Metabolic and hormonal responses in theophylline-increased cold resistance in males.
The effects of theophylline (a phosphodiesterase inhibitor-adenosine receptor antagonist) and substrate feeding (Ensure, 250 kcal/235 ml) on cold resistance were studied in seminude males undertaking submaximal (50% maximum O2 consumption), intermittent (34% of total time) exercise in the cold (-5 to 15 degrees C, individually adjusted) for 3 h. Each subject (n = 7) served as his own control and was tested on a weekly schedule. Under control treatment, rectal temperature (Tre) decreased by 0.9 degrees C to approximately 36.2 degrees C after cold exposure, whereas under theophylline and Ensure, the decrease of Tre was only 0.4 degrees C, indicating a significant increase (P less than 0.05) in cold resistance (50% better than control). The plasma concentration of theophylline was 4.8-5.9 micrograms/ml and was positively correlated with plasma concentration of free fatty acids. Plasma norepinephrine (NE) increased significantly during cold exposure; the absolute concentration was significantly higher after theophylline pretreatment. The plasma concentrations of glucose, epinephrine, cortisol, and adenosine 3',5'-cyclic monophosphate did not change and the changes of free thyroxine and triiodothyronine were minor. Together, the effectiveness of theophylline + Ensure in acutely increasing cold resistance may be due to increased substrate availability for thermogenesis, part of which, through theophylline's potentiation of both sympathetic release of NE and NE-stimulated lipolysis and part of which, through supplementary feeding of Ensure.
Wang
L C
LC
Department of Zoology, University of Alberta, Edmonton, Canada.
Man
S F
SF
Belcastro
A N
AN
D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D001831:Body Temperature; D001833:Body Temperature Regulation / Q000187:drug effects*; D002395:Catecholamines / Q000097:blood; D003080:Cold Temperature; D004734:Energy Metabolism; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006339:Heart Rate; D006728:Hormones / Q000097:blood*; D006801:Humans; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D008297:Male; D012007:Rectum; D013806:Theophylline / Q000097:blood / Q000494:pharmacology*
D001786:Blood Glucose; D002395:Catecholamines; D005230:Fatty Acids, Nonesterified; D006728:Hormones; D007773:Lactates; D019344:Lactic Acid; D013806:Theophylline