INHIBITION DE LA RENINE ET EFFET ANTIHYPERTENSEUR DE LA METHYLDOPA

The antihypertensive effect of methyldopa is well known but its mechanism of action is still the subject of debate. The drug may interfere with sympathetic control of arterial pressure or it may exert a renin-inhibiting effect. A recent clinical study has drawn attention to 3 points: Methyldopa lowers blood pressure in the recumbent position and even more so in the standing position. Concomitantly, plasma renin levels also drop proportionally in the recumbent and standing positions. Methyldopa reduces blood pressure to a greater extent than propranolol, particularly in the standing position. Conversely, the secretion of renin in response to the erect position is inhibited to a greater degree by propranolol than by methyldopa. The antihypertensive effect of methyldopa is dose-dependent, whereas its renin inhibiting effect is not; the two effects are therefore independent. Methyldopa lowers plasma renin activity (PRA) only moderately (regardless of the initial level) and hence determination of PRA does not appear to be a useful index for predicting the therapeutic effects of methyldopa.