Injectable aspirin and mepyramine abolish post-ischaemic hyperalgesia in rats

We have investigated the effects of mepyramine, an H1 receptor antagonist, and lysine acetylsalicylate, a cyclo-oxygenase inhibitor, on post-ischaemic hyperalgesia in rats. We induced tail ischaemia in conscious rats by applying a tourniquet until the rats exhibited coordinated escape behaviour, when we released the tourniquet. We assessed hyperalgesia, by measuring tail flick latency following tail immersion in water at 49 degrees C, immediately after releasing the tourniquet and then at 30 min intervals for 2 h. After pretreatment with the drug vehicles, tail flick latency decreased significantly following ischaemia. Pretreatment with mepyramine maleate (3 mg/kg), or lysine acetylsalicylate (400 mg/kg), injected subcutaneously, abolished the decrease. We conclude that both histamine release and prostanoid synthesis are involved in the post-ischaemic hyperalgesia.