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Analgesic Properties of Umbellatine from Psychotria umbellata

Interesting analgesic activity has been previously identified in alkaloids isolated from the genus Psychotria (Rubiaceae). We here report the analgesic activity of umbellatine, a new glycoside indole monoterpene alkaloid isolated from Psychotria umbellata. Umbellatine produced a dose-dependent (100-300 mg/kg) analgesic effect, partially reversed by naloxone, in the tail-flick and hot-plate models. These results suggest an analgesic effect at least in part associated with the activation of opioid receptors. In the formalin- and capsaicininduced pain models, umbellatine (100-300 mg/kg) elicited significant and dose-related antinociception. Umbellatine acts synergistically when co-administered with the NMDA antagonist MK-801. These results indicate the involvement of NMDA receptors in the umbellatine mechanism of action. Such a combined mode of action can be of relevance for developing analgesics useful in neurophatic pain.