Enhancement of renal venous renin ratios by intravenous hydralazine in renovascular hypertension.

Renal venous renin (RVR) studies were done in 34 patients with moderate-to-severe hypertension before (unstimulated) and after (15- and 30-minute samples) a 20-mg bolus of i.v. hydralazine. The unstimulated lateralizing ratio of angiographically abnormal kidney or ipsilateral (I) to contralateral (C) RVR of greater than or equal to 1.5 was found in 69%, and the unstimulated ratio of I-inferior vena cava (IVC) renin below renal veins (I-IVC)/IVC (index of reduced renal blood flow) of greater than or equal to 0.48 was present in 50% of 16 patients (10 unilateral and 6 bilateral renal artery stenosis). The I/C and I-IVC/IVC ratios were abnormal in 100% and 88%, respectively, in 1 or both of the posthydralazine sampling in these patients. Hydralazine increased the absolute RVR from the ischemic kidney more than the contralateral kidney and did not result in new false-negative or positive I/C ratios. It is concluded that hydralazine stimulation of RVR is a safe and reliable way to determine the functionally significant pressor kidney in renovascular hypertension.