Endocrine Abstracts

The wide range of phytochemicals in medicinal plants serves as sources of bioactive compounds for treatment diabetic complications. We investigated whether Syzygium aromaticum-isolated oleanolic acid (OA) has beneficial effects on some diabetic complications in STZ-induced diabetic rats. We used experimental models of hypertension [spontaneously hypertensive (SHR) and Dahl salt-sensitive (DSS)] rats to explore the effects of OA on mean arterial blood pressure (MAP) and renal function. Selected biochemical parameters were also assessed in blood, muscle and liver samples from diabetic rats treated with OA for 5 weeks. The effects of a 9-week OA administration on MAP and kidney function were monitored in normotensive Wistar, SHR and DSS rats. In addition, anti-oxidative effects of OA on cardiac, hepatic and renal tissues were examined in all groups. Renal proximal tubular effects of OA on Na⁺ handling were studied in anaesthetized Wistar 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 using lithium clearance. OA was added to the infusate during the treatment period. Untreated diabetic rats exhibited hyperglycaemia, oxidative stress, depleted hepatic and muscle glycogen concentrations which were restored to near normalcy by OA treatment. OA administration elicited hypotensive responses in all groups of animals which were more marked in hypertensive animals and correlated positively with increased urinary Na⁺ excretion. Acute infusion OA increased FE_Na and FE_Li without influencing GFR indicating that at least part of the overall natriuretic effect involved inhibition of Na⁺ reabsorption in the proximal tubule. OA treatment reduced malondialdehyde (a marker of lipid peroxidation) and increased activities of antioxidant enzymes; superoxide dismutase and glutathione peroxidase in hepatic, cardiac and renal tissues in all groups. These results suggest that the hypoglycaemic and antioxidant effects of OA improve some metabolic complications of diabetes.