title: Effect of endurance training on hepatic glycogenolysis and gluconeogenesis during prolonged exercise in men.
abstract: In humans, endurance training markedly reduces the rate of hepatic glucose production during exercise. To determine whether this is due to a reduction in glycogenolysis, in gluconeogenesis, or in both processes, six men were studied at rest and during 2 h of cycle ergometer exercise at 60% pretraining peak O2 consumption (VO2peak), both before and after completion of a strenuous endurance training program (cycling at 75-100% VO2peak for 45-90 min/day, 6 days/wk for 12 wk). The overall rate of glucose appearance (Ra) was determined using a primed continuous infusion of [6,6-2H]glucose, whereas the rate of gluconeogenesis (Rgng) was estimated from the incorporation of 13C into glucose (via pyruvate carboxylase) from simultaneously infused [13C]bicarbonate. Training did not affect glucose kinetics at rest but reduced the average Ra during exercise by 42% [from 36.8 +/- 3.8 to 21.5 +/- 3.6 (SE) mumol.min-1.kg-1; P < 0.001]. This decrease appeared to be mostly due to a reduction in hepatic glycogenolysis. However, the estimated Rgng during exercise also decreased significantly (P < 0.001) with training, falling from 7.5 +/- 1.6 mumol.min-1.kg-1 (23 +/- 3% of total Ra) before training to 3.1 +/- 0.6 mumol.min-1.kg-1 (14 +/- 3% of total Ra) after training. These training-induced adaptations in hepatic glucose metabolism were associated with an attenuated hormonal response to exercise (i.e., higher insulin and lower glucagon, norepinephrine, and epinephrine concentrations) as well as a reduced availability of gluconeogenic precursors (i.e., lower lactate and glycerol concentrations). We conclude that endurance training reduces both hepatic glycogenolysis and gluconeogenesis during prolonged exercise in men.
authors.affiliation: Metabolism Unit, Shriners Burns Institute, Galveston 77550.
authors.forename: A R
authors.initials: AR
authors.lastname: Coggan
authors.forename: S C
authors.initials: SC
authors.lastname: Swanson
authors.forename: L A
authors.initials: LA
authors.lastname: Mendenhall
authors.forename: D L
authors.initials: DL
authors.lastname: Habash
authors.forename: C L
authors.initials: CL
authors.lastname: Kien
mesh_terms: D000328:Adult; D000409:Alanine / Q000097:blood; D001786:Blood Glucose / Q000378:metabolism; D002096:C-Peptide / Q000378:metabolism; D004837:Epinephrine / Q000097:blood; D015444:Exercise / Q000502:physiology; D005934:Glucagon / Q000097:blood; D005943:Gluconeogenesis; D005990:Glycerol / Q000097:blood; D006003:Glycogen / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000097:blood; D007700:Kinetics; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D008099:Liver / Q000378:metabolism*; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010101:Oxygen Consumption; D010807:Physical Endurance
chemical_list: D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin; D007773:Lactates; D019344:Lactic Acid; D006003:Glycogen; D005934:Glucagon; D000409:Alanine; D005990:Glycerol; D009638:Norepinephrine; D004837:Epinephrine