Atrial natriuretic peptide (6-33) binding sites: decreased number and affinity in the subfornical organ of spontaneously hypertensive rats.

Binding sites for rat atrial natriuretic peptide (6-33) (rANP) were identified, localized and quantified in the subfornical organ and the choroid plexus of young and adult spontaneously (genetic) hypertensive rats (SHR) and normotensive, age-matched Wistar-Kyoto (WKY) controls. Our methods allowed the study of binding kinetics in discrete brain areas from single rats. We used newly developed autoradiographic techniques coupled to image analysis, microdensitometry and comparison with 125I-standards. Brain sections were first incubated with 125I-rANP to quantitate rANP sites. The number of rANP binding sites was much lower in both the subfornical organ and the choroid plexus of young and adult SHR when compared with normotensive controls. Analysis of binding kinetics in adult SHR showed lower maximum binding capacity (Bmax) in both the subfornical organ and the choroid plexus, and lower binding affinity (Ka) in the subfornical organ only, when compared to WKY. The results indicate a central role of rANP in the development and maintenance of spontaneous (genetic) hypertension in the rat.