Postjunctional ?-adrenoceptors

Abstract

The postsynaptic α-adrenoceptors in rat aorta and in pithed rat were investigated according to their sensitivity to nine α-adrenergic agonists and to the selective antagonists yohimbine (α₂) and prazosin (α₁) and the non-selective one, phentolamine. In addition, in radioligand binding studies, the affinity and selectivity of the drugs were determined on rat cerebral cortex using [³H] yohimbine and [³H] prazosin. On rat aorta, prazosin is 1,000 times more potent than yohimbine against each α-adrenoceptor agonist, whether α₁- or α₂-selective. Rat aorta probably contains only α₁-adrenoceptors. Pressor effects in pithed rats are mediated by post-junctional α₁- and α₂-adrenoceptors. The dose-response curve for α-methylnorepinephrine in the presence of prazosin, using Hofstee's plots, revealed α₁- and α₂-adrenoceptors, respective proportions being 80.5 and 19.5%