title: Experimental pain by ischaemic contractions compared with pain by intramuscular infusions of adenosine and hypertonic saline.
abstract: Deep tissue pain can be related to reduced muscle blood flow, which comprises the metabolic demand under muscle work. The tissues and receptors involved in nociception after ischaemic muscle contractions are not known. The concentration of adenosine is increased after ischaemic contractions and might act as an algesic substance. In 15 subjects, adenosine, hypertonic saline (algesic), and isotonic mannitol (placebo) were infused into the tibialis anterior muscle and compared with the pain caused by ischaemic contractions. The muscle pain intensity (visual analogue scale; VAS), distribution, and quality were assessed. Pressure pain thresholds were recorded to assess the deep tissue sensitivity. Adenosine did not induce more pain than the placebo. The maximal VAS score after hypertonic saline and ischaemic contractions was higher compared with adenosine/placebo infusions. The duration and area of pain were significantly increased after hypertonic saline infusions compared with ischaemic contractions. Higher scores on the McGill pain questionnaire were given to the "stabbing", "burning", "heavy", and "exhausting" word categories after ischaemic contractions, and "cramping" was rated higher during hypertonic saline-induced muscle pain compared with ischaemic contractions. During hypertonic saline infusions, the pressure pain threshold was decreased compared with before and immediately after the pain had vanished. The present study shows that pharmacological levels of adenosine in skeletal muscle did not induce pain. Excitation of muscle nociceptors by hypertonic saline evoked hyperalgesia, larger areas of pain, and a different quality of pain compared with ischaemic contractions, suggesting that the pain after ischaemic contractions is mediated by other populations of nociceptors in muscle and/or other tissues than excited by hypertonic saline.
authors.affiliation: Center for Sensory-Motor Interaction, Laboratory for Experimental Pain Research, Aalborg University, Fredrik Bajers Vej 7D-3, DK-9220 Aalborg E, Denmark. tgn@smi.auc.dk
authors.forename: Thomas
authors.initials: T
authors.lastname: Graven-Nielsen
authors.forename: Ylva
authors.initials: Y
authors.lastname: Jansson
authors.forename: Märta
authors.initials: M
authors.lastname: Segerdahl
authors.forename: Jens D
authors.initials: JD
authors.lastname: Kristensen
authors.forename: Siegfried
authors.initials: S
authors.lastname: Mense
authors.forename: Lars
authors.initials: L
authors.lastname: Arendt-Nielsen
authors.forename: Alf
authors.initials: A
authors.lastname: Sollevi
mesh_terms: D000241:Adenosine / Q000008:administration & dosage / Q000378:metabolism*; D000328:Adult; D015444:Exercise; D005260:Female; D006801:Humans; D007273:Injections, Intramuscular; D007511:Ischemia; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology / Q000503:physiopathology*; D009619:Nociceptors / Q000187:drug effects* / Q000378:metabolism*; D010146:Pain / Q000503:physiopathology*; D010147:Pain Measurement; D017288:Pain Threshold; D011312:Pressure; D012462:Saline Solution, Hypertonic / Q000008:administration & dosage / Q000009:adverse effects*; D014665:Vasodilator Agents / Q000008:administration & dosage / Q000378:metabolism*
chemical_list: D012462:Saline Solution, Hypertonic; D014665:Vasodilator Agents; D000241:Adenosine