Question

The turbulent blood flow through the renal artery, narrowed due to atherosclerosis, led to the sound detected upon examination. Why did the differential renal vein renin test show an increased in the blocked renal artery side secretion of renin, yet a drop in renin levels on the other (normal) side?

Answer 1

All four factors which theoretically may affect the renal vein renin ratio in unilateral renal artery stenosis--increased renin secretion and diminished renal plasma flow on the stenotic side; suppressed renin secretion and renin extraction on the contralateral side--have been assessed. In a series of patients with unilateral renal artery stenosis, the renal vein ratio of active renin was more closely related to the reduction of renal plasma flow than to renin secretion rate on the affected side. On the contralateral side renin secretion was suppressed while angiotensin II was extracted. During long-term treatment with the converting enzyme inhibitor enalapril, peripheral plasma angiotensin II was lowered, while active renin concentration was markedly elevated, both in arterial plasma and in renal venous plasma of the stenotic kidney; the contralateral kidney became a net extractor of active renin. Thus, all 4 factors which theoretically affect the renal vein renin ratio can operate clinically. Both before and during enalapril, the affected kidney secreted inactive renin.