1. The immediate short-term effects of intravenous injections of propranolol on plasma renin activity were studied in thirty-one normal subjects, 102 patients with benign essential and sixty-six patients with renal hypertension.

2. In essential hypertensive patients and normal subjects a marked fall in plasma renin activity was observed within 15 min, which was directly proportional to initial plasma renin values. In contrast, in patients with renal hypertension the fall observed was much less pronounced, or totally absent.

3. These differences in response to propranolol, which were particularly pronounced in patients with high initial renin values, suggest a dominant role of sympathetic tone at the juxtaglomerular apparatus for basal renin release in normal individuals and essential hypertensive subjects only.

4. The observations also indicate that sympathetic activity plays no part in the control of basal renin secretion in patients with renal hypertension, in whom basal renin secretion may be maintained by the renal baroreceptors.

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