title: Effect of elevated FFA on carbohydrate and lipid oxidation during prolonged exercise in humans.
abstract: Increased availability of circulating free fatty acids (FFA) inhibits the rate of glycolysis in heart and resting skeletal muscle (Randle effect). Whether elevated FFA may play a role in decreasing carbohydrate oxidation during prolonged exercise in humans is more controversial. Using respiratory exchange measurements, we measured substrate utilization during 2.5 h of exercise at approximately 44 +/- 1% maximal O2 uptake (VO2 max) in the presence or absence of elevated FFA levels. After 30 min of base-line determinations, 1,000 U heparin was given intravenously and a 3-h constant infusion of Intralipid 10% (150 g/h) and heparin (500 U/h) was started. After an additional 30 min of rest, subjects exercised for 2.5 h (study 1, n = 6). In another five subjects (study 2) 100 g glucose was ingested after 30 min of exercise. The same protocols (studies 1 and 2) were also performed during a 0.9%-saline infusion. During exercise, without glucose ingestion, higher FFA concentrations prevailed during the Intralipid infusion (1,122 +/- 40 vs. 782 +/- 65 mumol/l), but the relative contributions of carbohydrate (49 +/- 4 vs. 50 +/- 4%) or lipid (49 +/- 4 vs. 47 +/- 6%) oxidation to the total energy expenditure were different only during the first 30 min of exercise. Similarly, higher FFA levels (1,032 +/- 62 vs. 568 +/- 46 mumol/l) did not alter the relative contributions of carbohydrate (62 +/- 4 vs. 69 +/- 2%) or lipid (36 +/- 4 vs. 29 +/- 2%) oxidation to the total energy expenditure after glucose feeding.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D020155:3-Hydroxybutyric Acid; D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D050260:Carbohydrate Metabolism; D004435:Eating; D005230:Fatty Acids, Nonesterified / Q000097:blood*; D005947:Glucose / Q000494:pharmacology; D005990:Glycerol / Q000097:blood; D006801:Humans; D006885:Hydroxybutyrates / Q000097:blood; D007328:Insulin / Q000097:blood; D007773:Lactates / Q000097:blood; D050356:Lipid Metabolism; D008297:Male; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D005082:Physical Exertion; D011659:Pulmonary Gas Exchange; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D006885:Hydroxybutyrates; D007328:Insulin; D007773:Lactates; D005947:Glucose; D005990:Glycerol; D020155:3-Hydroxybutyric Acid