Radioimmunoassay of atrial natriuretic peptides in human plasma

The concentration of atrial natriuretic peptide (hANP) in plasma from venous blood of healthy subjects was measured by radioimmunoassay. hANP from 5 mL of EDTA-treated plasma was adsorbed onto Sep-Pak C18 cartridges, which were eluted with methanol/trifluoroacetic acid (5 mL/L), 90/10 by volume. The eluates were concentrated by evaporation under nitrogen and lyophilized. After redissolving the samples in 0.5 mL of sodium phosphate buffer, we incubated 100-microL aliquots with anti-alpha-hANP for 24 h, then added 125I-labeled alpha-hANP tracer; 24 h later, we separated the bound and free fraction by adding an antibody/polyethylene glycol complex as the second antibody. The sensitivity of the assay was 2 pg per tube (B0-3 SEM). In the useful range of B = 15 to 85% of B0, CVs for within-run and between-run precision did not exceed 8 and 12%, respectively. The 50% intercept of the standard curve was at 12 pg per tube. hANP concentrations for 36 healthy adults ranged from 8 to 68 ng/L.