP60) in rat colonic mucosa were investigated. The effect of YM-060, a 5-hydroxytryptamine 3 (5-HT3) receptor antagonist, on the expression of this protein was also studied. Water-immersion stress and the administration of 5-HT induced synthesis of HSP60 in rat colonic mucosa. The induction of HSP60 and the number of defecations were clearly inhibited by the oral administration of YM-060. Our results suggest that the induction of HSP60 in rat colonic mucosa by water-immersion stress may be associated with gastrointestinal motility mediated by 5-HT, especially via 5-HT3 receptors.

Cisapride: a gastrointestinal prokinetic drug

OBJECTIVE

To summarize the pharmacology, pharmacokinetics, efficacy, and safety of cisapride, and to evaluate its potential therapeutic role.

DATA SOURCES

A computerized search of the MEDLINE database was used to identify English-language publications of cisapride data in humans. The MEDLINE search was supplemented by review article bibliographies. There was no attempt to limit the search to a specific gastrointestinal motility disorder.

STUDY SELECTION

The MEDLINE search alone identified 165 citations. Because of the volume of available human cisapride data, the focus of the efficacy section is on complete published reports of controlled clinical studies. Abstracts and uncontrolled data are discussed only when other information is unavailable to address important aspects.

DATA EXTRACTION

Information regarding study design, study population, results, and safety was recorded from each publication. The placebo response to gastrointestinal complaints in patients with motility disorders is high. Therefore, objective evidence of improvement was emphasized when documentation was available.

DATA SYNTHESIS

Cisapride stimulates the motility of smooth muscle lining the esophagus, stomach, small intestine, and colon, and increases the tone of gut sphincters in vitro and in vivo. In controlled investigations, cisapride was superior to placebo in relieving symptoms associated with reflux esophagitis, nonulcer dyspepsia, and gastroparesis. Similar symptom and healing effects were observed with cisapride and histamine (H)2-antagonists in reflux esophagitis. Cisapride was either equal to or superior to metoclopramide in relieving reflux symptoms. However, metoclopramide was associated with significantly more central nervous system adverse effects. Cisapride was well tolerated, with adverse effects limited primarily to the gastrointestinal tract.

CONCLUSIONS

Cisapride represents an attractive alternative to metoclopramide for the treatment of a variety of motility disorders. Because it addresses a primary underlying cause of reflux esophagitis, cisapride may also prove to be an effective alternative to acid suppressants in the management of this disorder.

Involvement of neurokinins in the non-cholinergic response to activation of 5-HT3 and 5-HT4 receptors in guinea-pig ileum

1. The involvement of neurokinins in the non-cholinergically-mediated contractile response induced by stimulation of 5-HT3 and 5-HT4 receptors has been examined in the longitudinal muscle-myenteric plexus preparation of the guinea-pig ileum. 2. The 5-HT3 receptor agonist, 2-methyl-5-hydroxytryptamine (2-methyl-5-HT), showed a lower potency in this preparation than the more selective 5-HT4 receptor agonist 5-methoxytryptamine. The effect of both drugs was markedly reduced by atropine. 3. Substance P (SP) and neurokinin B (NKB) produced biphasic concentration-response curves in the preparation. Neurokinin A (NKA), the NK1 receptor agonist, [Sar9,Met(O2)11]SP and the NK3 receptor agonist, senktide yielded monophasic concentration-response curves. 4. After desensitization of the NK1 receptor with SP or [Sar9,met(O2)11]SP, in the presence of atropine, the contractile response to 2-methyl-5-HT was entirely blocked. Desensitization of NK3 receptors with NKB, also in the presence of atropine, fully suppressed the 5-HT4 receptor-mediated contraction evoked by 5-methoxytryptamine. 5. In preparations prelabelled with [3H]-choline, SP produced a concentration-dependent increase in tritium overflow, an index of [3H]-acetylcholine release, while an inverse relationship was found with NKB. At low neurokinin concentrations, the releasing effect of NKB was much more marked. 6. It is suggested that in the response to 5-HT3 receptor stimulation, there is a role for SP and acetylcholine. NKB appears to be preferentially involved in the release of acetylcholine elicited by stimulation of 5-HT4 receptors.

Cisapride. An updated review of its pharmacology and therapeutic efficacy as a prokinetic agent in gastrointestinal motility disorders

