Changes in regional hemodynamics and function of the kidney during inhibition of angiotensin converting enzyme were studied in 25 patients with renovascular hypertension. A variety of patterns were observed depending upon (1) the activity of the renin-angiotensin system and concomitant administration of diuretics, and (2) the presence of bilateral renal artery stenosis. Increase in blood flow, glomerular filtration rate and sodium excretion during angiotensin blockade, in some instances, indicated tonic renal vasoconstriction before therapy. Release of the kidney from these effects may explain, in part, the sustained effectiveness of converting enzyme inhibition in chronic congestive heart failure. When compared with blood pressure reduction due to nitroprusside administration, initial captopril therapy in patients with unilateral stenosis produced a selective decrease in glomerular filtration, despite well-preserved renal blood flow. These results confirm the importance of efferent arteriolar vasoconstriction due to angiotensin II in man. Experimental studies demonstrate that angiotensin may become critical to sustaining glomerular filtration rate in the presence of stenosis during vasodilation. In patients with bilateral stenosis, this effect produces a syndrome of functional renal insufficiency. Taken together, these data demonstrate an intrarenal action of angiotensin II in human renovascular hypertension and underscore the importance of evaluating the functional impact of changes in regional hemodynamics.
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