title: Interstitial glycerol concentrations in human skeletal muscle and adipose tissue during graded exercise.
abstract: OBJECTIVE
  It is not clear how lipolysis changes in skeletal muscle and adipose tissue during exercise of different intensities. We aimed at estimating this by microdialysis and muscle biopsy techniques.
  
  
  METHODS
  Nine healthy, young men were kicking with both legs at 25% of maximal power (Wmax) for 45 min and then simultaneously with one leg at 65% and the other leg at 85% Wmax for 35 min.
  
  
  RESULTS
  Glycerol concentrations in skeletal muscle and adipose tissue interstitial fluid and in arterial plasma increased (P<0.001) during low intensity exercise and increased (P<0.05) even more during moderate intensity exercise. The difference between interstitial muscle and arterial plasma water glycerol concentration, which indicates the direction of the glycerol flux, was positive (P<0.05) at rest (21 +/- 9 microM) and during exercise at 25% Wmax (18 +/- 6 microM). The difference decreased (P<0.05) with increasing exercise intensity and was not significantly different from zero during exercise at 65% (-11 +/- 17 microM) and 85% (-12 +/- 13 microM) Wmax. In adipose tissue, the difference between interstitial and arterial plasma water glycerol increased (P<0.001) with increasing intensity. The net triacylglycerol breakdown, measured chemically from the biopsy, did not differ significantly from zero at any exercise intensity although directional changes were similar to microdialysis changes.
  
  
  CONCLUSIONS
  Skeletal muscle releases glycerol at rest and at low exercise intensity but not at higher intensities. This can be interpreted as skeletal muscle lipolysis peaking at low exercise intensities but could also indicate that glycerol is taken up in skeletal muscle at a rate which is increasing with exercise intensity.
authors.affiliation: Copenhagen Muscle Research Centre, Department of Medical Physiology, The Panum Institute, University of Copenhagen, Copenhagen, Denmark.
authors.forename: B
authors.initials: B
authors.lastname: Stallknecht
authors.forename: B
authors.initials: B
authors.lastname: Kiens
authors.forename: J W
authors.initials: JW
authors.lastname: Helge
authors.forename: E A
authors.initials: EA
authors.lastname: Richter
authors.forename: H
authors.initials: H
authors.lastname: Galbo
mesh_terms: D000273:Adipose Tissue / Q000098:blood supply / Q000378:metabolism*; D000328:Adult; D001706:Biopsy; D002395:Catecholamines / Q000097:blood; D015444:Exercise / Q000502:physiology*; D045604:Extracellular Fluid / Q000378:metabolism; D005990:Glycerol / Q000032:analysis* / Q000097:blood; D006801:Humans; D008066:Lipolysis; D008297:Male; D017551:Microdialysis / Q000379:methods; D018482:Muscle, Skeletal / Q000378:metabolism*; D012039:Regional Blood Flow; D040521:Subcutaneous Tissue / Q000098:blood supply / Q000378:metabolism
chemical_list: D002395:Catecholamines; D005990:Glycerol