Glucose kinetics during prolonged exercise in euglycaemic and hyperglycaemic subjects.
To determine the limits to oxidation of exogenous glucose by skeletal muscle, the effects of euglycaemia (plasma glucose 5 mM, ET) and hyperglycaemia (plasma glucose 10 mM, HT) on fuel substrate kinetics were evaluated in 12 trained subjects cycling at 70% of maximal oxygen uptake (VO2, max) for 2 h. During exercise, subjects ingested water labelled with traces of U-14C-glucose so that the rates of plasma glucose oxidation (Rox) could be determined from plasma 14C-glucose and expired 14CO2 radioactivities, and respiratory gas exchange. Simultaneously, 2-3H-glucose was infused at a constant rate to estimate rates of endogenous glucose turnover (Ra), while unlabelled glucose (25% dextrose) was infused to maintain plasma glucose concentration at either 5 or 10 mM. During ET, endogenous liver glucose Ra (total Ra minus the rate of infusion) declined from 22.4 +/- 4.9 to 6.5 +/- 1.4 mumol/min per kg fat-free mass [FFM] (P < 0.05) and during HT it was completely suppressed. In contrast, Rox increased to 152 +/- 21 and 61 +/- 10 mumol/min per kg FFM at the end of HT and ET respectively (P < 0.05). HT (i.e., plasma glucose 10 mM) and hyperinsulinaemia (24.5 +/- 0.9 microU/ml) also increased total carbohydrate oxidation from 203 +/- 7 (ET) to 310 +/- 3 mumol/min per kg FFM (P < 0.0001) and suppressed fat oxidation from 51 +/- 3 (ET) to 18 +/- 2 mumol/min per kg FFM (P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)
Hawley
J A
JA
Medical Research Council, Observatory, South Africa.
Bosch
A N
AN
Weltan
S M
SM
Dennis
S C
SC
Noakes
T D
TD
D000328:Adult; D001786:Blood Glucose / Q000032:analysis*; D050260:Carbohydrate Metabolism; D015444:Exercise / Q000502:physiology*; D005947:Glucose / Q000032:analysis / Q000378:metabolism / Q000493:pharmacokinetics*; D015309:Glucose Clamp Technique; D006801:Humans; D006943:Hyperglycemia / Q000097:blood / Q000503:physiopathology*; D007262:Infusions, Intravenous; D007328:Insulin / Q000097:blood; D050356:Lipid Metabolism; D008297:Male; D009132:Muscles / Q000378:metabolism; D010084:Oxidation-Reduction; D013997:Time Factors; D014316:Tritium
D001786:Blood Glucose; D007328:Insulin; D014316:Tritium; D005947:Glucose