?-Adrenergic Blockade in Essential Hypertension Reduced Renin Release Despite Renal Vasoconstriction

The acute effects of small doses of intravenous propranolol on renin release and on circulatory dynamics were studied at the time of renal arteriography in 12 persons with essential hypertension. All of the subjects had a normal peripheral renin response to chronic sodium depletion and all had normal renal function. Seven subjects received a 10-mEq sodium diet for at least 4 days prior to study and five received a 200-mEq sodium diet. At the time of arteriography, arterial blood pressure, pulse rate, cardiac output, renal blood flow, and arterial and renal venous renin activity were measured before and 6-20 minutes after the intravenous administration of propranolol (9-18 jtg/kg). Average renin secretion rate in the salt-depleted subjects fell from 367 ± 80 (SEM) U/ml per 100 g/min to 122 ± 51 U/ml per 100 g/min (/> _ 0.03), and renal plasma flow fell from 189 to 155 ml/min per 100 g (P 0.018). We also found that in the salt-loaded subjects, renal plasma flow fell from 213 to 184 ml/min per 100 g (P 0.025), whereas renin secretion did not change significantly. Furthermore we found that mean arterial pressure and cardiac index did not change significantly in either group. We conclude that propranolol rapidly blocks renin release despite circulatory changes which ordinarily constitute a stimulus for renin secretion, i.e., renal vasoconstriction and reduced renal blood flow.