The analgesic effect of agmatine on inflammatory pain and its influence on the analgesic effect of morphine / 中国药理学通报

ABSTRACT

Aim To evaluate the analgesic effect of agmatine on inflammatory pain and its influence on the analgesic effect of morphine. To investigate whether the mechanism of analgesic effect of agmatine is related to activation of imidazoline receptor or to affect the release of endogenous glutamate and gamma-aminobutyric acid (GABA) from rat spinal cord slices. Methods The formalin test in rats was used as a long-lasting inflammatory pain model. Effects of agmatine on basal and K+ evoked release of endogenous glutamate and GABA from rat spinal cord slices were determined by high performance liquid chromatography (HPLC). Results Pretreatment with agmatine (ip or sc) inhibited the second phase of the nociceptive response of rats and potentiated the analgesic effect of morphine in phase 2, but not in phase 1. Idazoxan did not attenuate the analgesic effect of agmatine. Agmatine (1, 10, 100, 1000 ?mol?L -1 ) had no effect on the basal release of glutamate and GABA from spinal cord slices, nor did it affect the K+ (50 mmol?L -1 ) evoked release of glutamate and GABA contents. Conclusions Agmatine has an analgesic effect and enhances morphine analgesia in the second but not the first phase of formalin-induced nociception. Its analgesic effect does not likely involve imidazoline receptor. The mechanism of the analgesic effect of agmatine may not be associated with inhibiting glutamate release nor increasing the GABA content.