A single beta-amino acid substitution to angiotensin II confers AT2 receptor selectivity and vascular function

Novel AT(2)R ligands were designed by substituting individual beta-amino acid in the sequence of the native ligand angiotensin II (Ang II). Relative ATR selectivity and functional vascular assays (in vitro AT(2)R-mediated vasorelaxation and in vivo vasodepressor action) were determined. In competition binding experiments using either AT(1)R- or AT(2)R- transfected HEK-293 cells, only beta-Asp(1)-Ang II and Ang II fully displaced [(125)I]-Ang II from AT(1)R. In contrast, beta-substitutions at each position of Ang II exhibited AT(2)R affinity, with beta-Tyr(4)-Ang II and beta-Ile(5)-Ang II exhibiting approximately 1000-fold AT(2)R selectivity. In mouse aortic rings, beta-Tyr(4)-Ang II and beta-Ile(5)-Ang II evoked vasorelaxation that was sensitive to blockade by the AT(2)R antagonist PD123319 and the nitric oxide synthase inhibitor L-NAME. When tested with a low level of AT(1)R blockade, beta-Ile(5)-Ang II (15 pmol/kg per minute IV for 4 hours) reduced blood pressure (BP) in conscious spontaneously hypertensive rats (beta-Ile(5)-Ang II plus candesartan, -24+/-4 mm Hg) to a greater extent than candesartan alone (-11+/-3 mm Hg, n=7, P