R 50 595, a selective non-competitive antagonist of cisapride, BRL 24924 and 5-hydroxytryptamine on the guinea-pig ileum

Nizatidine and cisapride enhance salivary secretion in humans

BACKGROUND

Salivation plays an important role in the defence of the oesophageal mucosa against gastric acidic reflux and can be evoked by cholinergic stimulation. Both nizatidine and cisapride have been reported to increase acetylcholine concentrations in the cholinergic system.

AIM

To investigate the effect of nizatidine and cisapride on salivary secretion, salivary epidermal growth factor and bicarbonate output.

METHODS

The salivary volume and concentration of salivary epidermal growth factor and bicarbonate were measured after the administration of nizatidine (150 mg), famotidine (20 mg) and cisapride (5 mg) in 30 male healthy volunteers.

RESULTS

Basal and stimulated salivary secretions were found to be increased after the administration of nizatidine and cisapride. In contrast, salivary secretion was not increased by famotidine. Although epidermal growth factor content was not augmented, nizatidine and cisapride administration also increased the bicarbonate output in mastication-stimulated saliva.

CONCLUSIONS

Increased salivary secretion and bicarbonate output induced by nizatidine may be useful for the treatment of patients with gastro-oesophageal reflux disease.

Excitation and inhibition by cisapride of spontaneous and evoked electrical responses in smooth muscles of guinea-pig stomach

In isolated circular smooth muscles of the guinea-pig stomach, cisapride depolarized the membrane, increased the amplitude and interval of slow waves, and enhanced the cholinergic excitatory junction potential, with no change in the nonadrenergic noncholinergic inhibitory junction potentials. Methysergide mimicked the excitatory actions of cisapride on junction potentials. Results showed that cisapride has dual actions on gastric muscles; excitation by facilitating the release of ACh possibly via 5-HT receptor blockade and also by depolarizing the smooth muscle membrane, and inhibition by reducing the frequency of slow waves, possibly by acting directly on the pacemakers.

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

It has been suggested that benzamides, like cisapride, exert their effects on the guinea-pig ileum via activation of a 5-HT receptor (5-HT4 receptor?) mechanism. The aim of this study was to determine whether an how the 5-HT4 receptor (previously described in mouse colliculi neurones) is involved in the cisapride-induced effect. The effects induced by cisapride were compared with those of 5-hydroxytryptamine (5-HT) and 5-methoxytryptamine (5-MeOT) either alone or in the presence of a 5-HT4 antagonist (micromolar concentration of ICS 205-930) or a benzamide antagonist (R 50 595). As a model we used the electrically stimulated longitudinal muscle myenteric plexus preparation from the guinea-pig ileum. Cisapride (3.10(-7) M), 5-HT and a 5-HT4 receptor agonist 5-MeOT (3.10(-10)-10(-6) M) induced similar effects, i.e. enhancement of the twitch responses. After rinsing the organ baths, a second addition of the agonists resulted in a similar response. The studied agonists showed mutual desensitization. Cisapride desensitized the response induced by 5-HT or 5-MeOT, and 5-MeOT or 5-HT desensitized the effect induced by cisapride. In preparations preincubated with a 5-HT4 receptor antagonist, ICS 205-930- (3.10(-6) M) or R 50 595 (3.10(-7) M), a benzamide with a specific antagonistic action on the effect induced by 5-HT and benzamides on the guinea-pig ileum, the effects induced by cisapride, 5-HT and 5-MeOT were abolished. These results indicate that cisapride indeed exerts its effect via an agonistic action on a serotonin receptor, probably the previously described 5-HT4 receptor.