Effects of glucagon, glucose, adrenaline and insulin infusion on blood glucose level in the common African toad (bufo regularis).

Male toads, weighing 70-123 g, were divided into 13 groups with 8 toad in each group. Animals in each group were fasted overnight before the experiments. Toads in groups 1 to 4 were infused for 30 minutes with adrenaline, 5 ugkg-1 min-1, glucose, 5.5 mg kg-1 min-1; glucagon 2 ugkg-1 min-1; and insulin 2000 uU kg-1 min-1, respectively. Blood samples for blood glucose measurement were taken before, during and after each infusion. The experiment was repeated in groups 5 and 6 using 3.5 mg kg-1 min-1 and 7.5 mg kg-1 min-1 of glucose respectively. Toads in groups 7 to 9 were pretreated with prazosin, 0.2 mg/kg and those in groups 10 to 12 were pretreated with propranolol, 0.5 mg/kg. After pretreatment, glucose, glucagon and insulin infusions were repeated in the alpha-blocked and beta-blocked toads, respectively. Group 13 was infused with 0.7% saline and served as the control. The results showed that infusions of adrenaline, glucose and glucagon resulted in significant hyperglycaemia while insulin caused hypoglycaemia. The hyperglycaemic response to glucose was dose-dependent. The experiments using blockers showed that the glycaemic effects of glucagon and insulin are mediated via beta adrenoceptors, that for glucose is via alpha adrenoceptors and from an earlier study, the glycaemic response of adrenaline is through both alpha and beta adrenoceptors.