Combination of high-performance liquid chromatography and radioimmunoassay for the measurement of urodilatin and α-hANP in the urine of healthy males

Urodilatin (ANP-(95–126)), a natriuretic peptide in urine, and α-hANP (ANP-(99–126)) are crossreactive in the radioimmunoassay of α-hANP (ANP-RIA). We therefore developed a method to separate physiological amounts of urodilatin and α-hANP in urine by high-performance liquid chromatography (HPLC) followed by ANP-RIA of the separated fractions. We studied urine samples of 10 healthy adult males with a plasma α-hANP level of 41±21 pg/ml (mean ± SD) and a total urinary ANP-RIA reactivity of 40±21 pg/ml. In all urine samples we found three peaks of ANP-RIA reactivity, the first one coeluting with synthetic urodilatin, the second one with the retention time of α-hANP and a late eluting ANP-RIA- reactive peak, possibly containing degradation products. The ratio of urodilatin/α-hANP was 0.77±0.17.