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

Increased sodium intake and enhanced sodium sensitivity are implicated in t he pathogenesis of hypertension and in the control of a major regulator of BP, the type 1 angiotensin receptor (AT(1) receptor). An in vivo technique to study changes of renal AT(1) receptors by dietary sodium was developed t hat uses positron emission tomography (PET). PET revealed that renal cortic al AT(1) receptor binding was increased in sodium-loaded compared with sodi um-deprived dogs, which correlated with ex vivo estimations of AT(1) recept or numbers. Plasma renin activity, angiotensin II, and aldosterone were inv ersely related to changes in AT(1) receptor binding. These results demonstr ate, for the first time in vivo, that the renal AT(1) 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 AT(1) receptor binding in vivo has potential si gnificance for clinical studies of AT(1) receptors, because PET is a noninv asive imaging technique that is readily applicable in humans.