Antinociceptive and Anti-Inflammatory Effects of Stachytarpheta jamaicensis (L.) Vahl (Verbenaceae) in Experimental Animal Models

Objective: 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. Materials and Methods: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.). Results: The extract exhibited significant (p 0.05) antinociceptive activity in all nociceptive models tested with dose-depen-dent 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-writhingand 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.Conclusion: 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.