Antinociceptive and anti-inflammatory effects of flavonoids PMT1 and PMT2 isolated from Piper montealegreanum Yuncker (Piperaceae) in mice.

In this study, we identified the antinociceptive and anti-inflammatory effects of two flavonoids (PMT1 and PMT2) from Piper montealegreanum. The antinociceptive effect was evaluated using the classical tests: acetic acid-induced writhing, formalin and hot plate test. PMT1 and PMT2 (0.1, 1, 30 and 100 μmol/kg, i.p.) reduced the writhings, with an ID50 of 0.58 and 0.44 μmol/kg, respectively. Moreover, these flavonoids (100 μmol/kg, i.p.) inhibited paw-licking time in the neurogenic phase of the formalin test, but only PMT2 was active in the inflammatory phase. However, PMT1 and PMT2 (100 μmol/kg, i.p.) did not increase the latency time of the animals in the hot plate. In order to evaluate the anti-inflammatory effect of these flavonoids, capsaicin-induced ear oedema was carried out. Both flavonoids (100 μmol/kg, i.p.) were active in this model. These results suggest that PMT1 and PMT2 have antinociceptive and anti-inflammatory activities.