AJP - Regulatory, Integrative and Comparative Physiology, Vol 253, Issue 4 535-R540, Copyright © 1987 by American Physiological Society
Insulin does not influence muscle glycogenolysis in adrenodemedullated exercising rats
H. T. Yang, K. I. Carlson and W. W. Winder
Department of Zoology, Brigham Young University, Provo, Utah 84602.
Previous reports have indicated that adrenodemedullated (ADM) rats exhibit
an impairment in muscle glycogenolysis and elevated plasma insulin during
exercise. This study was designed to determine whether the impaired muscle
glycogenolysis in ADM rats is due to absence of epinephrine or to the
inappropriately elevated plasma insulin. Fasted ADM rats were infused with
saline, with epinephrine (0.045 micrograms . 100 g-1 . min-1), or with
epinephrine + insulin (1.6, 3.3, 6.6, and 8.3 ng . 100 g-1 . min-1) during
a 30-min run on the treadmill (21 m/min, 10% grade). Soleus muscle glycogen
decreased from 5.1 +/- 0.2 mg/g in resting ADM rats to 4.0 +/- 0.2, 0.8 +/-
0.1, and 0.8 +/- 0.1 mg/g in the exercising saline-, epinephrine-, and
epinephrine + insulin (8.3 ng . 100 g-1 . min-1)-infused rats,
respectively. Glycogen utilization in gastrocnemius and red and white
quadriceps muscles during exercise was likewise unaffected by insulin
infusion. Blood glucose concentrations were 3.75 +/- 0.08, 2.65 +/- 0.14,
3.93 +/- 0.20, and 2.03 +/- 0.09 mM in the same groups at the end of
exercise. Blood lactate was 50% lower and the blood 3-hydroxybutyrate and
plasma free fatty acid concentrations were significantly higher in the ADM
+ saline rats than the other exercising rats. We conclude that
inappropriately elevated plasma insulin does not impair
epinephrine-stimulated muscle glycogenolysis in fasted ADM rats during
exercise.
