ANGIOTENSIN RECEPTORS

Introduction The octapeptide angiotensin II, the potent effector molec ule of the renin-angiotensin system, has been implicated in the pathol ogy of hypertension, in cardiovascular diseases like cardiac left vent ricular hypertrophy and in structural alterations of the heart such as post-infarct remodelling. Angiotensin receptors The development of hi ghly selective angiotensin II receptor ligands allowed the identificat ion of angiotensin II receptor subtypes, designated AT(1), AT(2), AT(3 ) and AT(4). Most of the known effects of angiotensin II can be attrib uted to the AT(1) receptor (e.g. vasoconstriction, aldosterone and vas opressin release and proliferative effects on vascular smooth muscle a nd other cells). The AT(1) receptor is coupled to G-proteins and engag es classical intracellular second messenger systems, for example activ ation of phospholipase C or inhibition of adenylate cyclase. In contra st, the function and the signal transduction pathways of the AT(2) rec eptor, which exhibits only a 32-34% homology to the AT(1) receptor, ar e so far not fully understood. Coupling of the AT(2) receptor to phosp hatases and inhibitory actions on AT(1) receptor- and growth factor-me diated proliferation in endothelial and other cells as well as inducti on of neuronal outgrowth in PC12w cells have been demonstrated. Due to its wide distribution in fetal tissues including the central nervous system and its transient reappearance in the adult organism under path ological conditions (for instance after myocardial infarction) the AT( 2) receptor has been associated with cell differentiation and regenera tion. Receptor antagonists The application of orally active AT(1) rece ptor antagonists as antihypertensive drugs has, compared to angiotensi n converting enzyme inhibitors; the potential advantage of a more spec ific renin-angiotensin system inhibition. It is conceivable that the A T(2) receptor, left unopposed by AT(1) receptor antagonists, contribut es to some of the actions of these drugs.