Preparation of monoclonal antibodies against brain natriuretic peptide and their application to radioimmunoassay and passive immunization

Two monoclonal antibodies (mAbs) directed toward brain natriuretic peptide (BNP), KY-BNP-I and KY-BNP-II, have been produced. Both mAbs against BNP possessed high affinities for BNP, with association constants (K_a) of 4.0 × 10⁹ M^-1 (KY-BNP-I) and 2.0 × 10¹⁰ M^-1 (KY-BNP-II). With these mAbs, specific RIAs for BNP have been established. The least detectable quantities of BNP were 5 pg/tube (KY-BNP-I) and 1 pg/tube (KY-BNP-II). Cross-reactivities of α-human and rat atrial natriuretic polypeptides were less than 0.001%. These RIAs detected BNP-like immunoreactivity (BNP-LI) not only in the porcine brain but also in the canine brain, with the highest concentration in the medulla oblongata. These RIAs also detected BNP-LI in both the porcine and canine hearts and in the porcine plasma. The iv pretreatment of purified mAb[KY-BNP-II] almost completely blocked the hypotensive action of iv administered BNP in rats, with the concomitant suppression of BNP-induced increase of the plasma cyclic GMP level. These results indicate that our mAbs against BNP will serve as a useful tool for the elucidation of the physiological and pathophysiological significance of BNP as a neuropeptide and as a hormone.