[Experimental study of the hypotensive effect of apomorphine].

The effects of central (intracisternal: i.c.) and peripheral (intravenous: i.v.) administration of apomorphine (200 micrograms/kg) were compared in chloralose anaesthetized dogs. I.v. or i.c. apomorphine induced a decrease in blood pressure (BP) and an increase in heart rate (HR). However, the decrease in BP was more marked after i.c. route. This effect was due to an activation of presynaptic dopaminergic receptors since it is suppressed by i.v. haloperidol of i.v. phentolamine. I.v. atropine abolished the induced-tachycardia. I.v. but not i.c. domperidone suppressed the hypotensive response to i.v. or i.c. apomorphine. The decrease in BP induced by apomorphine was not found in dogs deprived of adrenal medulla. These results confirm the hypotensive properties of apomorphine and suggest the involvement of peripheral dopaminergic mechanisms in this effect. Dopaminergic agonists may represent a new class of antihypertensive drugs.