The novel antihyperglycaemic action of hunteria umbellata seed fractions mediated via intestinal glucose uptake inhibition

The present study is designed at separating and evaluating the antihyperglycaemic and mechanism(s) 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 into its fractions using chloroform, acetyl acetate and butan-1-ol to give chloroform fraction (HUc), ethyl acetate fraction (HUe), butanol fraction (HUb) and the “marc“ (HUm). 200mg/kg of each fraction dissolved in 5% Tween 20 were investigated for their acute and repeated dose oral antihyperglycaemic effects in normal and alloxan-induced hyperglycaemic rats, respectively. 50mg/kg of HU total alkaloid fraction (HUAf) was also evaluated for its possible antihyperglycaemic activity in alloxan-induced hyperglycaemic rats using oral glucose tolerance test (OGTT). Using distilled water-butanol-ammonium hydroxide (2:15:1, v/v/v) solvent system HUb was chromatographed on silica gel-coated aluminium TLC and stained with Dragendorff's reagent for confirmatory qualitative analysis for alkaloids. Results showed that oral pre-treatment with 200mg/kg of HUe, HUb and HUm resulted in a significant (p<0.001) time dependent hypoglycaemic effect, with HUb causing the most significant (p<0.001) hypoglycaemic effect in normal and alloxan-induced hyperglycaemic rats. Also, pre-treatment of alloxan-induced hyperglycaemic rats with 50mg/kg of HUAf caused significant (p<0.001) time dependent decreases in the post-absorptive glucose concentration within the 1st to 6th h post-absorption. In addition, there was presence of alkaloids in a large number of separated spots on TLC plate. Overall, it can be concluded that HUAf accounts for the extract's antihyperglycaemic action which was mediated via intestinal glucose uptake inhibition.