Atrial natriuretic peptide binding sites in the brain and pituitary gland of the toad, Bufo marinus: localisation and receptor characterisation

The distribution and nature of I-125-atrial natriuretic peptide binding sit es have been examined in the brain and pituitary gland of the toad, Bufo ma rinus, using tissue section autoradiography, affinity cross-linking and ele ctrophoresis, guanylyl cyclase assays and molecular analysis of natriuretic peptide receptor C (NPR-C) and NPR-GC mRNA expression. The highest density of I-125-atrial natriuretic peptide binding sites occurred in the dorsal p allium, the habenular region, the torus semicircularis, the choroid plexus, and the pituitary gland. Less dense binding was observed in the medial pal lium, the thalamic region, the hypothalamus, the optic tectum, and the inte rpeduncular nucleus. The natriuretic peptide receptor-C specific ligand, C- ANF displaced the binding in all brain regions; however, some residual bind ing was observed in the habenular region, the hypothalamus, the choroid ple xus, and the pituitary gland. In isolated brain membranes, 1 mu M rat atria l natriuretic peptide increased cyclic guanosine monophosphate levels to 90 % above basal. Affinity cross-linking followed by reducing electrophoresis showed that I-125-atrial natriuretic peptide bound to proteins of 65 kDa an d 135 kDa respectively. Furthermore, molecular analysis demonstrated that n atriuretic peptide receptor-C and guanylyl cyclase messenger ribonucleic ac id are expressed in the brain. In combination with the autoradiography, the data indicated that atrial natriuretic peptide acting via specific recepto rs could be important in natriuretic peptide regulation of the brain.