Antinociception caused by the extract of Hedyosmum brasiliense and its active principle, the sesquiterpene lactone 13-hydroxy-8,9-dehydroshizukanolide

The hydroalcoholic extract (HE) obtained from stems and leaves of Hedyosmum brasiliense, given i.p., produced significant inhibition of acetic acid-in duced abdominal constriction in mice, with a mean ID50 of 12.7 mg/kg. This effect installed rapidly (0.5 h) and lasted for up to 2 h. Given orally up to 1000 mg/kg, the HE was ineffective. When assessed in the formalin respon se the HE, given i.p., inhibited the first and second phase, with ID(50)s o f 31.1 and 21.7 mg/kg for the first and the second phases, respectively. Th e HE also inhibited capsaicin-induced neurogenic pain with ID50 of 69.0 mg/ kg, but, in contrast to morphine, failed to cause analgesia in either the t ail-flick or hot-plate models of pain. In addition, its antinociception was not reversed by naloxone. The sesquiterpene lactone 13-hydroxy-8,9-dehydro shizukanolide, isolated from H. brasiliense and already reported in other p lant species (given by i.p., i.t., or i.c.v. routes) exhibited graded antin ociception against acetic-acid writhing and capsaicin-induced licking. Addi tionally, we have corrected some physico-chemical data already reported for this compound. It is concluded that both the extract and the sesquiterpene lactone isolated from H. brasiliense produced marked antinociception in di fferent models of chemical pain. The site of action involved in the antinoc iception of the 13-hydroxy-8,9-dehydroshizukanolide remains unclear, but th e opioid pathway seems unlikely to be involved in its action.