The importance of renal vascular tone in determining the severity of renal artery stenosis in dogs.

1. The effects of the state of renal vascular tone during induction of renal artery stenosis on the subsequent systemic blood pressure and renin responses have been studied in chronically instrumented, conscious dogs. 2. In one group of dogs, renal vascular tone was altered by brief (2-3 min) renal artery infusions of ACh, saline, methoxamine or angiotensin II during narrowing of the renal artery to reduce distal pressure to 40 mmHg. The infusions were turned off 1 min later. 3. The more vasoconstricted the kidney at the time of stenosis, the slower was the restoration of distal renal artery pressure and the greater the rises in systemic blood pressure, plasma renin activity (PRA) and effective stenosis resistance. At the end of 1 hr of stenosis, the rises in systemic blood pressure were 4.3 +/- 3.3, 11.3 +/- 3.3, 28.9 +/- 3.3 and 26.3 +/- 2.8 mmHg for the ACh, saline, methoxamine and angiotensin II-infused dogs respectively; rises in PRA were 0.3 +/- 0.24, 1.18 +/- 0.42, 5.09 +/- 1.38 and 4.02 +/- 0.74 ng/ml. per hr respectively. 4. In another group of dogs a given aortic-renal artery pressure gradient was produced on two occasions: (i) with the animal conscious; (ii) under brief sodium pentobarbitone anaesthesia and preparation for surgery. After 24 hr systemic blood pressure had risen by 15.7 +/- 3.6 mmHg above initial values when stenosis was induced under anaesthesia (P < 0.05) and only by 1.2 +/- 3.6 mmHg (N.S.) when it was induced with the animal conscious. Corresponding rises in PRA were 1.29 +/- 0.42 (P < 0.05) and 0.25 +/- 0.11 (N.S.) ng/ml. per hr. Establishment of a given gradient in the high vascular resistance kidney of the anaesthetized dog thus requires greater narrowing of the renal artery than in the lower resistance renal bed of the conscious animal. 5. The tone of the renal vascular bed is a major determinant of the severity of renal artery stenosis.