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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Adrenergic regulation of HSL serine phosphorylation and activity in human skeletal muscle during the onset of exercise

¹Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada; ²St. Vincent's Institute and Department of Medicine, University of Melbourne, Fitzroy, Victoria, Australia; and ³Department of Medicine, McMaster University, Hamilton, Ontario, Canada

Submitted 22 February 2006 ; accepted in final form 2 May 2006

Skeletal muscle hormone-sensitive lipase (HSL) activity is increased by contractions and increases in blood epinephrine (EPI) concentrations and cyclic AMP activation of the adrenergic pathway during prolonged exercise. To determine the importance of hormonal stimulation of HSL activity during the onset of moderate- and high-intensity exercise, nine men [age 24.3 ± 1.2 yr, 80.8 ± 5.0 kg, peak oxygen consumption (O_{2 peak}) 43.9 ± 3.6 ml·kg^–1·min^–1] cycled for 1 min at 65% O_{2 peak}, rested for 60 min, and cycled at 90% O_{2 peak} for 1 min. Skeletal muscle biopsies were taken pre- and postexercise, and arterial blood was sampled throughout exercise. Arterial EPI increased (P < 0.05) postexercise at 65% (0.45 ± 0.10 to 0.78 ± 0.27 nM) and 90% O_{2 peak} (0.57 ± 0.34 to 1.09 ± 0.50 nM). HSL activity increased (P < 0.05) following 1 min of exercise at 65% O_{2 peak} [1.05 ± 0.39 to 1.78 ± 0.54 mmol·min^–1·kg dry muscle (dm)^–1] and 90% O_{2 peak} (1.07 ± 0.24 to 1.91 ± 0.62 mmol·min^–1·kg dm^–1). Cyclic AMP content also increased (P < 0.05) at both exercise intensities (65%: 1.52 ± 0.67 to 2.75 ± 1.12, 90%: 1.85 ± 0.65 to 2.64 ± 0.93 µmol/kg dm). HSL Ser660 phosphorylation (55% increase) and ERK1/2 phosphorylation (33% increase) were augmented following exercise at both intensities, whereas HSL Ser563 and Ser565 phosphorylation were not different from rest. The results indicate that increases in arterial EPI concentration during the onset of moderate- and high-intensity exercise increase cyclic AMP content, which results in the phosphorylation of HSL Ser660. This adrenergic stimulation contributes to the increase in HSL activity that occurs in human skeletal muscle in the first minute of exercise at 65% and 90% O_{2 peak}.

hormone-sensitive lipase; arterial epinephrine concentration; cyclic adenosine 5'-monophosphate; serine 660 phosphorylation; extracellular regulated kinase 1/2 phosphorylation

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