Radioimmunological determination of arginine vasopressin and human atrial natriuretic peptide after simultaneous extraction from plasma.

Human atrial natriuretic peptide and arginine vasopressin were coextracted from EDTA-plasma with Sep-Pak C18 cartridges, and the hormones were coeluted from the cartridges by a solution containing 900 ml/l of methanol, 5 ml/l of trifluoroacetic acid and 95 ml/l of water. After volume reduction under nitrogen the eluates were lyophilized, dissolved in buffer and aliquots were used for radioimmunological determination of both hormones. Both procedures used delayed addition of [125I]-labelled tracer to enhance sensitivity. Recoveries were 95 +/- 2% for human atrial natriuretic peptide and 96 +/- 3% vor arginine vasopressin (mean +/- SD). Minimal detectable doses were 2 pg/tube of human atrial natriuretic peptide and 0.5 pg/tube of arginine vasopressin (Bo - 3 SD). Intra-assay variabilities were +/- 8% for both tests. Simultaneous extraction of both hormones with high recovery was achieved, thus increasing sensitivity and specificity, at the same time reducing sample volume requirements and technician time.