The cardiovascular effects of intraventricular clonidine and Bay 1470 in conscious hypertensive cats.

1 Intraventricular administration of clonidine (5-30 mug) and an analogue, BAY 1470 (15-30 mug) to conscious renal hypertensive cats produced a fall in mean blood pressure lasting for approximately 3 hours. This fall in blood pressure was accompanied by a marked bradycardia.2 Pretreatment with intraventricular phentolamine (100-200 mug), piperoxan (40-200 mug) or tolazoline (75-200 mug) abolished the cardiovascular effects of intraventricular clonidine (20 mug).3 The cardiovascular effects of intraventricular clonidine (20 mug) were not modified by the pretreatment with either haloperidol (1 mg/kg i.p.) or desmethylimipramine (1 mg/kg i.p.).4 Emesis was observed 1-2 min after the administration of either clonidine (5-20 mug) or BAY 1470 (30 mug). This preceded the cardiovascular actions and was still seen after pretreatment with haloperidol, desmethylimipramine, phentolamine, piperoxan or tolazoline.5 It is concluded that the centrally mediated cardiovascular responses observed after intraventricular administration of small doses of clonidine are due to stimulation of central alpha-adrenoceptors and are independent of central catecholamine uptake mechanisms and dopamine receptors.