Inhibition of hepatic neoglucogenesis and glucose‐6‐phosphatase by aqueous extract of Bauhinia megalandra leaves

An aqueons extract of Bauhinia megalandra leaves causes a decrease of nearly 50% in the glucose production, from lactate or fructose, of rat liver slices incubated in Krebs‐Ringer bicarbonate buffer supplemented with oleate‐saturated albumin. In intact microsomes, the B. megalandra extract acts as a mixed non‐competitive inhibitor of glucose‐6‐phosphatase. In the histone‐disrupted microsomes the extract has no effect on glucose‐6‐phosphate hydrolysis. However in the presence of the extract, glucose‐6‐phosphatase activity was linear with time, as in the control, but at a lower level, reaching a plateau after 20 min. This suggests an inhibition of the catalytic subunit by accumulation of orthophosphate and/or glucose, as a consequence of the inhibition of its translocases (T2 and/or T3 respectively). Neither the intact nor the disrupted microsomal pyrophosphatase kinetics parameters were affected by the inclusion of the leaf extract. The above results strongly suggest that the main effect of the B. megalandra extract is the inhibition of the glucose‐6‐phosphate transporter (T1) of the microsomal glucose‐6‐phosphatase system; however, an inhibition of T3 was not ruled out. The glucose‐6‐phosphatase inhibition might explain the decrease in the liver slices neoglucogenic capacity and in turn could reduce glucose levels in diabetic patients. © 1998 John Wiley & Sons, Ltd.