Glucose, glucagon, and insulin during adrenergic blockade in exercising sheep

The interrelationships of glucagon and insulin with the sympathetic system on glucose turnover during exercise were examined in sheep. Six sheep were run for 45 min on a treadmill with and without alpha- and/or beta-adrenergic blockade. The exercise-induced increase in glucose appearance, as assessed by infusion of [2-3H]glucose, was reduced during the first 25 min of exercise by phentolamine administration. The metabolic clearance rate of glucose also was greater during exercise with phentolamine treatment than without. Phentolamine was associated with a rise in insulin concentrations and appeared to delay the exercise-induced rise in glucagon. Propranolol administration had no effect on glucose turnover and plasma glucagon and insulin. Nor did it have any effect on the changes in glucose, insulin, or glucagon induced by phentolamine administration. These observations are consistent with the alpha-adrenergic mediation of the sympathetic influences on insulin and glucagon secretion, which may account in part for the glucose adaptations to exercise in sheep. However, direct affects of circulating catecholamines on and increased stimulation of sympathetic innervation to the liver cannot be ruled out.