No evidence for central histamine-receptor involvement with the hypotensive effect of clonidine in cats

Abstract

In conscious hypertensive cats, intraventricular (i.c.v.) administration of clonidine (25 μg), induced hypotension and bradycardia. Pretreatment with metiamide (2 mg i.c.v.) did not significantly antagonise either the hypotension or bradycardia induced by clonidine (25 μg), but induced marked behavioural changes. Central pretreatment with mepyramine (200 μg, i.c.v.) or procaine (600 μg i.c.v.), reduced the hypotension evoked by clonidine (25 μg), but no antagonism of the clonidine-induced bradycardia was apparent. Central phentolamine (200 μg, i.c.v.) or tolazoline (200 μg, i.c.v.) antagonised the hypotension and bradycardia evoked by i.c.v. clonidine.