1. In 11 patients with uncomplicated essential hypertension in whom renal arteriography had been carried out, arterial and venous samples were drawn for determination of active renin, angiotensin II and catecholamines, both before and after 3 min of static exercise (handgrip).
2. In five patients the experiment was continued by administration of phentolamine (5 μg min−1 kg−1) into the renal artery. During this procedure blood samples were drawn again before and after handgrip exercise. At all times renal plasma flow was measured from the clearance and extraction of [125I]hippuran.
3. At rest the kidney secreted renin and noradrenaline, and angiotensin II and adrenaline were extracted from the circulation. During static exercise secretion of renin and noradrenaline was enhanced, and extraction efficiency for angiotensin II and adrenaline was reduced. During infusion of phentolamine similar patterns were found for renin and catecholamines, but the pattern for angiotensin II was reversed.
4. It is concluded that sympathetic activity in the kidney and perhaps also the absolute level of renal blood flow determine the renal extraction efficiency for angiotensin II. Reduced uptake of angiotensin II by an α-adrenergic mechanism may protect the kidney from excessive vasoconstriction.