Functional effects of activation of alpha-1 adrenoceptors by dexmedetomidine: in vivo and in vitro studies.
Dexmedetomidine, an alpha-2 adrenoceptor (AR) agonist, produces a biphasic hypnotic response in rats. Since central alpha-1 AR stimulation may reverse the hypnotic response produced by central alpha-2 AR stimulation, we have investigated, in both in vivo and in vitro models, the functional effects of dexmedetomidine on alpha-1 AR. For in vivo studies, stainless steel cannulas were inserted stereotaxically into the lateral ventricle of halothane-anesthetized rats to facilitate i.c.v. drug administration. Four to 7 days later, the alpha-1 AR antagonist prazosin (1 mg/kg-1) or saline was administered i.p. 15 min before i.c.v. injections of dexmedetomidine (10-333 micrograms) and the sleep-time (duration of loss of righting reflex) was assessed. The sleep-time increased, in a linear fashion, up to 33 micrograms; above this dose, there was a decrease in sleep-time. Pretreatment with prazosin prevented the decrease in sleep-time which was seen at higher doses. For in vitro studies, binding parameters of dexmedetomidine and its anesthetically inert L-isomer were determined from competition binding curves using [125I]2-[beta-(4-hydroxy-3-[125I]iodo- phenyl)ethylaminomethyl]-tetralone as the radiolabeled ligand and membranes prepared from HeLa cell lines stably expressing either alpha-1B or alpha-1C AR subtypes. Dexmedetomidine bound with equal affinity to both the alpha-1B (1178 +/- 63 nM) and the alpha-1C (1344 +/- 230 nM) isoreceptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Schwinn
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Department of Anesthesiology, Duke University Medical Center, Durham, North Carolina.
Correa-Sales
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D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D004247:DNA / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D006367:HeLa Cells; D006801:Humans; D007093:Imidazoles / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D020926:Medetomidine; D010716:Phosphatidylinositols / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D014162:Transfection
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D007093:Imidazoles; D010716:Phosphatidylinositols; D011942:Receptors, Adrenergic, alpha; D004247:DNA; D020926:Medetomidine