The plasma noradrenaline and growth hormone response to alpha-methyldopa and clonidine in hypertensive subjects.

The mechanism of the antihypertensive effect of alpha-methyldopa was compared with clonidine by administering equipotent single doses of clonidine (0.2 mg) and alpha-methyldopa (750 mg) to nine hypertensive patients. Plasma noradrenaline was followed for 8 h thereafter as an index of peripheral sympathetic activity. alpha-Methyldopa and clonidine produced the same hypotensive response at 6 and 8 h after dosing with a similar fall in plasma noradrenaline levels at these times. Linear regression analysis between the systolic blood pressure fall and the corresponding plasma noradrenaline fall, showed that the slopes of the two regression lines were similar for alpha-methyldopa as for clonidine. Equipotent doses of alpha-methyldopa and clonidine produce the same fall in plasma noradrenaline. This supports the current hypothesis that an alpha-methyldopa metabolite acts centrally, like clonidine, to reduce peripheral sympathetic activity.