Agmatine, an endogenous ligand, interacts both with the α2-adrenoceptors and with the imidazoline binding sites. The effect of intrathecally administered agmatine on carrageenan-induced thermal hyperalgesia was investigated by means of a paw-withdrawal test in rats. The effect of agmatine on morphine-induced anti-hyperalgesia was also studied. Intrathecal agmatine in doses larger than 250 μg caused a decrease in the pain threshold, with vocalization and agitation lasting for several hours in all animals. Agmatine alone at 1-100 μg did not give rise to any change in the thermal withdrawal threshold in the contralateral non-inflamed paw. Agmatine pretreatment was found to dose-dependently attenuate the thermal hyperalgesia induced by intraplantar carrageenan. The effect of 100 μg agmatine was completely lost by 60 min, whereas the effect of 50 μg was of similar magnitude but exhibited a longer duration. Agmatine posttreatment had a slighter effect. Agmatine pretreatment (100 μg) together with 1 μg morphine (subeffective dose) has significantly higher anti-hyperalgesic effect then the individual compounds by themselves. These are the first data demonstrating the behavioral and anti-hyperalgesic effects of intrathecal agmatine. The results reveal important interactions between intrathecal agmatine and opioids in thermal hyperalgesia. Copyright (C) 1999 Elsevier Science B.V.
- Imidazoline binding site
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