title: Beta-adrenoceptor dysfunction after inhibition of NO synthesis.
abstract: G(s) protein-coupled beta-adrenoceptors rapidly desensitize on exposure to agonists in reconstituted membrane preparations, whereas rapid tachyphylaxis to beta-adrenoceptor-mediated vasodilation does not readily occur in vivo. This study examined the possibility that endothelium-derived nitrosyl factors prevent the rapid desensitization of beta-adrenoceptors in the vascular smooth muscle of resistance arteries in pentobarbital-anesthetized rats. The fall in mean arterial blood pressure and in hindquarter vascular resistance produced by the beta-adrenoceptor agonist isoproterenol (ISO, 0.1 to 10 microg/kg IV) was slightly but significantly smaller in rats treated with the NO synthase inhibitor N:(G)-nitro-L-arginine methyl ester (L-NAME, 100 micromol/kg IV) than in saline-treated rats. The ISO-induced fall in mesenteric resistance was similar in L-NAME-treated and in saline-treated rats. The fall in hindquarter vascular resistance and in mesenteric resistance produced by ISO (8 x 10 microg/kg IV) was subject to tachyphylaxis on repeated injection in rats treated with L-NAME (100 micromol/kg IV) but not in rats treated with saline. Injections of L-S:-nitrosocysteine (1200 nmol/kg IV), a lipophobic S:-nitrosothiol, before each injection of ISO (10 microg/kg IV) prevented tachyphylaxis to ISO in L-NAME-treated rats. The vasodilator effects of ISO (0.1 to 10 microg/kg IV) in L-NAME-treated rats that received 8 injections of ISO (10 microg/kg IV) were markedly smaller than in L-NAME-treated rats that received 8 injections of saline. These results indicate that (1) the vasodilator actions of ISO in pentobarbital-anesthetized rats only minimally involve the release of endothelium-derived nitrosyl factors, (2) the effects of ISO are subject to development of tachyphylaxis in L-NAME-treated rats, and (3) tachyphylaxis to ISO is prevented by L-S:-nitrosocysteine. These findings suggest that endothelium-derived nitrosyl factors may prevent desensitization of beta-adrenoceptors in vivo.
authors.affiliation: Department of Pharmacology, The Cardiovascular Center, University of Iowa, Iowa City 52242, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Whalen
authors.forename: A K
authors.initials: AK
authors.lastname: Johnson
authors.forename: S J
authors.initials: SJ
authors.lastname: Lewis
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D003545:Cysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006439:Hemodynamics / Q000187:drug effects* / Q000502:physiology; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D009603:Nitroso Compounds / Q000494:pharmacology; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000502:physiology*; D026403:S-Nitrosothiols; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology
chemical_list: D000318:Adrenergic beta-Agonists; D004791:Enzyme Inhibitors; D009603:Nitroso Compounds; D011943:Receptors, Adrenergic, beta; D026403:S-Nitrosothiols; D009569:Nitric Oxide; C021315:S-nitrosocysteine; D003545:Cysteine; D007545:Isoproterenol; D019331:NG-Nitroarginine Methyl Ester