Analgesic effect of agmatine and its enhancement on morphine analgesia in mice and rats

AIM: To study the effect of agmatine on pain and morphine analgesia. METHODS: The effect of agmatine on pain was observed in mouse heat radiant tail-flick test, mouse acetic acid writhing test, and rat 4 % saline test. Its enhancing effect on analgesia of morphine and clonidine was assessed in rat and mouse heat radiant tail-flick tests. RESULTS: Agmatine did not significantly prolong tail-flick latency of mice, but reduced the number of acetic acid-induced writhing of mice and inhibited writhing responses to saline completely. It potentiated the analgesic effects of morphine and clonidine in dose-dependent manner and decreased the analgesic ED50 Of morphine and clonidine by more than 75 % in mouse heat radiant tail-flick test. These effects of agmatine were antagonized by idazoxan. CONCLUSION: Agmatine has weak analgesic effects and potentiates morphine and clonidine analgesia by activativation of imidazoline receptors.