RESUMO
The present study was carried out to explore the antinociceptive as well as the anti-inflammatory effects of an ethanol extract of Stachytarpheta jamaicensis [L.] Vahl [EESJ] using 3 models of nociception and 2 models of inflammation in experimental animals EESJ was prepared by overnight soaking of the oven-dried [50°C; 72 h] ground leaves [500 g] in 80% ethanol [1:5; w/v]. The filtrate was evaporated to dryness [50°C], resuspended in distilled water at concentrations to provide the desired doses of 50, 100 and 150 mg/kg. For antinociceptive effects, 3 models were used: acetic acid-induced abdominal writhing, hot-plate- and formalin-induced paw-licking tests; for anti-inflammatory effects, 2 models were used - carrageenan-induced paw edema and cotton-pellet-induced granuloma tests. Appropriate doses were administered intraperitoneally [i.p.] to mice/rats prior to each test. The mechanisms of antinociceptive action of the extract were also investigated by pretreatment with naloxone [5 mg/kg, i.p.]. The extract exhibited significant [p < 0.05] antinociceptive activity in all nociceptive models tested with dose-dependent activity observed using the abdominal writhing and formalin tests. Pretreatment with naloxone partially, but significantly [p < 0.05] reversed the antinociceptive activity of the extract when assessed using the abdominal-writhing- and formalin-induced paw-licking tests, and completely inhibited its activity when the hot-plate test was used. The extract also showed significant [p < 0.05] anti-inflammatory activity in both the acute [carrageenan-induced paw edema test] and the chronic [cotton-pellet granuloma test] tests. This study showed the potential of EESJ to exert antinociceptive and anti-inflammatory activities, the former being modulated via peripheral and central mechanisms and involving, in part, activation of the opioid receptor system