STUDIES ON THE HYPOTENSIVE ACTION OF α‐METHYLDOPAMINE

Abstract

1 Intraventricular α-methyldopamine (50–200 μg) produced a dose-related fall in blood pressure in conscious spontaneously hypertensive rats. Pretreatment with intraventricular 6-hydroxydopamine prevented this hypotensive effect of α-methyldopamine. 2 The hypotensive effect of α-methyldopamine was prevented by intraventricular injection of phentolamine or desmethylimipramine, but not by intraperitoneal injection of haloperidol. 3 Pretreatment with U-14,624, a selective central dopamine-β-hydroxylase inhibitor, prevented the hypotensive effect of α-methyldopamine. 4 α-Methyldopamine was considerably less potent than noradrenaline as a pressor agent in the pithed rat, but noradrenaline and α-methylnoradrenaline were found to be equipotent. 5 α-Methyldopamine (1–5 mg i.c.v.) reduced pressor responses elicited by electrical stimulation of the mid brain reticular formation in cats anaesthetized with chloralose. 6 It is concluded that the hypotensive action of α-methyldopamine in conscious animals involves intact central α-adrenergic neurones and a central adrenergic uptake mechanism for the formation of α-methylnoradrenaline.