Plasma levels of alpha-atrial natriuretic peptide in normal subjects under various postural conditions.

The present paper describes a radioimmunoassay, in conjunction with an extraction procedure on octadecasilyl silica cartridges, of alpha-atrial natriuretic peptide in human plasma and its application in normal subjects under various postural conditions. The sensitivity of this assay is 1.96 pg/ml. The plasma concentrations of alpha-atrial natriuretic peptide in 18 normal male subjects ranged from 10 to 55 pg/ml. This assay was shown to be reproducible as indicated by the low within- and between-assay coefficients of variation. The plasma alpha-ANP concentration decreased during prolonged storage of the plasma at -20 degrees C or -80 degrees C and its level is also lower in hemolyzed plasma samples. The plasma alpha-ANP concentration is similar in standing and supine position but rose significantly when the subjects were tilted 20 degrees head-down.