[Heterogeneity of adrenoceptors in rat basilar and renal arteries]

A comparative study was made on the distribution of alpha- and beta-adrenoceptors between rat basilar (BA) and renal arteries (RA). The results showed that (1) the endothelium-independent relaxation due to beta-agonism was more significant in BA than that in RA; (2) there was no alpha 1-adrenoceptor-mediated vasoconstriction in most of the BA, only a small part of BA showed constriction in response to alpha 1-agonism, but with low affinity and efficacy and a desensitization tendency; (3) no response to alpha 2-agonist BHT 920 (10(-3) mol/L) in BA was shown, either in the presence or absence of endothelium. But in RA there was relaxation in the presence of endothelium and constriction in its absence. The above results suggest that there is a scarce distribution of alpha 1- and alpha 2-adrenoceptors, but an abundant distribution of beta-adrenoceptor in basilar artery compared with that in renal artery. The alpha 1-subtype in BA is different from the alpha 1-subtype in RA, and the alpha 2-receptor which mediates direct smooth muscle constriction and endothelium-dependent relaxation is highly heterogeneous between basilar and renal arteries.