Autoradiography of non‐AT‐1, non‐AT‐2 125‐I‐SI angiotensin II binding in neurolysin knock‐out and wild‐type mouse brains

Abstract

Recently a novel, non‐AT1, non‐AT2 binding site for angiotensin II (Ang II) was identified as the metalloendopeptidase neurolysin. To assess the localization of this binding site in brain, 3 mice deficient in neurolysin and 3 wild‐type mouse brains were evaluated for radioligand binding with 125I‐Sar1, Ile8 Ang II (250 pM) in the presence of AT1 and AT2 receptor‐saturating concentrations of losartan and PD123319, and 150 μM p‐chloromercuribenzoate using in vitro autoradiography. Specific (10 μM Ang II displaceable) 125I‐Sar1, Ile8 Ang II binding in wild‐type mouse brains was abundant, with highest levels in the molecular layer of the cerebellum, cerebral cortex, hippocampus, amygdala, caudate‐putamen, hypothalamus, lateral septum, and external plexiform layer of the olfactory bulb. Specific 125I‐Sar1, Ile8 Ang II binding in the neurolysin‐deficient mouse brains was profoundly reduced, however, the extent of reduction was region‐specific. Large decreases were seen in the cerebral cortex, substantia nigra, hippocampus, paraventricular thalamus, lateral septum, nucleus accumbens. Cerebellar cortex and hypothalamus showed moderate reduction in binding. These results confirm neurolysin as the novel non‐AT1, non‐AT2 receptor binding protein, but may reveal additional non‐AT1 non‐AT2 binding sites in the mouse brain. Supported by NHLBI HL‐096357