A monoclonal antibody against N-terminus of α-atrial natriuretic polypeptide (α-ANP): A useful tool for preferential detection of naturally circulating ANP

A monoclonal antibody directed against the N-terminus of α-atrial natriuretic polypeptide (α-ANP), named KY-ANP-II, was produced by fusion of a non-producing mouse myeloma cell line, X63-Ag8.653, with spleen cells from a BALB/c mouse immunized with synthetic α-human ANP (α-hANP) conjugated to bovine thyroglobulin. The obtained antibody showed a high affinity for α-hANP with a Ka of 6.6 x 10¹⁰ M^-1. With this monoclonal antibody, a specific radioimmunoassay for α-hANP was established. The minimal detectable level of α-hANP in this radioimmunoassay was 0.8 fmol (2.5 pg)/tube, and IC₅₀ was 8 fmol (25 pg)/tube. The radioimmunoassay recognized α-rat ANP on an equimolar basis, whereas there was no detectable cross-reactivity with α-ANP [4-28] or α-ANP [5-28]. Thus, the monoclonal antibody can detect a hormonal form of ANP, α-ANP, but not neuropeptide forms of ANP, α-ANP [4-28] and α-ANP [5-28]. These results indicate that KY-ANP-II becomes a useful tool for preferential detection of a circulating form of ANP and for investigation of the physiological and pathophysiological significance of ANP as a hormone.