Development and Preliminary Application of a New Assay for Aldosterone Stimulating Factor

A new assay method has been developed to measure aldosterone stimulating factor (ASF) quantitatively. This method utilizes a combination of affinity chromatography and high pressure liquid chromatography (HPLC). Antibodies raised against ASF, coupled to Affi-Gel 10, were used as the affinity column, and adsorbed ASF was eluted with 4 M urea. Quantitation was based on the external standard method of analysis using the area of the standards as controls, which were previously tested by HPLC for purity. The amount of ASF in the unknown samples was calculated on the basis of the area of the peak emerging at the retention time of ASF. A parallel bioassay using adrenal glomerulosa cells was also done to assess the biological activity. In eight normal volunteers, the urinary ASF was 146 ± 4.6 ng/24 hr urine, whereas in plasma it was 70.5 ± 6.5 ng/100 ml. The method is reproducible, specific for ASF, and showed less than 3% inter- or intraassay variability. In a preliminary study, when ASF was quantified from the 24-hour urine of two patients with adrenal hyperplasia, a significantly higher level of ASF was found (750 and 1020 ng/24 hr urine). These data suggest that ASF may be of pathological significance in certain hypertensive patients, especially in the hypertension associated with hyperaldosteronism.