Conversion of β-human atrial natriuretic polypeptide into α-human atrial natriuretic polypeptide in human plasma in vitro

Using synthetic β-human atrial natriuretic polypeptide (β-hANP), an antiparallel dimer of α-hANP, and radioimmunoassay (RIA) for α-ANP which also detects β-hANP, we investigated the disappearance profile and the change in the molecular form of exogenously added β-hANP in human plasma in vitro, compared with those of α-hANP. The ANP-like immunoreactivity (ANP-LI) level in β-hANP-added human plasma exhibited slower disappearance than that in α-hANP-added plasma during the incubation at 37°C. High performance-gel permeation chromatography and reverse phase-high performance liquid chromatography coupled with RIA revealed that β-hANP (6K) was converted into a smaller peptide with an approximate molecular weight of 3K corresponding to α-hANP during the incubation. Amino acid analysis and amino-terminal sequencing confirmed that the converted peptide from β-hANP in human plasma is authentic α-hANP. The demonstrated conversion of β-hANP into α-hANP in human plasma could be relevant to the in vivo natriuretic and diuretic actions with slower onset and longer duration of this unique peptide.