Defining Angiotensin Receptor Subtypes

Angiotensin II, a primary effector hormone of the renin-angiotensin system, exerts a wide range of biological and biochemical effects in tissues associated with the cardiovascular, renal, endocrine, and neuronal functions. Two peptide AT₂-selective ligands, CGP42112A and pNH₂Phe-AngII, have been reported. They are characterized as AT₂-selective primarily by their distinctive receptor-binding profile. The original claim that CGP42112A was an antagonist was based on it ability to block AngII-induced contraction at micromolar concentrations. In terms of the molecular size, AT₂ appears to be slightly larger than the AT₁receptor. By covalent chemical crosslinking of AngII to its binding sites in tissue expressing exclusively AT₂receptors, a protein with apparent molecular weight of about 79 kDa was found in rat ovarian granulosa cell or one with about 100 kDa was noted in R3T3 cells. The apparent discrepancy between the two findings is not clear but the possibility of heterogeneity of AT₂ receptors may exist.