Differences between the effects of adrenaline and noradrenaline on insulin secretion in the dog

The effects of adrenaline and noradrenaline infusions on pancreaticoduodenal venous insulin output were studied in anaesthetized normal dogs. Two experimental protocols were used. In the first, the dogs had a normal blood glucose level at the start of the catecholamine infusion (normoglycaemic dogs). In the second, the animals were made hyperglycaemic by a continuous glucose infusion (hyperglycaemic dogs). In the normoglycaemic dogs, adrenaline (0.5 micrograms X kg-1 X min-1) provoked hyperglycaemia accompanied by an increase in insulin output. Noradrenaline (0.5 micrograms X kg-1 X min-1) also caused an increase in insulin output but without any significant change in blood glucose. In hyperglycaemic dogs, adrenaline (2 micrograms X kg-1 X min-1) reduced the insulin response and enhanced the hyperglycaemia; noradrenaline (2 micrograms X kg-1 X min-1) markedly increased the insulin response (+ 2250%) without any significant change in blood glucose. Propranolol (0.3 mg/kg, IV) prevented the increase of insulin induced by noradrenaline. These findings show that, in the normal dog, adrenaline and noradrenaline infusions can produce opposite effects on insulin response depending on the experimental conditions.