Effects of analgesics on the plantar incision-induced drop of the noxious heat threshold measured with an increasing-temperature water bath in the rat.
The behavioural noxious heat threshold i.e. the lowest temperature evoking nocifensive behaviour was previously shown to decrease in short-lasting, but not in sustained, inflammatory thermal hyperalgesias. The aim of this study was to examine whether the surgical incision-induced lasting heat hyperalgesia involves a drop of the heat threshold and to assess the effects of conventional opioid and non-opioid analgesics in this model. One of the hind paws of rats was immersed into a water bath whose temperature was near-linearly increased from 30 degrees C until the animal withdrew its paw from the water. The corresponding bath temperature was considered as the behavioural noxious heat threshold. Hyperalgesia to heat was induced by a standardized plantar surgical incision performed under pentobarbital anaesthesia which led to a 5-7 degrees C decrease of the noxious heat threshold for seven days. Morphine, diclofenac, and paracetamol administered intraperitoneally 18 h after incision dose-dependently inhibited the drop of heat threshold with minimum effective doses of 0.3, 1, and 100 mg/kg, respectively, as assessed 20, 30 and 40 min after treatment. Thermal hyperalgesia was also decreased by intraplantar treatment with morphine (10 microg) or diclofenac (100 microg). In conclusion, the incision-induced sustained thermal hyperalgesia in rats involves a drop of the heat threshold suggesting that mechanisms of postsurgical pain are distinct from those of pure inflammatory pain. The thermal antihyperalgesic actions of systemically and/or locally applied morphine, diclofenac and paracetamol could be detected with high temporal resolution and sensitivity in this model.
Füredi
Réka
R
Department of Pharmacology and Pharmacotherapy, University of Pécs, Pécs, Hungary.
Bölcskei
Kata
K
Szolcsányi
János
J
Petho
Gábor
G
D000082:Acetaminophen / Q000008:administration & dosage / Q000494:pharmacology; D018712:Analgesics, Non-Narcotic / Q000008:administration & dosage / Q000494:pharmacology*; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D004008:Diclofenac / Q000008:administration & dosage / Q000494:pharmacology; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D005260:Female; D006358:Hot Temperature; D006930:Hyperalgesia / Q000188:drug therapy*; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology; D010146:Pain / Q000188:drug therapy; D017288:Pain Threshold / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D018712:Analgesics, Non-Narcotic; D000701:Analgesics, Opioid; D004008:Diclofenac; D000082:Acetaminophen; D009020:Morphine