Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, C29
The effects of syzygium aromaticum derived oleanolic acid on glucose transport across rat-everted intestinal sacs in vitro
A. Khathi2,1, P. S. Ngubane2,1, B. Masola1,2, C. T. Musabayane2,1
1. Human Physiology, University of KwaZulu-Natal, Durban, KwaZulu-Natal, South Africa. 2. Biochemistry, University of KwaZulu-Natal, Durban, KwaZulu-Natal, South Africa.
The hypoglycaemic effects of Syzygium aromaticum derived triterpene, oleanolic acid (OA) in streptozotocin (STZ)-induced diabetic rats are mediated in part via increased hepatic glycogen synthesis . The wide range of available anti-diabetic suggests that a variety of mechanisms of action are involved in the blood glucose lowering effects. The present study was designed to investigate the effects of OA on glucose transport in vitro using the everted rat intestinal protocol which has been previously described by Mahomoodally et al., 2005.  Everted intestinal sacs from rats filled with 1 ml of Krebs-Henseleit bicarbonate buffer (KHB) were mounted in an organ bath containing 50 ml of the same incubation medium. D-glucose (10 mM) was added to the medium just before the start of the appropriate experiments. In separate preparations graded concentrations of either OA (0.375-3.00 mM) or the standard drug, phlorizin (10-6 - 10-3 M) were incubated for 30 min in in the mucosal bathing fluid containing glucose (10 mM) to investigate effects on glucose transport across the intestine gut wall. The external incubation medium will be continuously bubbled with gas mixture of 95% oxygen) and 5% carbon dioxide during the whole incubation period. The organ bath was surrounded by a water jacket maintained at 37-40 °C. The transport of D-glucose was evaluated by measuring the increase in glucose concentration inside the intestinal sacs after 30 min of incubation. The change in glycogen concentration in the gut wall was interpreted as assessed glucose metabolized. Graph Pad Instat software (version 4) using one way analysis of variance (ANOVA) followed by Turkey- Kramer multiple comparison test was used. P values < 0.05 were considered significant. Lower concentration (0.375 and 0.750 mM) of OA significantly inhibited (p < 0.05) D-glucose transport across the rat everted intestinal sac in a dose-dependent manner whereas the inhibitory effects of higher concentrations of 0.750, 1.500 and 3.000 mM could not be statistically separated. Phlorizin, however, exhibited dose-dependent inhibition of glucose uptake across the everted intestinal sac. The accumulation of glycogen concentration in the gut wall increased significantly in the presence of OA. The fate of glucose retained within intestinal wall is difficult to quantify since glucose is rapidly metabolized by enterocytes. We hypothesize that OA inhibits the active transport of d-glucose suggesting that the triterpene can be a potential alternative drug therapy of postprandial hyperglycaemia via inhibition of glucose uptake across the small intestine.
Where applicable, experiments conform with Society ethical requirements