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1 Skeletal Muscle Research Laboratory, School of Medical Sciences, RMIT University, Bundoora, Vic, Australia
2 The Copenhagen Muscle Research Centre, The University of Copenhagen, Copenhagen, Copenhagen, Denmark
3 The Copenhagen Muscle Research Centre, The University of Copenhagen, Copenhagen, Copenhagen, Denmark; Department of Anesthesiology, The University of Copenhagen, Copenhagen, Copenhagen, Denmark
4 The Copenhagen Muscle Research Centre, The University of Copenhagen, Copenhagen, Copenhagen, Denmark; Department of Infectious Diseases, The University of Copenhagen, Copenhagen, Copenhagen, Denmark
5 Skeletal Muscle Research Laboratory, School of Medical Sciences, RMIT University, Bundoora, Vic, Australia; The Copenhagen Muscle Research Centre, The University of Copenhagen, Copenhagen, Copenhagen, Denmark
* To whom correspondence should be addressed. E-mail: mark.febbraio{at}rmit.edu.au.
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 semi-recumbent cycling (60% VO2 peak) 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 analysed for HSLa. Blood samples were simultaneously obtained from a brachial artery and a femoral vein prior to 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. The hormones 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) when 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/kg dm). There were no differences in leg lactate or glycerol release when comparing trials, 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.
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