The effect of medetomidine, an alpha 2-adrenoceptor agonist, in various pain tests.
Medetomidine, a new alpha 2-adrenoceptor agonist produced dose-dependent (30-100 micrograms/kg i.p.) analgesia in the formalin test in rats, and this effect was reversed by atipamezole (1 mg/kg), a new alpha 2-adrenoceptor antagonist. However, medetomidine at the dose of 100 micrograms/kg did not influence tail flick latencies or latencies of the biting response to mechanical pinch stimuli. Moreover, medetomidine produced sedation and a decrease in locomotor activity. In comparison, the non-sedative monoaminergic agent, cocaine (25 mg/kg), produced highly significant analgesic effects in the formalin and mechanical pain tests. The cocaine effect in the formalin test was not reversed by atipamezole (1 mg/kg). It is concluded that the analgesic effect of medetomidine in the formalin test is due to supraspinal mechanisms related to sedation and is mediated by alpha 2-adrenoceptors. The alpha 2-adrenoceptors are not involved in cocaine-induced anagesia.
Pertovaara
A
A
Department of Physiology, University of Helsinki, Finland.
Kauppila
T
T
Tukeva
T
T
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000700:Analgesics; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003042:Cocaine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005557:Formaldehyde; D006993:Hypnotics and Sedatives; D007093:Imidazoles / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D008297:Male; D020926:Medetomidine; D009043:Motor Activity / Q000187:drug effects; D010147:Pain Measurement; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000187:drug effects
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000700:Analgesics; D006993:Hypnotics and Sedatives; D007093:Imidazoles; C050701:atipamezole; D005557:Formaldehyde; D003042:Cocaine; D020926:Medetomidine