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1Skeletal Muscle Research Laboratory, School of Medical Sciences, Royal Melbourne Institute of Technology University, Bundoora, 3083, Victoria, Australia; and 2The Copenhagen Muscle Research Center, and Departments of 3Anesthesiology and 4Infectious Diseases, The University of Copenhagen, DK-2100, Copenhagen Ø, Denmark
Submitted 2 May 2003 ; accepted in final form 9 September 2003
To examine the effect of attenuated epinephrine and elevated insulin on intramuscular hormone sensitivity lipase activity (HSLa) during exercise, seven men performed 120 min of semirecumbent cycling (60% peak pulmonary oxygen uptake) on two occasions while ingesting either 250 ml of a 6.4% carbohydrate (GLU) or sweet placebo (CON) beverage at the onset of, and at 15 min intervals throughout, exercise. Muscle biopsies obtained before and immediately after exercise were analyzed for HSLa. Blood samples were simultaneously obtained from a brachial artery and a femoral vein before and during exercise, and leg blood flow was measured by thermodilution in the femoral vein. Net leg glycerol and lactate release and net leg glucose and free fatty acid (FFA) uptake were calculated from these measures. Insulin and epinephrine were also measured in arterial blood before and throughout exercise. During GLU, insulin was elevated (120 min: CON, 11.4 ± 2.4, GLU, 35.3 ± 6.9 pM, P < 0.05) and epinephrine suppressed (120 min: CON, 6.1 ± 2.5, GLU, 2.1 ± 0.9 nM; P < 0.05) compared with CON. Carbohydrate feeding also resulted in suppressed (P < 0.05) HSLa relative to CON (120 min: CON, 1.71 ± 0.18, GLU, 1.27 ± 0.16 mmol·min-1·kg dry mass-1). There were no differences in leg lactate or glycerol release when trials were compared, but leg FFA uptake was lower (120 min: CON, 0.29 ± 0.06, GLU, 0.82 ± 0.09 mmol/min) and leg glucose uptake higher (120 min: CON, 3.16 ± 0.59, GLU, 1.37 ± 0.37 mmol/min) in GLU compared with CON. These results demonstrate that circulating insulin and epinephrine play a role in HSLa in contracting skeletal muscle.
fat metabolism; substrate flux; exercise
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