Insulin does not influence muscle glycogenolysis in adrenodemedullated exercising rats.
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.
Yang
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HT
Department of Zoology, Brigham Young University, Provo, Utah 84602.
Carlson
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Winder
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WW
D000313:Adrenal Medulla / Q000502:physiology*; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D004837:Epinephrine / Q000097:blood / Q000494:pharmacology; D006003:Glycogen / Q000378:metabolism*; D007328:Insulin / Q000097:blood*; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D008112:Liver Glycogen / Q000378:metabolism; D008297:Male; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000097:blood; D005082:Physical Exertion; D051381:Rats; D011919:Rats, Inbred Strains
D001786:Blood Glucose; D007328:Insulin; D007773:Lactates; D008112:Liver Glycogen; D019344:Lactic Acid; D006003:Glycogen; D009638:Norepinephrine; D004837:Epinephrine