Receptor autoradiographic evidence of specific brain natriuretic peptide binding sites in the porcine subfornical organ.

Specific binding sites of brain natriuretic peptide (BNP), a newly discovered peptide in the subfornical organ (SFO) of porcine brain were investigated, following incubation of related tissue sections with 125I-BNP, then using autoradiography and an image analysis coupled with computer-assisted microdensitometry. Specific 125I-BNP binding sites were found to be localized in the SFO, an area densely labeled by 125I-alpha-rat atrial natriuretic peptide and 125I-(Sar1,Ile8)-angiotensin II. Specific 125I-BNP binding to the SFO was displaced by unlabeled BNP, with a high affinity, and was calculated to be Ka = 0.385 x 10(-9) M and Bmax = 40.1 fmol/mg using a LIGAND computer program. Acquisition of these present findings enhances our knowledge of the physiology of BNP, atrial natriuretic peptides and angiotensin II system in the SFO.