Low-renin essential hypertension (LREH) describes a widely recognized classification validated by clinical features, including salt-sensitive blood pressure and diuretic responsiveness. Classic physiological teaching has cited normal plasma aldosterone concentration despite suppressed renin as evidence for adrenal supersensitivity to angiotensin II (Ang II). We studied 94 patients with LREH, 242 normal-renin hypertensives, and 135 normal subjects as controls. Low-renin hypertensives did not differ significantly from the other groups in either basal or Ang II-stimulated aldosterone concentrations on a high-sodium diet. Stimulated with a low-sodium diet, LREH patients demonstrated the smallest rise in basal aldosterone secretion. Ang II responsiveness was also subnormal: the rise in aldosterone after Ang II infusion in LREH (613±39 pmol/L), although greater than in nonmodulators (180±17 pmol/L; P=0.001), was less than either the patients with intact modulation (940±53 pmol/L; P=0.001) or normotensives (804±50 pmol/L; P<0.05). Blacks with LREH demonstrated an even lower response than low-renin whites ((388±50 versus 610±47 pmol/L; P=0.0001). In contrast, the rise in systolic blood pressure with Ang II infusion on a low-salt diet was greatest among LREH patients (P=0.001). Patients with LREH and nonmodulators were equally salt-sensitive. These results indicate that the adrenal response in LREH is normal on a high-salt diet but becomes progressively more abnormal as sodium control mechanisms are stressed. The factors that mediate enhanced adrenal response to Ang II with sodium restriction may be defective, suggesting the existence of alternative physiological mechanisms for sodium homeostasis in the low-renin state.
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