title: Regulation of alpha 1-, beta 1-, and beta 2-adrenergic receptors in rat heart by norepinephrine.
abstract: Previous studies suggest that the desensitization and downregulation of beta 1-adrenergic receptors (beta 1-AR) in the failing heart are the result of the elevated plasma catecholamine levels associated with this disease. To examine norepinephrine (NE)-induced regulation of cardiac adrenergic receptors, rats were infused with l-NE (200 micrograms.kg-1.h-1 for 7 days) or vehicle (0.001 N HCl) by implantation of osmotic minipumps. The technique of coverslip autoradiography was used to quantify alpha 1-adrenergic receptors (alpha 1-AR), beta 1-AR, and beta 2-AR in different tissue compartments of rat hearts. For measurement of beta-AR binding, sections were incubated with 70 pM [125I]iodocyanopindolol (ICYP) alone or in the presence of 5 microM dl-propranolol or 5 x 10(-7) M CGP-20712A (a beta 1-antagonist) and then set up for autoradiography. [3H]prazosin (1 nM) with or without phentolamine was used to study alpha-AR binding. Chronic infusion of NE induced a greater downregulation of beta 2-AR compared with beta 1-AR in all regions studied, including atrial and ventricular myocytes, coronary arterioles, and connective tissue. An 18% loss of beta 1-AR was seen only in atrial myocytes; beta 1-AR density actually increased 28% in ventricular myocytes following NE infusion. There was a 15% decrease in alpha 1-AR in ventricular myocytes, whereas no change in alpha 1-AR density was seen in myocardial arterioles. Our study demonstrates that beta 2-AR are more susceptible to NE-induced downregulation than beta 1-AR. Thus other mechanisms may be involved in the selective downregulation of beta 1-AR in certain forms of heart failure.
authors.affiliation: Department of Cell Biology and Neuroscience, University of Texas Southwestern Medical Center at Dallas 75235-9039, USA.
authors.forename: M
authors.initials: M
authors.lastname: Zhao
authors.forename: H K
authors.initials: HK
authors.lastname: Hagler
authors.forename: K H
authors.initials: KH
authors.lastname: Muntz
mesh_terms: D000818:Animals; D001345:Autoradiography; D006352:Heart Ventricles; D008297:Male; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D009336:Necrosis; D009638:Norepinephrine / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000378:metabolism; D011943:Receptors, Adrenergic, beta / Q000187:drug effects* / Q000378:metabolism
chemical_list: D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D009638:Norepinephrine