The present study evaluated the antihyperglycaemic effect and mechanism of action of fractions of the aqueous seed extract of Hunteria umbellata (K. Schum.) Hallier f. (HU) in normal and alloxan-induced hyperglycaemic rats. HU was partitioned in chloroform, acetyl acetate and butan-1-ol to give chloroform fraction (HU c ), ethyl acetate fraction (HU e ), butanol fraction (HU b ) and the "residue" (HU m ), respectively. 200 mg/kg of each of these fraction dissolved in 5% Tween 20 in distilled water was investigated for its acute oral hypoglycaemic effects in normal rats over 6 hours while its repeated dose antihyperglycaemic effect was evaluated in alloxan-induced hyperglycaemic rats over 5 days. In addition, 50 mg/kg of the crude alkaloid fraction (HU Af ) extracted from HU was evaluated for its possible antihyperglycaemic activity in alloxaninduced hyperglycaemic rats using oral glucose tolerance test (OGTT) over 6 hours. Using the solvent system, distilled water-butanol-ammonium hydroxide (2:15:1, v/v/v), HU b was chromatographed and stained with Dragendorff's reagent for confirmatory qualitative analysis for alkaloids. Results showed that oral pre-treatment with 200 mg/kg of HU e , HU b and HU m resulted in a significant (p<0.05, p<0.001) time dependent hypoglycaemic effect, with the butan-1-ol fraction HU causing the most significant (p<0.001) hypoglycaemic effect. In the alloxan-induced hyperglycaemic rats, repeated oral treatment with 200 mg/kg of same HU fractions for 5 days resulted in significant (p<0.05) decreases in the fasting blood glucose concentrations with the most significant (p<0.01) antihyperglycaemic effect also recorded for HU b . Similarly, oral pretreatment with 50 mg/kg of HU Af significantly (p<0.05, p<0.01 and p<0.001) attenuated an increase in the post-absorptive glucose concentration at 1 st -6 th h in the alloxan-induced hyperglycaemic OGTT model. In addition, alkaloid was present in most of the separated spots on the TLC plate. In conclusion, results of this study showed that HU contains a relative high amount of alkaloids which could have accounted for the antihyperglycaemic action of HU that was mediated via intestinal glucose uptake inhibition.
Key words:Hunteria umbellata aqueous seed extract, Alkaloid fraction, Intestinal glucose uptake inhibition, Normal and alloxan-induced hyperglycaemic rats List of Abbreviations: C 4 H 9 OH = butan-1-ol; dH 2 O = distilled water; HCl = hydrochloric acid; HU = aqueous seed extract of Hunteria umbellata (K. Schum.) Hallier f.; HU Af = alkaloid fraction of HU ; HU b = butan-1-ol fraction of HU; HU c = chloroform fraction of HU; HU e = ethyl acetate fraction of HU; HU m = "residue" fraction of HU; Na 2 CO 3 = sodium bicarbonate; NH 4 OH = ammonium hydroxide; R f = retention factor ; TLC = thin layer chromatography; UV = ultraviolet light