PLASMA-PROTEIN INTERFERENCE IN ATRIAL-NATRIURETIC-PEPTIDE RIA - LARGEMOLECULAR-WEIGHT ATRIAL-NATRIURETIC-PEPTIDE IS A REAL CIRCULATING FORM

Although the main circulating form of human atrial natriuretic peptide is a 28 amino acid peptide (alpha-h ANP), large molecular weight form s 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 plas ma fractions after both C-18 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 interfe re in the direct RIA system either as cross-reacting or antibody-compe ting proteins. Moreover we searched for a non-specific binding of the tracer by plasma proteins other than IgG and HSA during the RIA. For t his purpose, we compared the bound radioactivity recovered by the dext ran-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 existe nce of ANP-binding components in normal human plasma, but the results as a whole confirm that large molecular weight ANP does exist in the b lood.