title: Selective alpha2-adrenergic properties of dexmedetomidine over clonidine in the human forearm.
abstract: We tested the hypothesis that dexmedetomidine (Dex) has greater alpha(2)- vs. alpha(1) selectivity than clonidine and causes more alpha(2)-selective vasoconstriction in the human forearm. After local beta-adrenergic blockade with propranolol, forearm blood flow (plethysmography) responses to brachial artery administration of Dex, clonidine, and phenylephrine (alpha(1)-agonist) were determined in healthy young adults before and after alpha(2)-blockade with yohimbine (n = 10) or alpha(1)-blockade with prazosin (n = 9). Yohimbine had no effect on phenylephrine-mediated vasoconstriction but blunted Dex-mediated vasoconstriction (mean +/- SE: -41 +/- 5 vs. -11 +/- 2%; before vs. after yohimbine) more than clonidine-mediated vasoconstriction (-39 +/- 5 vs. -28 +/- 4%; before vs. after yohimbine) (P < 0.02). Prazosin blunted phenylephrine-mediated vasoconstriction (-39 +/- 4 vs. -8 +/- 2%; before vs. after prazosin) but had similar effects on both Dex- (-30 +/- 4 vs. -39 +/- 6%; before vs. after prazosin) and clonidine-mediated vasoconstriction (-29 +/- 3 vs. -41 +/- 7%; before vs. after prazosin) (P > 0.7). Both Dex and clonidine reduced deep forearm venous norepinephrine concentrations to a similar extent (-59 +/- 12 vs. -55 +/- 10 pg/ml; Dex vs. clonidine, P > 0.6); this effect was abolished by yohimbine and blunted by prazosin. These results suggest that Dex causes more alpha(2)-selective vasoconstriction in the forearm than clonidine. The similar vasoconstrictor responses to both drugs after prazosin might be explained by the presynaptic effects on norepinephrine release.
authors.affiliation: Department of Anesthesiology, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.
authors.forename: Shizue
authors.initials: S
authors.lastname: Masuki
authors.forename: Frank A
authors.initials: FA
authors.lastname: Dinenno
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Joyner
authors.forename: John H
authors.initials: JH
authors.lastname: Eisenach
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage; D000328:Adult; D001783:Blood Flow Velocity / Q000187:drug effects / Q000502:physiology; D003000:Clonidine / Q000008:administration & dosage*; D020927:Dexmedetomidine / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D005260:Female; D005542:Forearm / Q000098:blood supply* / Q000502:physiology*; D006801:Humans; D007269:Injections, Intra-Arterial; D008297:Male; D014661:Vasoconstriction / Q000187:drug effects* / Q000502:physiology*; D014662:Vasoconstrictor Agents / Q000008:administration & dosage
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D014662:Vasoconstrictor Agents; D020927:Dexmedetomidine; D003000:Clonidine