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  • Title: Microdialysis of noradrenaline in rostral ventrolateral medulla after intravenous methionine enkephalin administration in anesthetized rats.
    Author: Rhee HM, Strickland JA, Mason PA.
    Journal: Can J Cardiol; 1992 Jun; 8(5):527-35. PubMed ID: 1617531.
    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.
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