Agmatine blocks morphine-evoked hyperthermia in rats.

The present study investigated the effect of agmatine on morphine-evoked hyperthermia in rats. Morphine (4 mg/kg, s.c.) produced hyperthermia by activating mu opioid receptors. Agmatine (10 and 50 mg/kg, i.p.) was ineffective. For combined administration, agmatine decreased morphine-evoked hyperthermia. The effect was prevented by idazoxan (5 mg/kg, i.p.), an imidazoline/alpha(2)-adrenoeceptor receptor antagonist. Yohimbine, an alpha(2)-adrenoeceptor antagonist, did not prevent the attenuation of morphine-evoked hyperthermia by agmatine. The present data provide pharmacological evidence that agmatine blocks the hyperthermic effect of morphine by activating imidazoline receptors.