Abstract

Sorghum bicolor (Family: Gramineae; Poaceae) is used traditionally for some ailments related to pain and inflammation. This study was therefore aimed at investigating possible antinociceptive and anti-inflammatory effects of this plant. The aqueous methanolic (70% methanol ) extract of the leaf base, its aqueous and ethylacetate fractions were evaluated for antinociceptive activity using acetic acid-induced writhing test (test on chemical pain) and tail flick test (test on mechanical pain) in Swiss albino mice. The site for antinociception was determined using formalin test in Wistar rats. Anti-inflammatory activity was evaluated using egg albumin-induced hind paw oedema in Wistar rats. Acute toxicity studies of all the extracts were also carried out on rats and mice to determine their LD₅₀. The aqueous methanolic extract and its aqueous fraction exhibited a significant (P < 0.05) antinociceptive activity while the ethylacetate fraction did not show antinociceptive effect. The aqueous methanolic extract showed higher percent pain inhibition in the early phase of formalin test but did not inhibit inflammation. The calculated oral LD ₅₀ value for the aqueous methanolic extract was ≥ 2000 mg/kg in both mice and rats. In rats, the calculated intraperitoneal LD ₅₀ value 48 h post treatment observation was 1,414.2 mg/kg while in mice, the calculated intraperitoneal LD ₅₀ value was 1341.6 mg/kg for 48 h post treatment time. The intraperitoneal LD₅₀ value for both aqueous and ethylacetate fractions were ≥ 2000 mg/kg 48 h post treatment. The study revealed that S. bicolor leaf base contains analgesic components which are probably more in the aqueous fraction of the crude extract. This effect appeared centrally mediated. The extract did not show anti-inflammatory property.

Key words: Sorghum bicolor, fractions, antinociception, anti-inflammation, acute toxicity.