The intrarenal pressure distal to the stenosis should be lower than the arterial pressure. As a result, lowering systemic blood pressure will further reduce intrarenal pressure to below normal. Nevertheless, autoregulation will maintain GFR unless the stenosis is so severe or the systemic pressure is lowered so much that intraglomerular pressure falls below the autoregulatory range. The administration of an angiotensin-converting enzyme inhibitor will tend to lower GFR by blocking angiotensin II–mediated regulation at the efferent arteriole. Therefore, the combination of reduced afferent flow distal to the stenosis and inhibition of normal efferent regulatory mechanisms by angiotensin-converting enzyme inhibitor can lead to acute renal failure (if bilateral renal artery stenoses or unilateral stenosis in a solitary kidney).