title: Effects of reduced sympathetic activity on myocardial metaiodobenzylguanidine (MIBG) washout.
abstract: 1. Increase in myocardial sympathetic activity contributes markedly to the pathophysiology of conditions such as congestive heart failure and is also associated with myocardial infarction. However, measurement of myocardial sympathetic activity in vivo is difficult. 2. The present study assesses the effectiveness of metaiodobenzylguanidine (MIBG) imaging to characterize modulation of sympathetic activity, as induced by dexmedetomidine, a highly specific alpha-2 adrenoceptor agonist. 3. We imaged washout of [125I]-MIBG from rabbit heart before and during two consecutive 45-min intravenous infusions of dexmedetomidine (10 microg kg(-1) followed by 16 microg kg(-1)) (n=9) or of saline (n=9). 4. Heart rate (HR), and mean blood pressure (BP) were measured before and at the end of each study period. Plasma noradrenaline (NA) was measured before and after study drug infusion. The hearts were then excised and biopsied for MIBG tissue concentration [MIBG] (% kg-dose g(-1)). 5. Relative to saline controls, dexmedetomidine significantly decreased HR, BP, plasma NA and MIBG washout. There was an inverse correlation between MIBG washout and residual [MIBG] in the myocardium (r= -0.75, P < 0.01). 6. These data suggest that a reduction of sympathetic nervous system activity causes a decrease in myocardial MIBG washout in vivo in rabbits, and confirms the usefulness of MIBG scintigraphy as a non-invasive tool to measure changes in myocardial sympathetic activity.
authors.affiliation: Department of Radiology, University of California, San Francisco, CA, USA.
authors.forename: D W
authors.initials: DW
authors.lastname: Gao
authors.forename: P O
authors.initials: PO
authors.lastname: Talke
authors.forename: M W
authors.initials: MW
authors.lastname: Dae
mesh_terms: D019797:3-Iodobenzylguanidine / Q000493:pharmacokinetics*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics*; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009638:Norepinephrine / Q000097:blood; D011817:Rabbits; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*
chemical_list: D000316:Adrenergic alpha-Agonists; D004791:Enzyme Inhibitors; D019797:3-Iodobenzylguanidine; D009638:Norepinephrine