Tetsu Maeda

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.

Specific 125I-Endothelin-1 Binding Sites in the Central Nervous System

The quantitative receptor autoradiographic method we used revealed that specific 125I-endothelin-1 (125I-ET-1) binding sites are highly concentrated in the choroid plexus (ChP), subfornical organ (SFO), lacunosum molecular layer of the hippocampus (LMol) and granular layer of the cerebellum (GC) of the rat brain. High densities of the binding sites were also observed in the laminae I-III and intermediolateral nucleus of the porcine spinal cord. 125I-ET-1 bound to the rat ChP and LMol with a high-affinity and to the SFO and GC with a low-affinity. The possibility that ET-1 acts as a neuropeptide within the central nervous system by interacting with specific receptors would have to be considered.

Specific [125I]brain natriuretic peptide-26 binding sites in rat and pig kidneys

Specific binding sites for porcine brain natriuretic peptide-26 (BNP-26), a member of the atrial natriuretic peptide family (ANPs), were investigated in the kidney by using receptor autoradiographic and membrane binding techniques with [125I]BNP-26. The binding sites were discretely localized in rat and porcine kidney areas corresponding anatomically to the glomeruli and inner medulla. There were no differences between the localization of [125I]BNP-26 and [125I]alpha-rat ANP binding sites in the kidney. [125I]BNP-26 binding to solubilized membranes from isolated glomeruli of the rat kidney was saturable, and a single class of high-affinity sites was labeled with a KD of 372 pM. The radioligand bound to two sites in solubilized inner medullary membranes of the rat, a low-affinity site with a KD of 30 nM, and a high-affinity site with a KD of 33 pM. The rank order of potency to inhibit binding was BNP-26 = alpha-rat ANP-(1-28) greater than atriopeptin III (ANP-(103-126)) much greater than atriopeptin I (ANP-(103-123)) greater than des-Cys105,Cys121- ANP-(104-126). Thus, [125I]BNP-26 presumably recognizes ANP receptors in the kidney. The possibility that BNP-26 regulates, as a circulating hormone, kidney functions by binding to ANP receptors would have to be considered.

Brain Natriuretic Peptide Binding Sites in Rat Kidney

Specific binding sites for [125I] porcine brain natriuretic peptide-26 ([125I]BNP-26) were investigated in the rat kidney by using receptor autoradiographic and membrane binding techniques. The binding sites were discretely localized in the glomeruli and inner medulla. There were no differences between the localization of [125I] BNP-26 and [125I] alpha-rat ANP binding sites. [125I]BNP-26 binding to solubilized membranes from isolated glomeruli of the rat kidney was saturable, and a single class of high-affinity sites. [125I]BNP-26 bound to two sites in solubilized inner medullary membranes. The rank order of potency to inhibit binding was BNP-26 = alpha-rat ANP (1-28) greater than atriopeptin III [ANP-(103-126)] much greater than atriopeptin I [ANP(103-123)] greater than des-Cys105, Cys121-ANP-(104-126). The possibility that BNP-26 regulates, as a circulating hormone, kidney functions by binding to ANP receptors would have to be considered.