Antihyperglycaemic and antiperoxidative roles of acarbose in type 2 diabetes mellitus are possibly mediated through changes in thyroid function.

1. The aim of the present study was to reveal the possible involvement of thyroid hormones in the antihyperglycaemic and antiperoxidative effects of acarbose. 2. The effects of acarbose on changes in serum concentration of thyroid hormones, insulin and glucose in dexamethasone-induced type 2 diabetic mice were investigated. Simultaneously, changes in lipid peroxidation (LPO), reduced glutathione (GSH) content and the activity of associated endogenous anti-oxidant enzymes, such as superoxide dismuatase (SOD) and catalase (CAT), were investigated in renal and cardiac tissues, which are commonly affected in diabetes mellitus. 3. Although administration of dexamethasone (1.0 mg/kg, i.m., for 22 days) caused hyperglycaemia with a parallel increase in serum insulin and tissue LPO, it decreased thyroid hormone concentrations and the activity of SOD and CAT. 4. When dexamethasone-induced hyperglycaemic mice were treated with acarbose (10 mg/kg per day, p.o., for 15 days), levels of thyroid hormones were increased and most of the abnormalities, including serum insulin and glucose levels, tissue LPO, SOD and CAT activity and GSH content, were reversed. 5. These findings suggest the involvement of thyroid hormones in the mode of action of acarbose in amelioration of type 2 diabetes mellitus.