title: Microdialysis of noradrenaline in rostral ventrolateral medulla after intravenous methionine enkephalin administration in anesthetized rats.
abstract: The objective of this research was to define the role of central and peripheral opioid receptors for the regulation of cardiovascular action. Cardiovascular effects of methionine-enkephalin (met-enkephalin) after intracisternal, intravenous or direct administration into the rostral ventrolateral medulla (C1 area) were compared in inactin-anesthetized Sprague-Dawley rats. A microdialysis probe was stereotaxically implanted in the C1 area to dialyze monoamines during intravenous administration of met-enkephalin. An intravenous injection of met-enkephalin decreased both arterial pressure and heart rate in a dose-dependent manner. There were no cardiovascular responses to intracisternal dosages of up to 10 micrograms/kg, but as little as 0.1 micrograms/kg met-enkephalin decreased arterial pressure and heart rate after a direct injection into the C1 area. Onset of the met-enkephalin effect was similar regardless of drug doses after intravenous administration; however, duration and magnitude of the peptide's action and time to peak effect were directly related to the dose. Intravenous infusion of 100 micrograms/kg/min met-enkephalin increased the extracellular concentration of noradrenaline in the C1 area. There was a differential blockade by naloxone of the hypotensive action of met-enkephalin after intravenous or C1 administration. This study suggests the importance of both central and peripheral sites(s) of met-enkephalin for its cardiovascular action. Additionally, the data suggest that the C1 area is a communication site between catecholamines and opioid peptides for cardiovascular regulation.
authors.affiliation: Department of Pharmacology, Oral Roberts University School of Medicine, Tulsa, Oklahoma.
authors.forename: H M
authors.initials: HM
authors.lastname: Rhee
authors.forename: J A
authors.initials: JA
authors.lastname: Strickland
authors.forename: P A
authors.initials: PA
authors.lastname: Mason
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002946:Cisterna Magna; D004744:Enkephalin, Methionine / Q000008:administration & dosage / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects; D007262:Infusions, Intravenous; D007267:Injections; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects*; D009638:Norepinephrine / Q000032:analysis*; D051381:Rats; D011919:Rats, Inbred Strains; D013238:Stereotaxic Techniques
chemical_list: D004744:Enkephalin, Methionine; D009638:Norepinephrine