Hyperglycaemic effect of glucagon after prolonged exhausting exercise in dogs

The purpose of this work was to compare the hyperglycaemic effect of glucagon at rest and after prolonged exhausting exercise in dogs. The following doses of glucagon were administered in 10-minute i.v. infusions: 0.1, 0.5, 1.0 micgrogram-kg-1 min-1. Significant differences were demonstrated in the blood glucose level after glucagon administration in doses of 0.1 and 0-5 microgram-kg-1 min-1 at rest as well as after exercise, and glucagon-induced hyperglycaemia was always lower after exercise than at rest. Increasing of glucagon dose from 0.5 to 1.0 microgram-kg-1 min-1 was not followed by a similar increase of the hyperglycaemic response. In additional experiments glucagon was administered together with adrenaline using two combinations of doses: 0.1 micron g-kg-1min-1 of glucagon and 0.25 microgram-kg-1 min-1 of adrenaline or 1.0 microgram-kg-1 min-1 of glucogen and 1.0 microgram-kg-1 min-1 of adrenaline. The hyperglycaemic effects of glucagon and adrenaline were additive at rest and after exercise when low doses of both hormones were used. After prolonged exercise this additive effect was not found when the "saturating" doses of glucagon and adrenaline were used (1.0 microgram-kg-1 min-1). The results obtained suggest that the hyperglycaemic response to glucagon is decreased in dogs after prolonged excise. It seems that this can be partly explained by the changed reactivity of hepatic tissue to this horme after prolonged exercise.