A new radioimmunoassay for human alpha atrial natriuretic peptide and its physiological validation

A new sensitive, specific radioimmunoassay for human alpha atrial natriuretic peptide (hANP) and a novel extraction method for hANP have been developed. Antiserum to hANP (Keq = 1.923 x 10(11) l/mol) showed no cross-reactivity with related analogues. Displacement of 50% bound 125I-hANP occurred at 4.7 +/- 0.1 fmol/tube (n = 15). The limit of detection of plasma hANP after extraction of 2 ml plasma with Florisil was 1.2 pmol hANP/litre plasma. The recovery of synthetic hANP from plasma over the range 6.5-162.5 pmol/l was 71.2 +/- 1.9%. Inter- and intra-assay coefficients of variation were 13.1% and 10.1% respectively. Extracted plasma was stored at -80 degrees C without loss in immunoreactivity. The radioimmunoassay was physiologically validated in man by measuring plasma hANP following central volume expansion - (a) plasma hANP rose from 2.5 +/- 0.5 to 4.1 +/- 0.6 pmol/l in 9 normal volunteers after postural change from seated to lying (b) infusion of normal saline (2 litre/2 hour) increased hANP from 1.6 to 4.3 pmol/l (n = 2). Infusion of hANP (2 pmol/kg/min) increased plasma hANP to 19.9 +/- 3.4 pmol/l (n = 6).