Use of positron emission tomography to study AT1 receptor regulation in vivo

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.