title: The emetic effect of B-HT 920 and apomorphine in the dog: antagonism by haloperidol.
abstract: Recent investigations have suggested that the alpha 2-adrenoreceptor agonist B-HT 920 is also a dopamine (DA) agonist with a selectivity for presynaptic receptors. In the present study, the emetic effect of B-HT 920 was investigated. Intravenous injections of B-HT 920 (0.32-10.0 micrograms/kg) and a DA2-agonist apomorphine (3.2-100.0 micrograms/kg) caused dose-dependent emesis. The ED50 of B-HT 920 and apomorphine were 3.2 and 12.3 micrograms/kg, respectively. When haloperidol (10.0-24.5 micrograms/kg i.v.), a DA2-antagonist, was given 5 minutes before B-HT 920 (10 micrograms/kg) or apomorphine (32 micrograms/kg), it caused a dose-dependent prevention of B-HT 920- and apomorphine-induced emesis. The ED50 of haloperidol in preventing the emetic effect of both drugs was identical (13.5 micrograms/kg). In contrast, haloperidol (32 micrograms/kg i.v.) did not prevent the emetic effect of ouabain (40 micrograms/kg i.v.). Neither did yohimbine (0.1 mg/kg i.v.), an alpha 2-adrenoreceptor antagonist, prevent the emetic effect of B-HT 920 (10 micrograms/kg). These results suggest that B-HT 920, acting like apomorphine, induces emesis by activating DA2-receptors probably in the chemoreceptor trigger zone of the area postrema.
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000037:antagonists & inhibitors*; D000818:Animals; D001058:Apomorphine / Q000037:antagonists & inhibitors*; D001381:Azepines / Q000037:antagonists & inhibitors*; D004285:Dogs; D004639:Emetics; D006220:Haloperidol / Q000494:pharmacology*; D010042:Ouabain / Q000037:antagonists & inhibitors; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D001381:Azepines; D004639:Emetics; D015016:Yohimbine; D010042:Ouabain; C024763:talipexole; D006220:Haloperidol; D001058:Apomorphine