The effect of intensive physical exercise upon plasma levels of pancreatic glucagon was investigated in dogs and in man. In 7 dogs, treadmill exercise until collapse was invariably associated with a rise in plasma glucagon, which at the time of collapse averaged 426 pg/ml (SEM ± 71), more than 4 times the baseline average of 111 pg/ml (SEM ± 26) (p < 0.005). Glucose rose in parallel from 88 mg/100 ml prior to exercise (SEM ± 2) to a peak of 105 mg/100 ml (SEM =fc 4) at collapse (p < 0.01). Hypoglycemia did not occur in any dog. Insulin remained unchanged but rose briefly soon after collapse. In 4 human volunteers exercised to exhaustion on a stationary bicycle glucagon rose from 68 pg/ml (SEM ± 17) to 116 pg/ml (SEM ± 14) 10 min after the exhaustion point (p < 0.02), and again glucose rose in parallel from a pre-exercise value of 93 mg/100 ml (SEM ± 3) to 124 mg/100 ml (SEM ± 8) during recovery. Insulin also rose during recovery. When dogs were exercised to collapse during a 15 mg/kg/min intravenous glucose infusion begun 1 hr before the start of exercise, glucagon, which had been suppressed by the hyperglycemia to 57 pg/ml (SEM ± 2 2) before exercise, rose to a peak of only 160 pg/ml (SEM ± 49) (p < 0.02) at the time of collapse, significantly less than the peak of 426 pg/ml (p < 0.02) in the normoglycemic dogs; insulin, which had been increased to 100 µU/ml (SEM ± 24) by the hyperglycemia, declined to 23 µU/ml (SEM ± 3.6) during exercise; glucose declined 75 mg/100 ml (SEM ± 13) initially, but rose 38 mg/100 ml (SEM =t 7) prior to collapse. In dogs fasted for 48 hr and 96 hr, the patterns of the precollapse hyperglucagonemia and hyperglycemia did not differ significantly from the control dogs. The results indicate that this type of exercise is an extremely powerful stimulus of glucagon secretion in dogs and, perhaps to a lesser degree in man. They indicate that the effect of this type of exercise on the alpha cell is not the result of hypoglycemia, which does not occur; instead, precollapse hyperglycemia paralleling the hyperglucagonemia is observed, even after starvation. The findings raise the possibility that glucagon plays a physiologic role in meeting the metabolic demands of this form of exercise.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism
- Clinical Biochemistry
- Biochemistry, medical