Regional Difference in the Response Mediated by β1-Adrenoceptor Subtype in Bovine Cerebral Arteries

Helical strips of bovine rostral cerebral arteries (anterior cerebral, middle cerebral, and internal carotid artery) responded to norepinephrine with contractions, whereas the caudal cerebral arteries (posterior communicating, posterior cerebral, and basilar artery) relaxed in response to the amine. After blockade of α-adrenoceptors, norepinephrine-induced rostral artery contractions were reversed to relaxations, which were smaller than those in the caudal arteries. Isoproterenol, dobutamine, and terbutaline produced greater relaxations in caudal than in rostral arteries, but forskolin relaxed these arteries to a similar magnitude. The isoproterenol-induced relaxation was not affected by removal of the endothelium. Maximal relaxations induced by terbutaline in caudal arteries were much inferior to those by isoproterenol, norepinephrine, and dobutamine. Relaxations caused by isoproterenol, norepinephrine, and terbutaline in the caudal arteries were attenuated by metoprolol, but not influenced by butoxamine. Relaxations mediated possibly by β 1 -adrenoceptor subtype are greater in bovine caudal cerebral arteries than in the rostral arteries. The heterogeneity does not appear to be associated with the different ability of cyclic AMP to relax arterial smooth muscle but with the difference of β-adrenoceptor populations and/or processes from the receptors to adenylate cyclase.