Antinociceptive effect of the hydroalcoholic extract of Bauhinia splendens stems in mice.

The analgesic effect of the hydroalcoholic extract of the stems of Bauhinia splendens (Leguminosae) has been investigated in chemical and thermal models of nociception in mice. The hydroalcoholic extract of B. splendens, 3-60 mg kg-1 intraperitoneally or 50-400 mg kg-1 orally, caused dose-related, and long-lasting (up to 3 h) inhibition of acetic acid-induced abdominal constriction in mice, with ID50 values of 3.2 and 177.6 mg kg-1 and maximum inhibition of 95 +/- 2 and 61 +/- 6%, respectively. In the formalin test, the extract given intraperitoneally (1-60 mg kg-1) or orally (50-400 mg kg-1) caused graded inhibition of both phases of formalin-induced pain, being about 5- to 6-fold more potent in attenuating the second phase of pain. The calculated mean ID50 values for the first and the second phases were 11.5 and 2.5 mg kg-1, respectively, for intraperitoneal administration and > 200 and 70 mg kg-1, respectively, for oral administration; the percentages of maximum inhibition for the first and the second phases were 68 +/- 6 and 99 +/- 1, respectively, for intraperitoneal administration and 37 +/- 6 and 69 +/- 9, respectively, for oral administration. However, at the same doses the extract did not significantly affect the oedematogenic response induced by formalin. The treatment of animals with naloxone (5 mg kg-1, i.p.) completely reversed the analgesic effect caused by morphine (5 mg kg-1, s.c.), but had no effect against the antinociceptive effect of the hydroalcoholic extract of B. splendens (60 mg kg-1, i.p.) when assessed against acetic acid-induced abdominal constrictions. Furthermore, the extract, in contrast with morphine, had no analgesic effect in the hot-plate test. These data show that the hydroalcoholic extract of B. splendens has significant analgesic action when assessed against several models of pain. The mechanism underlying its analgesic effect still remains unknown, but seems to be unrelated to interaction with opioid systems.