title: Blood flow, lipid oxidation, and muscle glycogen synthesis after glycogen depletion by strenuous exercise.
abstract: We studied the interrelationship between blood flow, glycogen synthesis, and glucose and lipid utilization in 14 healthy men. A 4-h euglycemic insulin clamp with indirect calorimetry and muscle biopsies were done after a glycogen depletion (exercise) and after a resting day (control). In spite of the exercise induced decrease in leg muscle glycogen content (28% in the basal state, 22% after hyperinsulinemia, P < 0.05 in both as compared with the control study), basal or insulin stimulated glycogen synthase activity remained unchanged. In the basal state, glucose oxidation was 54% lower (P < 0.001) and lipid oxidation 108% higher (P < 0.001) after the glycogen depletion as compared with that in the control study. During the post-depletion insulin clamp, the glucose oxidation rate was 17% lower (P < 0.02) and lipid oxidation 169% higher (P < 0.01), while the whole body total glucose disposal was similar in both studies. Baseline forearm blood flow was similar and increased equally by over 40% during both insulin clamp studies (P < 0.05). Basal glucose extraction after glycogen depletion study was one third of that in the control study (P < 0.05). Both basal and insulin stimulated leg muscle glycogen content correlated inversely with basal forearm blood flow (r = -0.69, P < 0.01 and r = -0.82, P < 0.001, respectively) and basal lipid oxidation (r = -0.54, P < 0.05 and r = -0.64, P < 0.01, respectively) after glycogen depletion. Basal glycogen synthase fractional activity correlated positively with forearm blood flow (r = 0.78, P < 0.001) and forearm glucose uptake (r = 0.71, P < 0.05) during the insulin infusion.
  
  
  CONCLUSIONS
  1) the unchanged insulin sensitivity in the face of glycogen depletion is probably a result of increased lipid oxidation, and 2) blood flow is related inversely to muscle glycogen content and directly to glycogen synthase activity.
authors.affiliation: Department of Medicine, Helsinki University Central Hospital, Finland. juha.tuominen@helsinki.fi
authors.forename: J A
authors.initials: JA
authors.lastname: Tuominen
authors.forename: J E
authors.initials: JE
authors.lastname: Peltonen
authors.forename: V A
authors.initials: VA
authors.lastname: Koivisto
mesh_terms: D000328:Adult; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005542:Forearm / Q000502:physiology; D005947:Glucose / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism*; D006006:Glycogen Synthase / Q000502:physiology; D006801:Humans; D007328:Insulin; D007866:Leg / Q000502:physiology; D050356:Lipid Metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply / Q000502:physiology*; D010084:Oxidation-Reduction; D012039:Regional Blood Flow
chemical_list: D007328:Insulin; D006003:Glycogen; D006006:Glycogen Synthase; D005947:Glucose