Assessment of alpha-adrenergic receptor subtypes in isolated rat aortic segments

Abstract

The postsynaptic α-adrenoceptors in the isolated rat aorta have been characterized according to the sensitivity of the tissue to selective α₁- and α₂-adrenoceptor agonists and antagonists. The potency (-log EC₅₀) order of the non-selective α-agonist norepinephrine and relatively selective agonists was as follows: norepinephrine (α₁=α₂; 7.30); clonidine (α₂>α₁; 7.01); phenylephrine (α₁>α₂; 6.99), SK & F 89748-A (α₁>α₂; 6.65); BHT-920 (α₂≫α₁; 5.56) and M-7 (α₂>α₁; 4.66). The isolated rat oarta was 12–200-fold more sensitive to the α₁-adrenoceptor agonists phenylephrine and SK & F 89748-A, than to the α₂-agonists, BHT-920 and M-7. Prazosin is 245–1259-fold more potent than rauwolscine as an antagonist of contractions induced by various α₁- and α₂-agonists in the rat aorta. These data indicate that constriction of the smooth muscle of the rat aorta to α-adrenergic agonists is mediated through α₁- but not α₂-adrenoceptors.