Cisapride is an orally administered prokinetic agent which facilitates or restores motility throughout the length of the gastrointestinal tract. It is a substituted piperidinyl benzamide, chemically related to metoclopramide, but unlike metoclopramide, cisapride is largely devoid of central depressant or antidopaminergic effects. In placebo-controlled trials, cisapride improved healing rates and symptoms in both adults and children with reflux oesophagitis. Maintenance therapy with cisapride at half the healing dose is effective in reducing the incidence of relapse. Symptoms are also alleviated in patients with functional dyspepsia, and gastric emptying and symptoms are improved in most patients with gastroparesis, an effect which is sustained during long term administration. However, the efficacy of cisapride in end-stage gastroparesis remains less clear. Cisapride increases stool frequency in patients with chronic constipation, and limited data suggest that the drug may also be beneficial in treating chronic intestinal pseudo-obstruction and irritable bowel syndrome. Cisapride demonstrated efficacy comparable with or superior to that of metoclopramide, and was at least as effective as cimetidine and ranitidine in patients with reflux disease. In patients with functional dyspepsia, cisapride has shown at least equal efficacy to domperidone, metoclopramide and ranitidine, and superior efficacy to cimetidine in the small comparative trials conducted to date. Adverse effects in patients receiving cisapride are generally transient and mild, with abdominal cramping, borborygmi, diarrhoea or loose stools most frequently reported. Central nervous system adverse effects are rare. Thus, with its favourable tolerability profile and demonstrated efficacy in a variety of gastrointestinal motility disorders, the position of cisapride as a valuable agent in the management of patients with gastrointestinal motility disorders is strengthening. However, larger well-controlled comparative trials of the drug with other agents are necessary before the relative position of cisapride in therapy can be categorically defined.

Cisapride versus metoclopramide in the treatment of functional dyspepsia. A double-blind comparative trial

The efficacy and tolerability of cisapride (5 mg three times daily) and metoclopramide (10 mg three times daily) were evaluated in a randomized double-blind trial in patients with functional dyspepsia. Sixty patients, equally distributed in the two groups, entered the trial. After 4 weeks of treatment there was a significant improvement of symptom severity versus base line (p < 0.001) in both groups. The percentage of responders (with no or only mild symptoms) was 87% in the cisapride group and 77% in the metoclopramide group (no statistically significant intergroup difference). At the follow-up visit 2 weeks after completion of the trial this response rate was significantly higher in the cisapride group (73%) than in the metoclopramide group (47%) (p < 0.05). Four of the patients receiving cisapride and 2 of the patients receiving metoclopramide reported adverse events. On assessment of extrapyrimidal symptoms, relevant clinical values were found in one patient receiving metoclopramide. Increased prolactin concentrations were observed in seven patients of the metoclopramide group versus only 1 of the cisapride group (p < 0.05). The present data indicate that during the 2 weeks after completion of treatment in patients with functional dyspepsia, cisapride may result in a better, more sustained overall response when compared with metoclopramide.

Stimulation of formation of cAMP by 5-hydroxytryptamine in myenteric ganglia isolated from guinea pig small intestine

Effects of 5-hydroxytryptamine (5-HT) and related agonists and antagonists on formation of cAMP were determined for enzymatically dissociated ganglia from the myenteric plexus of the guinea-pig small intestine. Formation of cAMP was stimulated by 5-HT in both dose- and time- dependent manners. The stimulatory action of 5-HT was suppressed by the 5-HT1P antagonist, renzapride, but not by the 5-HT3 antagonist, tropisetron (formerly ICS 205-930). Neither renzapride nor cisapride increased the levels of cAMP. Levels of cAMP were suppressed by concentrations of tropisetron greater than 1.0 microM. Levels of cAMP were unaffected by the 5-HT3 agonist, 2-methyl-5-hydroxytryptamine. A putative 5-HT4 receptor agonist, 5-methoxytryptamine, stimulated formation of cAMP, but to a lesser extent than 5-HT. We conclude that 5-HT acts to stimulate adenylate cyclase and the formation of cAMP in myenteric ganglia. The 5-HT1P receptor is the most likely subtype involved in 5-HT action on cAMP formation.

Cisapride and a structural analogue, R 76,186, are 5-hydroxytryptamine4 (5-HT4) receptor agonists on the guinea-pig colon ascendens

The purpose of this study was to investigate whether the effects of cisapride and its close structural analogue R 76,186 on the isolated guinea-pig colon ascendens, are mediated through 5-HT4 receptors. Both cisapride and R 76,186 induced contractions in a concentration-dependent fashion, giving monophasic concentration-response curves (cisapride: EC50 = 1.1 x 10(-7) M, maximum effect = 40.3% of methacholine-induced (3 x 10(-7) M) contractions; R 76,186: EC50 = 2.4 x 10(-8) M, maximum effect = 52.1%). Blockade of either 5-HT2 or 5-HT3 receptors did not affect the responses to cisapride. However, tropisetron (in 5-HT4 receptor-blocking concentrations), and DAU 6285 and SDZ 205-557, two novel selective 5-HT4 receptor antagonists, depressed the concentration-response curve to cisapride (to about 50%), and the curve to R 76,186 was shifted to the right. The apparent pA2 values were 6.6 (tropisetron), 6.3 (DAU 6285), and 7.5 (SDZ 205-557). However, none of these antagonisms was purely competitive as higher concentrations of these antagonists depressed the curve to R 76,186. Desensitization of the 5-HT4 receptor with 5-methoxytryptamine (5-MeOT) inhibited the responses to cisapride, and abolished those to R 76,186. The contractions to cisapride and R 76,186 were sensitive to mutual antagonism, depressing their concentration-response curves.

CONCLUSIONS

Both cisapride and R 76,186 mediate their contractile effects in the guinea-pig colon ascendens through agonism at the 5-HT4 receptor, though cisapride also uses a non-5-HT mechanism. R 76,186 is a selective and potent 5-HT4 receptor agonist.