title: Nifedipine suppresses morphine-induced thermal hyperalgesia: evidence for the role of corticosterone.
abstract: It has been shown that systemic administration of morphine induced a hyperalgesic response at an extremely low dose. We have examined the effect of nifedipine, as a calcium channel blocker, on morphine-induced hyperalgesia in intact and adrenalectomized rats and on hypothalamic-pituitary-adrenal axis activity induced by ultra-low dose of morphine. To determine the effect of nifedipine on hyperalgesic effect of morphine, nifedipine (2 mg/kg i.p. and 10 microg i.t.) that had no nociceptive effect, was injected concomitant with morphine (1 microg/kg i.p. and 0.01 microg i.t. respectively). The tail-flick test was used to assess the nociceptive threshold, before and 30, 60, 120, 180, 240 and 300 min after drug administration. The data showed that low dose morphine systemic administration could produce hyperalgesic effect in adrenalectomized rats equivalent to sham-operated animals while intrathecal injection of morphine only elicited hyperalgesia in sham-operated animals. Nifedipine could block morphine-induced hyperalgesia in sham and adrenalectomized rats and even a mild analgesic effect was observed in the adrenalectomized group which was reversed by corticosterone replacement. Systemic administration of low dose morphine produced significant increase in plasma level of corticosterone. Nifedipine has an inhibitory effect on morphine-induced corticosterone secretion. Thus, the data indicate that dihydropyridine calcium channels are involved in ultra-low dose morphine-induced hyperalgesia and that both the pattern of morphine hyperalgesia and the blockage of it by nifedipine are modulated by manipulation of the hypothalamic pituitary adrenal axis.
authors.affiliation: Department of Physiology, Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Saeed
authors.initials: S
authors.lastname: Esmaeili-Mahani
authors.forename: Masoud
authors.initials: M
authors.lastname: Fereidoni
authors.forename: Mohammad
authors.initials: M
authors.lastname: Javan
authors.forename: Nader
authors.initials: N
authors.lastname: Maghsoudi
authors.forename: Fereshteh
authors.initials: F
authors.lastname: Motamedi
authors.forename: Abolhasan
authors.initials: A
authors.lastname: Ahmadiani
mesh_terms: D000315:Adrenalectomy; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000009:adverse effects*; D000818:Animals; D002121:Calcium Channel Blockers / Q000627:therapeutic use*; D003345:Corticosterone / Q000097:blood / Q000494:pharmacology / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D006358:Hot Temperature; D006930:Hyperalgesia / Q000188:drug therapy* / Q000209:etiology / Q000503:physiopathology; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects / Q000503:physiopathology; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000009:adverse effects*; D009543:Nifedipine / Q000627:therapeutic use*; D017288:Pain Threshold / Q000187:drug effects; D010913:Pituitary-Adrenal System / Q000187:drug effects / Q000503:physiopathology; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000701:Analgesics, Opioid; D002121:Calcium Channel Blockers; D009020:Morphine; D009543:Nifedipine; D003345:Corticosterone