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

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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.