Angiotensin II: dependence of hormone affinity on the electronegativity of a single side chain.

Structure-activity studies on rabbit aorta of angiotensin II analogues have suggested a possible relationship between the electronegativity of the aromatic side chain in position 4 (Tyr) and the observed affinity. In order to test this hypothesis, several other analogues modified in position 4 have been prepared, and all available analogues were tested in three bioassays: in vitro on rabbit aorta strip, in vivo on the rat blood pressure, and the binding assay on beef adrenocortical membranes. In all three bioassays the postulated correlation has confirmed that angiotensin II affinity depends inversely on the electronegativity of the aromatic side chain in position 4.