title: Experimental muscle pain and tenderness following infusion of endogenous substances in humans.
abstract: Several human models of myofascial pain exist, but none are similar to clinical pain. The aim of the present study was to develop a clinically relevant model of prolonged human myofascial pain using infusion of the naturally occurring endogenous substances. Initially, bradykinin (Bk), serotonin (5-hydroxytryptamine (5-HT)), histamine (His), prostaglandin E(2) (PGE(2)), adenosine-tri-phosphate (ATP), and their combinations were infused into the trapezius muscle of 36 healthy subjects in a total of 67 sessions to identify substances, which could induce a moderate muscle pain. PGE(2), ATP, and a combination of Bk, 5-HT, His, and PGE(2) produced the intended moderate pain. These substances were further examined in a randomised, blinded, placebo-controlled dose-finding design in 15 healthy subjects in 68 sessions. PGE(2) (3, 6, and 12 nmol/ml) induced mild pain and tenderness not different from placebo. ATP (9000, 18,000, and 36,000 nmol/ml) induced pain of moderate to strong intensity (P=0.04) and the dose of 18,000 nmol/ml furthermore produced moderate local tenderness (P=0.04). Because of unacceptable side effects in subsequent examinations, further studies of ATP in humans were suspended. Infusion of the combination of Bk (92 nmol), 5-HT (156 nmol), His (140 nmol), and PGE(2) (1.95 nmol) produced a moderate pain intensity (P=0.04) and mild tenderness (P=0.04) without inducing unacceptable side effects. Intramuscular infusion of a combination of Bk, 5-HT, His, and PGE(2) induced a prolonged moderate pain and tenderness in healthy humans, and this model may be a valuable tool in future studies of the pathophysiological mechanisms of myofascial pain.
authors.affiliation: Department of Neurology, Copenhagen Headache Center, Glostrup Hospital, University of Copenhagen, DK-2600 Glostrup, Copenhagen, Denmark. hjmoerk@dadlnet.dk
authors.forename: Hanne
authors.initials: H
authors.lastname: Mørk
authors.forename: Messoud
authors.initials: M
authors.lastname: Ashina
authors.forename: Lars
authors.initials: L
authors.lastname: Bendtsen
authors.forename: Jes
authors.initials: J
authors.lastname: Olesen
authors.forename: Rigmor
authors.initials: R
authors.lastname: Jensen
mesh_terms: D000328:Adult; D001685:Biological Factors / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004338:Drug Combinations; D005260:Female; D006801:Humans; D007273:Injections, Intramuscular; D008297:Male; D008875:Middle Aged; D009209:Myofascial Pain Syndromes / Q000139:chemically induced*
chemical_list: D001685:Biological Factors; D004338:Drug Combinations