Abstract
Measurements of plasma renin activity (PRA) and aldosterone secretion are indispensable for preoperative diagnosis of primary aldosteronism.
Introduction of PRA assay by means of radioimmunoassay has made the PRA assay clinically available at present. However, the measurement of aldosterone secretion is still only for the investigational use account of complexities of the assay procedures.
Herein reported are our experiences on 13 cases of primary aldosteronism, in which diagnosis was based on measurements of PRA and plasma aldosterone concentration (PAC) by radioimmunoassay.
PRA is defined as angiotensin I generation by 1ml of plasma incubated at 37° for a unit hour under the condition in which plasma angiotensinases and converting enzyme are properly inhibited. The resultant angiotensin I is measured by radioimmunoassay using. a specific antibody against angiotensin I. PAC is measured by radioimmunoassay after aldosterone is extracted from the plasma with dichloromethane and partially purified by paper chromatography in Bush B5 system.
PRA was suppressed even after 3 days of salt restriction, followed by 80mg Furosemide per os administration, while PAC was always elevated on ad lib salt intake in all the 13 cases of primary aldosteronism. In 4 cases, PAC was measured on venous plasma obtained during adrenal venography. The concentration of aldosterone was approximately 10 to 20 times higher on the ipsilateral side of adenoma.
PAC is conceivably modified by the secretory rate of aldosterone as well as metabolic clearance thereof. Nevertheless, we believe the measurement of PAC by radioimmunoassay together with PRA is useful in clinical diagnosis of primary aldosteronism, provided PAC is clearly elevated on ad lib salt intake and that PRA is suppressed on salt restriction. The measurement of PAC is also useful in deciding the laterality of the adenoma.
