Evaluation of the antinociceptive action caused by ether fraction and a triterpene isolated from resin of Protium kleinii

This study investigates the antinociception caused by i.p. and p.o. administration of ether fraction and the triterpene identified as urs-12-ene-3 beta -16 beta -diol, known as Brein, isolated from Protium kleinii in several models of nociception in mice. The systemic administration of ether fraction (0.3 to 10 mg/kg, i.p. or 3 to 60 mg/kg, p.o.) caused a dose-related antinociception when assessed against acetic acid-induced writhing, with mean ID50 values of 1.2 and 16.4 mg/kg, respectively. The ether fraction (5 to 60 mg/kg, i.p. or 30 to 300 mg/kg, p.o.) also produced dose-related inhibition of both phases of formalin induced licking. The mean ID50, values for the early phase were > 60.0 and 62.1 mg/kg, while for the late phase they were 15.4 and 60.0 mg/kg, respectively, given by i.p. and p.o. routes. The ether fraction (3 to 30 mg/kg, i.p. or 10 to 100 mg/kg, p.o.) produced significant inhibition of the neurogenic nociception caused by topical injection of capsaicin, with mean ID50 values of 6.2 and 16.0 mg/kg, respectively. Given orally (I to 30 mg/kg) the ether fraction produced graded and pronounced inhibition of glutamate-induced hyperalgesia in mice with a mean ID50 value of 15.2 mg/kg. In contrast, the ether fraction failed to produce antinociception when assessed in the thermal model of pain, the tail flick and hot plate tests. The antinociception caused by the ether fraction, in contrast to that of morphine, was not reversed by naloxone when assessed in the formalin-induced licking. The ether fraction did not affect motor coordination or the core body temperature in mices The triterpene Brein isolated from P. kleinii, given by i.p. route (10 to 100 mg/kg) produced dose-related inhibition of both phases of formalin induced-licking, with mean ID50s Values of 15.3 and 20.6 for the early and the late phases, respectively. These data show that the active principle(s) present in the ether fraction from the resin of P. kleinii elicited pronounced antinociception when assessed by i.p. or p.o routes, against both inflammatory and neurogenic nociception. Such effects seem, at least in part, to be related to the presence of the triterpene Brein in the extract. The mechanisms responsible for the antinociceptive action are at this moment not completely understood, but the involvement of the opioid pathway seems unlikely. (C) 2001 Elsevier Science Inc. All rights reserved.