Effect of oral clonidine on human cardiovascular responsiveness: a possible explanation of the therapeutic action of the drug in menopausal flushing and migraine.

The effect of an alpha-adrenergic agonist, clonidine hydrochloride, on cardiovascular responses to noradrenaline, adrenaline and angiotensin was investigated in menopausal women with hot flushes. The increase in forearm blood flow induced by adrenaline, noradrenaline or angiotensin was significantly less in women treated for at least 6 weeks with clonidine compared with that induced in the women by infusions given before treatment. Pulse rate during the amine infusions was significantly lower after clonidine treatment but constrictor responses in the hand were unchanged. These findings cannot be wholly explained in terms of an action of clonidine confined to adrenergic mechanisms and suggest that the drug may influence peripheral vascular responsiveness. Such an effect could explain the mechanism of the beneficial clinical action of the drug in subjects with menopausal flushing or migraine.