Use of Positron Emission Tomography to Study AT1 Receptor Regulation In Vivo

Abstract

Abstract. Increased sodium intake and enhanced sodium sensitivity are implicated in the pathogenesis of hypertension and in the control of a major regulator of BP, the type 1 angiotensin receptor (AT1 receptor). An in vivo technique to study changes of renal AT1 receptors by dietary sodium was developed that uses positron emission tomography (PET). PET revealed that renal cortical AT1 receptor binding was increased in sodium-loaded compared with sodium-deprived dogs, which correlated with ex vivo estimations of AT1 receptor numbers. Plasma renin activity, angiotensin II, and aldosterone were inversely related to changes in AT1 receptor binding. These results demonstrate, for the first time in vivo, that the renal AT1 receptor is inversely related to the activity of the renin angiotensin system, which may provide a compensatory mechanism to prevent inappropriate fluctuations in arterial BP. The ability to measure AT1 receptor binding in vivo has potential significance for clinical studies of AT1 receptors, because PET is a noninvasive imaging technique that is readily applicable in humans.