Fluphenazine, ICS 205-930 and dl-fenfluramine differentially antagonise drug-induced emesis in the ferret.

The intravenous injection of cisplatin (10 mg/kg), the subcutaneous injection of apomorphine (0.125-1 mg/kg) and lisuride (0.001-0.1 mg/kg), the oral administration of ipecacuanha (0.3-2.4 mg/kg) and the intragastric administration of copper sulphate (25-100 mg/kg), induced a vomiting and retching response in the ferret. Pretreatment with dl-fenfluramine (5 mg/kg i.p.) prevented or reduced the emesis induced by cisplatin, apomorphine, ipecacuanha and lisuride but failed to significantly antagonise copper sulphate-induced emesis. The 5-HT3 receptor antagonist ICS 205-930 (0.1 mg/kg i.p.) prevented emesis induced by cisplatin and ipecacuanha but failed to prevent or significantly reduce the emesis induced by apomorphine, lisuride or copper sulphate. Dopamine receptor antagonists, including fluphenazine (0.1-1.0 mg/kg i.p.) prevented apomorphine- and lisuride-induced emesis but were less potent or had inconsistent actions to antagonise cisplatin- or ipecacuanha-induced emesis and failed to inhibit the emesis induced by copper sulphate. The data indicate that dopamine and/or 5-HT3 receptor systems are involved in drug-induced emesis but that emesis caused by gastric irritation induced by copper sulphate is mediated by different receptor mechanisms.

The action of dazopride to enhance gastric emptying and block emesis.

The substituted benzamide derivatives, dazopride and metoclopramide, enhanced field stimulation-induced contractions of guinea-pig stomach strips and gastric emptying in the guinea-pig after peripheral, intracerebroventricular and intrahypothalamic injection. In the isolated vagal nerve preparation from the rabbit, both compounds were shown to be 5-hydroxytryptamine M-receptor antagonists. Dazopride and metoclopramide were equipotent in antagonising cisplatin-induced emesis in the ferret, whereas metoclopramide was approximately 200 times more potent than dazopride in antagonising the emesis caused by the dopamine agonist 2-di-n-propylamino-5,6-dihydroxytetralin in the marmoset. In behavioural tests which indicate dopamine receptor antagonism in the rat, metoclopramide induced catalepsy, antagonised amphetamine-induced stereotypy and the hyperactivity induced by the intrastriatal injection of dopamine, caused body asymmetry on unilateral injection into the striatum and also antagonised apomorphine-induced climbing and circling behaviour in the mouse. In contrast, dazopride had little or no action in these tests and failed to displace [3H]spiperone in radioligand binding assays. The use of dazopride provides evidence to dissociate a dopamine receptor blockade from an ability to facilitate gastric emptying and to antagonise cisplatin-emesis, and indicates that antagonism of 5-hydroxytryptamine M-receptors is the essential basis of action for dazopride and plays an important role in the actions of metoclopramide.

Zacopride, a potent 5-HT3 antagonist.

The substituted benzamide derivative zacopride was found to antagonize competitively the effects of 5-hydroxytryptamine (5-HT) on the guinea-pig ileum, the rabbit vagus nerve and the von Bezold Jarisch reflex in the rat. The potency of zacopride was comparable with that of ICS 205-930 and it is concluded that zacopride possesses 5-HT3 receptor antagonizing properties.

Characterization and partial purification of human monoamine oxidase-B expressed in Escherichia coli.

Monoamine oxidases (MAO-A and MAO-B) are enzymes that play a key role in the degradation of endogenous and dietary monoamines. A full-length cDNA of the B-type of MAO, isolated from a human liver cDNA library, was cloned into a prokaryotic expression vector (pET11c). Escherichia coli which was transfected with the recombinant plasmid expressed an insoluble protein product with the expected molecular weight (65 kDa). However, in the inclusion body fraction, where most of the recombinant protein was present, no MAO activity was observed. In contrast, the membrane fraction of the bacterial lysates expressed catalytic activity as estimated by oxidative deamination of beta-phenylethylamine and tyramine. The active enzyme protein was solubilized with Triton X-100 and partly purified (80-fold) on a DEAE-Sepharose column. This enzyme activity showed properties very similar to those of human brain and platelet MAO-B. Moreover, a single band of the expected molecular size was observed on an immunoblot. The peak fraction from the DEAE-Sepharose separation was further purified on a tyramine-Sepharose column, yielding a highly purified enzyme (190-fold), visible as a band on a sodium dodecyl sulfate-containing polyacrylamide gel.