Plasma protein interference in atrial natriuretic peptide RIA: Large molecular weight atrial natriuretic peptide is a real circulating form
Maioli, E.; Camporeale, A.; Torricelli, C.; Campoccia, G.; Pacini, A.
Biochemical Archives 13(4): 297-305
ISSN/ISBN: 0749-5331 Accession: 009941333
Although the main circulating form of human atrial natriuretic peptide is a 28 amino acid peptide (alpha-h ANP), large molecular weight forms higher than 60 kDa (big ANP) have also been described. This material is generally considered to be a plasma protein interference in RIAs. Since high molecular weight immunoreactivity had been detected in plasma fractions after both C18 Sep-Pak and Affi-Gel Blue chromatography, we evaluated the ANP immunoreactivity of human immunoglobulin G (hIgG) and human serum albumin (HSA) subjected to the same chromatographic techniques. The results demonstrate that these proteins do not interfere in the direct RIA system either as cross-reacting or antibody-competing proteins. Moreover we searched for a non-specific binding of the tracer by plasma proteins other than IgG and HSA during the RIA. For this purpose, we compared the bound radioactivity recovered by the dextran-coated charcoal (DCC) method (specific plus non-specific binding) to that obtained by the double antibody (DA) method (specific binding). The present experimental approach does not throw light on the existence of ANP-binding components in normal human plasma, but the results as a whole confirm that large molecular weight ANP does exist in the blood.