title: Intradermal injection of norepinephrine evokes pain in patients with sympathetically maintained pain.
abstract: Tissue injuries, with or without involvement of nerves, may lead to ongoing pain and hyperalgesia to external stimuli. In a subset of patients, the pain is maintained by sympathetic efferent activity (SMP). We investigated if the peripheral administration of the alpha-adrenergic agonist, norepinephrine (NE), in physiologically relevant doses resulted in pain in patients with SMP. To establish the dose of intradermal NE required to induce cutaneous vasoconstriction, NE (1 nM-10 microM, 30 microl) was injected under a laser Doppler probe on the volar forearm of seven normal subjects. A decrease in blood flow was evident at a dose of 10 microM. Twelve patients (five male, seven female) diagnosed to have SMP based on the decrease in pain by a local anesthetic sympathetic blockade (70+/-6%) were enrolled in the study. Pain ratings were obtained continuously for 5 min after intradermal injections of saline and NE (0.1-10 microM) into their hyperalgesic zone and the mirror-image contralateral side. Injections were done during the period of pain relief following a local anesthetic sympathetic blockade. Similar injections were made in eight control subjects. On the affected side of the patients, the two highest concentrations of NE (1 and 10 microM) caused significantly more pain than saline (P<0.05, ANOVA). In contrast, there was no significant pain induced by the NE injections in the unaffected side and in control subjects. Six of nine patients tested reported a marked decrease in pain and hyperalgesia following infusion of phentolamine (1 mg/kg over 10 min). Two of the three patients who did not receive pain relief following phentolamine infusion also did not report pain to the NE injections. We conclude that NE injections produce pain in SMP patients at doses that are at the threshold for producing vasoconstriction. These studies support a role for cutaneous adrenoceptors in the mechanisms of sympathetically maintained pain.
authors.affiliation: Department of Neurological Surgery, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, The Johns Hopkins Hospital, 600 N. Wolfe Street, Osler 292, Baltimore, MD 21287, USA Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21287, USA.
authors.forename: Zahid
authors.initials: Z
authors.lastname: Ali
authors.forename: Srinivasa N
authors.initials: SN
authors.lastname: Raja
authors.forename: Ursula
authors.initials: U
authors.lastname: Wesselmann
authors.forename: Perry N
authors.initials: PN
authors.lastname: Fuchs
authors.forename: Richard A
authors.initials: RA
authors.lastname: Meyer
authors.forename: James N
authors.initials: JN
authors.lastname: Campbell
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D000328:Adult; D020918:Complex Regional Pain Syndromes / Q000503:physiopathology*; D005260:Female; D005728:Ganglia, Sympathetic / Q000187:drug effects; D005730:Ganglionic Blockers / Q000494:pharmacology; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced / Q000473:pathology; D007262:Infusions, Intravenous; D007271:Injections, Intradermal; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000008:administration & dosage / Q000494:pharmacology*; D010146:Pain / Q000139:chemically induced* / Q000503:physiopathology; D010147:Pain Measurement / Q000187:drug effects; D010646:Phentolamine / Q000008:administration & dosage / Q000494:pharmacology; D011601:Psychophysics; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D005730:Ganglionic Blockers; D009638:Norepinephrine; D010646:Phentolamine