Isolation of a dihydrobenzofuran lignan, icariside E4, with an antinociceptive effect from Tabebuia roseo-alba (Ridley) Sandwith (Bignoniaceae) bark.

The antinociceptive activity of icariside E4, a dihydrobenzofuran-type lignan isolated from Tabebuia roseo-alba (Ridley) Sandwith (Bignoniaceae) bark, was evaluated in mice by using chemical and thermal models of nociception. Intraperitoneal (i.p.) administration of crude T. roseo-alba bark extract and its methanol fraction inhibited acetic acid-induced abdominal constriction in mice. Furthermore, i.p. administration of 0.1, 1, and 10 mg/kg of icariside E4 reduced the number of writhes evoked by acetic acid injection by 46.9, 82.3, and 66.6%, respectively. Icariside E4 administration had no effect in the first phase of the formalin test, but it reduced nociceptive behavior in the second phase as indicated by a reduction in the licking time. Icariside E4 did not modify thermal nociception in the hot-plate test model, suggesting that it had a peripheral antinociceptive action. The antinociceptive effect of icariside E4 in the writhing test was reversed by pre-administration of glibenclamide, but not of naloxone, atropine, yohimbine, or haloperidol. Together, these results indicated that the antinociceptive activity of icariside E4 from T. roseo-alba in models of chemical pain occurred through ATP-sensitive K(+) channel-dependent mechanisms.