Journal of Applied Physiology, Vol 72, Issue 5 1991-1998, Copyright © 1992 by American Physiological Society
Insulin-induced hypoglycemia in fed and fasted exercising rats
J. Arogyasami, T. L. Sellers, G. I. Wilson, J. P. Jones, C. Duan and W. W. Winder
Zoology Department, Brigham Young University, Provo, Utah 84602.
To determine running performance and hormonal and metabolic responses
during insulin-induced hypoglycemia, fed and fasted male rats (315 +/- 3 g)
were infused with insulin (100 mU/ml, 1.5 ml/h) or saline (1.5 ml/h) for 60
min and then killed at rest or after running on the treadmill (21 m/min,
15% grade). Insulin-infused fed rats ran poorly during the second 10 min of
a 20-min exercise test. They were capable of running a total of 43 +/- 5
min, compared with 138 +/- 6 min for saline-infused fed rats. Fasted
insulin-infused rats were able to run only 12.8 +/- 0.8 min, compared with
122 +/- 15 min for fasted saline-infused rats. In fasted rats, blood
glucose was 1.6 +/- 0.1 mM after 60 min of insulin infusion and 1.2 +/- 0.1
mM after running to exhaustion. Artificial increase of plasma free fatty
acids had no effect on performance. Intravenous infusion of glucose at the
time of fatigue produced an immediate recovery, allowing the formerly
fatigued rats to run 20 min without development of fatigue. These results
provide evidence that severe hypoglycemia can be a significant cause of
fatigue, even if it occurs early in the course of an exercise bout.
