Plasma renin activity in renovascular hypertension

Pre- and postoperative studies in 72 hypertensive patients with renal artery stenosis, with special reference to renin activity and aldosterone

Seventy-two patients, aged 6-69 years, were operated on because of presumed renovascular hypertension and subjected to follow-up studies for 4-60 months (mean 28). Unilateral renal artery stenosis was present in 47 patients. Surgery was followed by normalization of blood pressure (BP) in 28 and improvement in 7, whereas 12 showed no response. Sixteen were below the age of 40 and only one failed to respond to surgery. Peripheral venous plasma renin activity (PRA) was increased in 32 and urinary aldosterone elevated in 22 of 35 patients responding favourably to surgery. Renal vein PRA was higher from the kidney with the stenotic renal artery as compared to the contralateral side in all patients responding to surgery. Preoperative peripheral PRA difference was also found in 7 of 12 patients not responding to surgery. Preoperative peripheral PRA was increased in 26 of the patients becoming normotensive after surgery. In 20 of these patients normalization of BP was associated with a fall in peripheral PR. Twenty-five patients had bilateral renal artery stenosis. Four of them had severe hypertension, renal insufficiency and generalized atherosclerosis. They died in immediate connection with operation. Unilateral operation, performed in 11 of the remaining 21 patients, was followed by normalization of BP in 3 and no response in 8. Bilateral reconstructive surgery, performed in 10 patients, resulted in normotension in 2 and improvement in 7. Our studies indicate that determination of peripheral PRA and/or urinary aldosterone can serve as a useful prognostic indicator after surgery in hypertensive patients with renal artery stenosis.

The hunt for renal hypertension

The proportion of cases of hypertension with a renal cause which can be corrected by surgery is very small. Radiological diagnosis of such a cause is expensive and time-consuming; hence the rewards of intensive investigation are small compared with the cost. Measurement of plasma-renin offers a good method of selecting those patients who require further investigation, if the cut-off point is carefully considered in the light of the acceptable incidence of false-positive and false-negative results.

Hypertension with renal arterial stenosis: humoral, hemodynamic and histopathologic factors

In 46 hypertensive patients with unilateral renal arterial stenosis, peripheral and renal venous plasma renin activity, juxtaglomerular cell count and granularity and systolic pressure gradient across the stenosis were determined. After corrective surgery and a mean postoperative observation period of 4.3 years, 18 patients were completely relieved of hypertension (good responders), 14 had a substantial reduction in arterial pressure (fair responders) and 14 remained hypertensive (poor responders). Analysis of plasma renin activity in both renal veins indicated that a ratio (stenotic/nonstenotic side) greater than 2.0 correctly predicted a favorable surgical result in all cases. Peripheral plasma renin activity was greater than normal in 65 percent of good responders, in 50 percent of fair responders and in one nonresponder. The prognostic accuracy of a pressure gradient greater than 40 mm Hg was 78 percent; no patient with a gradient of less than 40 mm Hg benefited from surgery. An increased juxtaglomerular cell count on the affected side predicted a successful operative result in 88 percent, as did increased granularity in 85 percent of cases. Renal venous renin ratio correlated positively (r =0.738, P less than 0.001) with the pressure gradient across the stenosis. The renal venous plasma renin activity of the affected side also correlated positively (r = 0.771, P less than 0.001) with the absolute count of granular cells in the juxtaglomerular apparatus. Plasma renin activity in both renal veins is the most reliable predictor of operative outcome. The addition of juxtaglomerular cell count or pressure gradient across the stenosis increases prognostic accuracy only slightly. The close mutual correlations between renal venous renin ratio, pressure gradient and juxtaglomerular cell count support the experimental evidence of a causal relation between the hemodynamic effects of the arterial lesion and the humoral and histologic changes observed in hypertension with renal arterial stenosis.

The renin axis and vasoconstriction volume analysis for understanding and treating renovascular and renal hypertension

Information defining the renin-angiotension-aldosterone axis as a control system concurrently regulating salt balance and blood pressure has been applied to reexamine the role of renin in experimental and clinical forms of renovascular and renal hypertension, and thence to develop criteria for differentiating these entities. Experimentally, there are two models of renovascular hypertension; one is characterized by excess renin with reduced sodium (vasoconstrictor form) and the other by excess sodium with reduced renin (volume form). But with sodium depletion, the volume form converts to a vasoconstrictor form illustrating how the two factors coordinate to maintain blood pressure. In man, renovascular and renal hypertensions appear to be sustained by the same two mechanisms. Studies in man show that, in the absence of unilateral disease, the supine renal venous renin level in each kidney is consistently 24 percent higher than the peripheral level. Because of this constant relationship, the peripheral renin level is a measure of the renal secretion rate. Our studies indicate the curable unilateral renovascular hypertension is, in fact, renin-dependent vasoconstrictor hypertension. Three criteria, derived from four renin measurements, identify this situation: (1) Hypersecretion of renin is reflected by a high peripheral level when indexed against sodium excretion. (2) Lateralization of renin secretion with contralateral suppression rules out occult bilateral disease. It is indicated by V-A equal 0 from the uninvolved kidney. (3) (V-A)/A greater than 48 per cent from the ipsilateral kidney supports unilateralization. With data derived from patients with essential hypertension as a reference, the degree to which (V-A)/A is greater than 0.48 can be used to estimate the degree of renal ischemia, using Fick's principle. Corroborative evidence to support these three criteria can be developed from the blood pressure response to angiotensin blocking drugs or to antirenin therapy with propranolol. Clinical analysis validates these criteria to identify curable hypertension from unilateral renovascular or parenchymal disease. In patients with either occult or overt bilateral renal disease, the volume factor often predominates and is expressed by some suppression of plasma renin levels. Continued

Renin activation in the venous plasma from the involved kidney in the patient with renal hypertension

Measurements of plasma renin activity (PRA) in renal vein blood from the ischemic kidney are reported to be generally higher than from the contralateral kidney. Importance of factors other than renin content of renal venous plasma has not been investigated. Initial rate measurements of angiotensin generation with added excess of homologous renin (Plasma Renin Substrate Activity [PRSA]-20 min) were made in bilateral renal venous plasma from 31 patients suspected of suffering from unilateral renal hypertension. The mean values from the involved vs. the contralateral kidney were 551 vs. 331 ng respectively of angiotensin II equivalents generated per milliliter of plasma per 20 min of incubation. The measurement of maximal angiotensin generation under the same conditions with incubation prolonged to 3 hr (PRSA-180 min), however, were bilaterally equal in renal venous plasma from selected patients with renal hypertension who showed distinct differences in PRSA-20 min and PRA measurements. Prior extraction of plasma lipids did not significantly change the bilateral renal venous PRSA-20 min determinations. Stimulation of endogenous renin release in normal dogs did not change the PRSA determinations. The data suggest strongly the presence of a "renin activating" mechanism in the renal venous plasma from the involved kidney of patients with renal hypertension.