Rats subjected to forced swimming with a tail weight for 45 minutes exhibited a mean plasma glucagon level of 623 (SEM ± 80) pg/ml, significantly above the 102 (SEM ± 11) pg/ml average of resting control rats (p < 0.001). The administration of the α-adrenergic blocker phentolamine prior to exercise completely blocked exercise-induced hyperglucagonemia. Propranolol treatment, by contrast, failed to alter the rise in glucagon induced by exercise. Although differences in glucose concentration were present in the various groups and undoubtedly influenced the changes, they were not sufficient to account for the findings. It appears, therefore, that under the conditions of these experiments exercise-induced hyperglucagonemia in rats was mediated largely by adrenergic stimulation.
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