Decreased number and affinity of rat atrial natriuretic peptide (6-33) binding sites in the subfornical organ of spontaneously hypertensive rats.

Binding sites for rat atrial natriuretic peptide (6-33) were quantified by incubation of brain sections with (3-[125I]iodotyrosyl28) rat atrial natriuretic peptide (6-33), followed by autoradiography with computerized microdensitometry. Spontaneously hypertensive rats present lower numbers and lower affinity of binding sites than normotensive controls, Wistar-Kyoto rats, in the subfornical organ (binding capacity 61.7 +/- 8.9 and 124.3 +/- 10.7 fmol/mg protein; affinity constant 4.25 +/- 0.55 and 11.10 +/- 1.67 X 10(9) M-1, respectively). In the choroid plexus, hypertensive rats have lower numbers of sites than normotensive rats (binding capacity 72.7 +/- 10.5 and 173.6 +/- 22.8 fmol/mg protein, respectively), but there was no difference in the binding affinity (affinity constant 6.28 +/- 0.82 and 7.60 +/- 2.06 X 10(9) M-1, respectively). Our results suggest that discretely localized brain binding sites for rat atrial natriuretic peptide (6-33) may have a physiological function in genetically hypertensive rats.