[Effect of prolonged hydrochlorothiazide administration on the plasma renin activity and aldosterone excretion rate in normal persons]

Body fluid volumes and the response of renin and aldosterone to short- and long-term thiazide therapy of essential hypertension

Plasma volume (PV), extracellular fluid volume (ECV) serum electrolytes, renin and aldosterone were measured before and after 1 week and 4 months of hydrochlorothiazide (HCT) treatment, 50 mg twice daily, in nine male patients with uncomplicated essential hypertension. All studies were carried out under strictly standardized conditions in a metabolic ward. After 1 week of HCT treatment, significant reductions were found in PV and ECV, but after 4 months only ECV was significantly reduced. During HCT therapy, renin and aldosterone were permanently elevated whereas serum sodium and potassium were lowered. After 1 week, renin was inversely correlated with PV and ECV and directly correlated with heart rate. After 4 months, renin was inversely correlated with serum sodium. These results indicate a permanent decrease in ECV during long-term HCT therapy. It is further suggested that the mechanisms responsible for the renin response during short- and long-term HCT treatment are different, changes in body fluid volumes and increased neural activity being responsible for the initial rise in renin, and serum sodium being the predominant factor during chronic treatment.

Plasma renin activity in patients with coarctation of the aorta. A comment of the pathogenesis prestenotic hypertension

In 10 patients with coarctation of the aorta, plasma renin activity was measured after recumbency and orthostatism in peripheral venous blood and, in some cases, in renal venous blood also. In nine of these patients, basic plasma renin values and those obtained under stimulatory conditions lay within normal range, and only in one patient were the values elevated. However, since this patient displayed the lowest gradient of mean arterial blood pressure proximal and distal to the stenosis, it can be regarded as improbable that the elevation in plasma renin activity was caused by the coarctation. Plasma renin activity in the renal venous blood of both kidneys, which was measured in three patients, showed no elevation.

On the basis of observations of other authors and of our own studies it can be concluded that the kidneys can contribute to the development of prestenotic hypertension in acute constriction of the aorta in experiments with animals, but in chronic coarctation in animals or in man the humoral or renal theory has no importance to the pathogenesis of hypertension.