In order to clarify the properties of sympathetic nerve activity in low renin essential hypertension, plasma catecholamines (CA), dopamines-hydroxylase (DBH) activity and urinary CA were measured and the changes of these variables induced by 60 head-up tilt or i.v. injection of tyramine (0.1 mg/kg) were also measured in in-patients with low renin (LRH) and normal renin essential hypertension (NRH). In addition, blood pressor response to tyramine, i.v. infusion of 0.3 µg/kg/min. of noradrenaline (NA Response) and 0.015 µg/ kg/min. of angiotensin-II (ANG-II Response) were determined before and after salt restriction (Na 35, K 75 mEq) for 7 days or salt loading (Na 390, K 75 mEq) for 14 days. The basal values of plasma noradrenaline (NA), plasma DBH, and 24 hour urinary excretion of NA in LRH were significantly lower than in either NRH (p<0.01, 0.05 and 0.01, respectively) or normotensive subjects (p < 0.05, 0.05 and 0.001, respectively). Plasma NA, plasma DBH and urinary output of NA clearly rose after 30 min. to two hours of the tilt in both LRH and NRH, and the maximal values of plasma NA [formula omitted] during tilting was significantly lower in LRH compared with those in NRH, while no significant difference was observed in the changes of plasma DBH and urinary NA between LRH and NRH. Following i.v. injection of tyramine, the maximal value of plasma NA and blood pressure rise was significantly lower [formula omitted] and significantly higher [formula omitted] than those in NRH, respectively. Following salt restriction, significant reduction of mean arterial pressure (MAP), pressor response to NA and ANG-II and a marked augmentation of PRA and urinary NA were observed. LRH showed a more marked reduction of MAP [formula omitted] and of NA Response [formula omitted] and a significantly higher augmentation of urinary NA excretion [formula omitted] than those in NRH. The increase of PRA [formula omitted] and the decrease of ANG-II Response [formula omitted] were less in LRH than in NRH. On the other hand, following salt loading, LRH exhibited a significant elevation of MAP and diminution of urinary NA, which differed markedly [formula omitted] from those in NRH, in whom no significant changes were observed. No significant difference was observed between LRH and NRH in the other variables. These findings suggest that, in LRH, there exists a reduced sympathetic nerve activity at rest and a suppressed sympathetic responsiveness to the postual and tyramine stimulation, and these reduced sympathetic activity might be not primary but rather secondary to the changes in water-sodium balance. © 1979, The Japanese Circulation Society. All rights reserved.
