Endocrine Abstracts

Previous studies from our laboratories indicate that the anti-diabetic effects of Syzygium cordatum (Hochst.) (Myrtaceae) leaf extract in streptozotocin-induced diabetic rats may be attributed in part to mixtures of triterpenes, oleanolic acid (OA) and ursolic acid (UA). For the bioactive compounds to have potential in diabetes management, they should also alleviate or prevent complications of diabetes mellitus; kidney function and cardiovascular disorders. This study investigated assess whether S. cordatum leaf derived OA influenced renal function of streptozotocin (STZ-induced diabetic rats evaluated by the ability to increase urinary Na⁺ outputs parameters and creatinine clearance (Ccr). Extraction and fractionation of S. cordatum powdered leaf ethyl acetate-solubles (EAS) yielded mixtures of OA/UA and methyl maslinate/methyl corosolate. Recrystallisation of OA/UA mixture using ethanol afforded OA whose structure was confirmed by NMR spectroscopy (¹H & ¹³C). Acute effects of OA on kidney function and mean arterial blood pressure (MAP) were investigated in anaesthetized rats challenged with hypotonic saline after a 3.5-h equilibration for 4 h of 1 h control, 1.5 h treatment and 1.5 h recovery periods. OA was added to the infusate during the treatment period. Chronic effects of OA were studied in individually-caged rats treated twice daily with OA (60 mg/kg, p.o.) for 5 weeks. By comparison with respective control animals administrations OA significantly increased Na⁺ excretion rates of non-diabetic and STZ-induced diabetic rats without affecting urine flow, K⁺ and Cl⁻ rates. By comparison with respective control animals, subchronic administrations of OA significantly (P<0.05) increased GFR in non-diabetic (2.88±0.14 vs 3.71±0.30 ml/min) and STZ-diabetic rats (1.81±0.32 vs 3.07±0.16 ml/min, n=6 in all groups) with concomitant reduction of plasma creatinine concentration. OA also caused significant decreases in MAP in non-diabetic and STZ-induced diabetic rats. These findings suggest that OA may have beneficial effects on some processes associated with renal derangement of STZ-induced diabetic rats.