Diuretics, Sodium Intake, and Renin in the Management of Hypertension

Twenty-four-hour urinary sodium excretion and plasma renin activity were monitored in 36 patients receiving bendrofluazide as sole antihypertensive therapy. There was no increase in urinary sodium output compared with pretreatment values during a 2-year period, and there is therefore no evidence that an increase in salt appetite as a result of salt depletion occurred. However, plasma renin activity progressively increased over a 2-year period. In five of eight patients who initially had a subnormal renin response to the diuretic, plasma renin level rose into the normal stimulated range. When administration of the diuretic was stopped in 10 patients after a mean treatment period of 49 months, plasma renin activity promptly fell and weight increased significantly, although blood pressure did not rise. However, on rechallenging with bendrofluazide 28 days later, a greater response was observed than when treatment was originally instituted. Further, three of five patients with low renin hypertension had a normal response on the second occasion. Thus prolonged diuretic therapy has a persistent effect on the activity of the renin-angiotensin system as well as on blood pressure for at least 4 weeks after the discontinuation of diuretics.