COMPARISON OF THE EFFECTS OF EFAROXAN AND GLIBENCLAMIDE ON PLASMA-GLUCOSE AND INSULIN LEVELS IN RATS

The effect of efaroxan (1 and 5 mg/kg p.o.; a selective alpha-2-adrenoceptor antagonist) was compared to glibenclamide (1 and 5 mg/kg p.o.; a standard sulphonylurea) on basal plasma glucose levels of fed and fasted rats. In addition, the effect of efaroxan (5 mg/kg p.o.) and glibenclamide (2 or 5 mg/kg p.o.), alone and in combination, on the hyperglycaemia and hyperinsulinaemia induced by glucose challenges, were investigated. An intra-arterial (250 mg/kg i.a.) and a subcutaneous (1 g/kg s.c.) glucose challenge were used to stimulate the fast and slow release phases of insulin secretion. Efaroxan increased plasma insulin levels in both conscious fed and fasted rats without greatly affecting plasma glucose levels. Glibenclamide also elevated insulin levels, hut was associated with marked hypoglycaemia. Efaroxan and glibenclamide potentiated the slow and fast release of insulin secretion, but glibenclamide had a tendency to produce hypoglycaemia in these test situations, a property not shared by efaroxan. A combination of efaroxan and glibenclamide produced a greater elevation in the slow and fast insulin release phases than either compound alone, but did not enhance the hypoglycaemia seen with glibenclamide alone. These results provide further evidence that pancreatic alpha-2-adrenoceptors are involved in the regulation of insulin secretion.