A modified quantitative autoradiographic assay for atrial natriuretic peptide receptors in rat brain

New conditions for quantitative autoradiographic determination of natriuretic peptide (ANP) binding in rat brain were developed in order to inhibit hormone degradation during incubation without the use of proteinase inhibitors. This procedure includes 1-h preincubation of tissue slices in hypotonic buffer and incubation at 4 degrees C in the presence of 4% proteinase-free albumin. ANP binding to choroid plexus and subfornical organ under above conditions reached equilibrium after 90 min. ANP degradation at the end of the incubation did not exceed 2%. Binding data analysis revealed the previously undetected presence of two distinct ANP binding sites in the rat choroid plexus.