D. Measurements

Details of laboratory measurements and study procedures have been published elsewhere [17, 18]. In brief, all blood samples for this study were obtained after an overnight fast in the morning (8:00 to 11:00 am) after the patients had been seated for 10 minutes. Participants were advised to avoid smoking and taking their antihypertensive drugs in the morning before the blood collection.

Active renin concentration was measured in EDTA plasma by a Renin III Generation radioimmunoassay (Renin IRMA RIA-4541; DRG Instruments GmbH, Marburg, Germany), which has been calibrated against a World Health Organization standard [24]. Intra-assay and interassay coefficients of variation of this assay are 0.6% to 4.5% and 2.7% to 14.5%, respectively. PAC was measured by radioimmunoassay (Active Aldosterone RIA DSL-8600; Diagnostic Systems Laboratories, Inc., Webster, TX; now distributed by Beckman Coulter, Inc, Brea, CA.) with intra-assay and interassay coefficients of variation of 3.3%. to 4.5% and 5.9% to 9.8%, respectively [21].