Endocrine Abstracts

We have previously attributed the hypoglycaemic effects of Syzygium cordatum leaf extract to crude ethyl acetate extract solubles (EAS) containing triterpenoid compounds. The present study was designed to isolate and characterize triterpene components EAS and investigate the antihyperglycaemic effects alone or in combination with insulin in non-diabetic and streptozotocin (STZ)-induced diabetic rats. EAS soluble extracts were obtained after defatting the S. cordatum leaves with hexane followed by dichloromethane before maceration with ethyl acetate. Column chromatography on silica gel using n-hexane-ethyl acetate yielded mixtures of oleanolic acid, ursolic acid, methyl maslinate and methyl corosolate. Oleonolic acid (OA) was obtained by recrystallisation and its structure was determined by ¹H- and ¹³C-NMR spectroscopy. Oral glucose tolerance test (OGTT) responses were monitored in separate groups of non-diabetic and STZ-induced diabetic rats given glucose load after 18-h fast, followed by various OA doses (40, 80 and 120 mg/kg, p.o.). Rats treated with deionized water (3 ml/kg, p.o.), or insulin (200 μg/kg, s.c) acted as untreated and treated positive controls, respectively. The influence of OA on insulin-induced OGTT responses were studied in separate groups of animals that were treated with combined OA (40 or 80 mg/kg) and insulin (100 or 200 μg/kg, s.c.). Blood glucose was monitored at 15-min intervals for the first hour, and hourly thereafter for 3h. All doses of OA as well as insulin significantly (P<0.05) decreased blood glucose concentrations of non-diabetic and STZ-induced diabetic rats. More notable, however, were the dramatic hypoglycaemic effects produced by combined OA and insulin administration. Compared with rats separately administered with insulin or OA, blood glucose concentrations were significantly (P<0.05) lower at all the time points that blood was sampled in animals treated with combined OA and insulin. We suggest that OA may be useful as adjuvant treatment to enhance insulin effects in diabetes mellitus management.