Observations of the role of body fluid volumes and plasma renin activity in the management of hypertension.

Reduction of the (expanded) body fluid volumes found in some patients with renal hypertension may be essential in the management of these cases. Illustrative examples are given of this "volume dependent" form of hypertension. In such patients, plasma renin activity (PRA) is low. Other forms of hypertension may be regarded as caused by "inappropriate renin secretion". Most often, however, both factors are operative. This concept is supported by experimental evidence obtained in animals. The combined effect of salt depletion (which increases PRA) and beta-adrenergic blockade with propranolol (during which treatment PRA is lowered) was systematically studied in 3 groups of hypertensive patients (including one group with chronic renal insufficiency). The results indicate that this combined therapy lowers the blood pressure in various types of hypertension, the effect being sometimes more than additive. There was, however, no correlation between the PRA levels and the blood pressure decrease after salt depletion or after propranolol. Consequently, on the basis of the PRA values, no group of patients could be identified for which this treatment would be specifically indicated.