Effect of various doses of cocaine on endurance capacity in rats.
To determine the effects of a variety of doses of cocaine on endurance capacity, rats were injected intraperitoneally with either 0.1, 0.5, 2.5, 12.5, or 20 mg/kg body wt 20 min before running to exhaustion at 26 m/min up a 10% grade. Animals given saline ran 116 +/- 9 (SE) min. At doses of 12.5 and 20 mg/kg, cocaine reduced endurance time significantly (34 and 74%, respectively). At rest the drug had no effect on liver or fast-twitch muscle glycogen but significantly reduced (20-40%) soleus glycogen at the two highest doses. However, at exhaustion, the quantity of glycogen depleted in the fast-twitch red and white vastus muscles was similar in all groups despite the reduced run times of the animals receiving a higher dose implying a greater rate of glycogenolysis due to cocaine. Blood lactate in the 20 mg/kg group (9.9 +/- 1.2 mM) at exhaustion was nearly twice that of the saline controls at exhaustion (5.1 +/- 0.6). Before exercise plasma norepinephrine (at doses of 2.5, 12.5 and 20 mg/kg) was higher than saline controls and remained higher (20 mg/kg groups) at exhaustion. We conclude that high doses of cocaine cause rapid muscle glycogen depletion and early fatigue. The mechanism by which cocaine causes these effects is not clear.
Bracken
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ME
Department of Physical Education, Brigham Young University, Provo, Utah 84602.
Bracken
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DR
Winder
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Conlee
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RK
D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D002395:Catecholamines / Q000097:blood; D003042:Cocaine / Q000494:pharmacology*; D003345:Corticosterone / Q000097:blood; D004305:Dose-Response Relationship, Drug; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006003:Glycogen / Q000378:metabolism; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D008099:Liver / Q000378:metabolism; D008297:Male; D009132:Muscles / Q000378:metabolism; D010187:Pancreatic Hormones / Q000097:blood; D010807:Physical Endurance / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains
D001786:Blood Glucose; D002395:Catecholamines; D005230:Fatty Acids, Nonesterified; D007773:Lactates; D010187:Pancreatic Hormones; D019344:Lactic Acid; D006003:Glycogen; D003042:Cocaine; D003345:Corticosterone