Behaviors of sympathetic and renin-angiotensin-aldosterone systems to an acute sublingual administration of nifedipine (10 mg) were studied in essential hypertensive (EHT) and normotensive (NT) groups. Basal values of plasma norepinephrine (NE) and plasma renin activity (PRA) were not consistent with mean blood pressure (BP), indicating no important role of NE and PRA values for determining BP level.
Nifedipine reduced BP, and increased NE and PRA in both groups. Simultaneously, nifedipine produced a significant decrease of plasma aldosterone concentration (PAC) and plasma cortisol. High-renin EHT subgroup showed greater responses of BP, NE and PRA than normal- or low-renin subgroup but not in NT group. In high-, normal- and low-renin subgroups of both groups, the correlations between mean BP and △mean BP (r= -0.85, p<0.001; r= -0.89, p<0.001 and r= -0.77, p<0.001, respectively), △mean BP and △NE (r= -0.76, p<0.01; r= -0.71, p<0.05 and r= -0.57, NS, respectively) and △mean BP and △PRA (r= -0.87, p<0.001; r=0.59, NS and r= -0.05, NS, respectively) were observed. A significant relationship between basal PRA and △PRA was demonstrated in EHT group (r=0.77, p<0.001) but not in NT group (r=0.37, NS).
These data indicate the presence of high vascular tone in high-renin EHT subgroup which is probably produced by an increased vascular responsiveness to sympathetic and/or to angiotensin II or by some other factors. It is suspected that juxtaglomerular cell response to vasodilator may be altered in patients with low-renin essential hypertension. The present study also suggests that nifedipine blocked aldosterone and cortisol secretion through Ca++ influx inhibition into the adrenal cortex
