Antinociceptive properties of the methanolic extract and two triterpenes isolated from Epidendrum mosenii stems (Orchidaceae).

The antinociceptive effect of the methanolic extract (ME) and two triterpen es isolated from E. mosenii (Orchidaceae) has been investigated in chemical and thermal models of nociception in mice. The ME of E. mosenii (0.3-30 mg kg(-1), i.p. or 50-400 mg kg(-1), p.o.) produced dose-related, significant and long-lasting (4 to 6 h) inhibition of acetic acid-induced abdominal co nstriction, with ID50 values of 3.9 and 137.0 mg kg(-1) respectively. Pholi dotin and 24-methylenecycloartenol isolated from E. mosenii (0.1-3.0 mg kg( -1) i.p.) also produced marked and dose-related inhibition of acetic acid-i nduced pain, with ID50 values of 0.9 and 1.1 mg kg(-1) However, these compo unds and the ME were about 3- to 13-fold more potent at the level of ID50 t han diclofenac when assessed in acetic acid-induced abdominal constriction. The ME of E. mosenii in the same range of doses produced dose-related inhi bition of both phases of formalin-induced licking, with mean ID50 values fo r the first and the second phases of 0.9, 122.0 mg kg(-1) and 0.7, 258.0 mg kg(-1), respectively by i.p. or p.o. routes. In addition, the ME (0.3-30 m g kg(-1), i.p., or 50-400 mg kg(-1), p.o.) also caused dose-related inhibit ion of capsaicin-induced neurogenic pain with mean ID50 values of 5.2 and 1 30.0 mg kg, respectively. Treatment of animals with naloxone (5 mg kg(-1), i.p.) completely reversed the antinociceptive effect caused by morphine (5 mg kg(-1), s.c.) and that caused by ME off, mosenii (1 mg kg(-1), i.p.) whe n assessed against either phase of the formalin-induced pain. Furthermore, when assessed in the hot-plate test, ME: (100 mg kg(-1) i.p.) and morphine (10 mg kg(-1), s.c.) caused significant increase in response latency. Howev er, ME given daily for to 7 consecutive days did not-develop tolerance to i tself nor did it induce cross-tolerance to morphine. Taken together these d ata demonstrate that the ME of E. mosenii elicited pronounced antinocicepti on, when assessed by i.p. or p.o. routes, against several models of pain. I ts actions involve, at least in part, an interaction with opioid system, se eming. no to be related with a non-specific peripheral or central depressan t actions. Finally, the active principle(s) responsible for the antinocicep tive action of E. mosenii is likely related to the presence of the triterpe nes.