Further antinociceptive properties of extracts and phenolic compounds from Plinia glomerata (Myrtaceae) leaves.

This study describes the antinociceptive activity of extracts (methanolic (ME) and acetonic (AE)) and two phenolic compounds, 3,4,3'-trimethoxyflavellagic acid (1) and 3,4,3'-trimethoxy flavellagic acid 4'-O-glucoside (2), from Plinia glomerata leaves, against different experimental models of pain in mice. When evaluated against writhing test, by i.p. route, ME and AE presented calculated ID(50) values (and respective confidence interval) of 3.28 (1.63-6.61) and 24.79 (16.57-37.09) mg/kg, respectively. Given by the oral route at 500 mg/kg, AE and ME extracts inhibited the abdominal constrictions by 60.5% and 35.3%, respectively. In the formalin test (10 mg/kg, i.p.), AE inhibited both phases of pain (45.6% in the first phase; 99.8% in the second phase) whereas ME inhibited 47.8% the first phase, and 92.6% the second phase. In the capsaicin test both extracts showed activity, with calculated ID(50) values of 6.56 (5.69-7.56) and 7.68 (4.94-11.93) mg/kg for AE and ME, respectively. When evaluated against the hot-plate test, both extracts demonstrated activity, but only in high doses. Compound 2, when evaluated against the formalin test (10 mg/kg, i.p.), inhibited both phases of pain (77.6%, first phase; 62%, second phase) whereas 1 inhibited only the first phase, with inhibition of 70%. When tested in the capsaicin and glutamate tests, at 10 mg/kg, i.p., 1 and 2 caused inhibitions of 41.5% and 37.9%, and 37.7% and 54.5%, respectively. These results confirm previous studies carried out by our research group regarding the antinociceptive properties of P. glomerata, stimulating other studies on mechanism of action as well as the determination of additional active principles in this plant.