LocaIization of 125l‐labelled α‐r‐atriaI natriuretic peptide in rat tissues by whole‐body and microautoradiography

125 I‐labelled α rat atrial natriuretic peptide (28 amino acids: Ser 99‐Tyr 126) ( 125 I α‐rANP) was given i.v. to SpragueDawley rats and the distribution of radioactivity in the tissues was examined by whole‐body and microautoradiography at intervals from 2 min to 4 h after the administration. Inhibition of uptake of the 125 1α‐rANP by simultaneous injection of an excess of non‐labelled α‐rANP was taken as an indication that highly labelled structures in rats injected with 125 Iα(‐rANP alone are due to an abundance of specific receptors for the peptide. In the rats given only the 125 Iα‐rANP a rapid and high radioactivity occurred in the renal glomeruli, the endocardium of the heart ventricles, the endothelium of the processus ciliares of the eyes, the portal vessels and a few larger vessels of the liver, the subcapsular vessels of the adrenal glands and the parenchyma of the lungs. Other tissues showing a distinct, but less prominent, radioactivity were the endocardium of the heart atria, the walls of the great afferent and efferent vessels in the thoracic cavity, the choroid plexuses of the brain ventricles, the pia mater, brown fat, the muscularis layer of the stomach and the intestines, the lamina propria of the villi in the small intestine and the walls of a few small blood vessels in the kidney medulla. The specific labelling was highest at 2 min after injectian and then diminished at later intervals. Several of the labelled structures are localized in tissues involved in the regulation of blood pressure, and fluid and electrolyte homeostasis, processes in which the atrial peptides are considered to play a role. It is suggested that high concentrations of receptors are present at the sites at which the 125 Iα‐rANP was strongly localized and that biological effects of the atrial peptides are everted via these structres.