Effects of halothane and isoflurane on beta-adrenoceptor-mediated responses in the vascular smooth muscle of rat aorta.

Abstract

Although previous studies have proposed that anesthetics may influence signal transduction systems, their effects on the beta-adrenoceptor-mediated system have not been fully characterized in vascular smooth muscle. The aim of this study was to determine how halothane and isoflurane affect beta-adrenoceptor-mediated vasodilation in rat aorta and what mechanisms were involved. Isometric tension and the intracellular calcium ion concentration ([Ca2+]i) were measured concomitantly in rat aortic strips from which the endothelium was removed. Strips precontracted with norepinephrine were dilated with the beta-adrenoceptor agonist, isoproterenol; the adenylyl cyclase activator, forskolin; or the membrane-permeable dibutyryl cyclic adenosine monophosphate (cAMP) with or without halothane or isoflurane. The effects of the anesthetics on each vasodilator were compared with the control responses. Beta-adrenoceptor binding characteristics and affinity for agonists were determined with [125I]-iodocyanopindolol with and without halothane or isoflurane. Furthermore, concentrations of cAMP induced by either isoproterenol or forskolin were measured with or without the anesthetics using an enzyme immunoassay procedure. Halothane and isoflurane attenuated vasodilation and [Ca2+]i decreases induced by isoproterenol, whereas both anesthetics only slightly affected vasodilation and [Ca2+]i decreases induced by forskolin and dibutyryl cAMP. Halothane and isoflurane had no effect on beta-adrenoceptor binding characteristics and affinity for agonists. Three percent halothane or 4% isoflurane significantly reduced cAMP levels induced by isoproterenol but not by forskolin. Halothane and isoflurane, at clinically relevant concentrations, can interfere with beta-adrenoceptor-mediated responses in the rat aorta at the steps after the agonist-receptor binding but before the adenylyl cyclase activation.