Effects of increased fat availability on fat-carbohydrate interaction during prolonged exercise in men

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 1998-04, Vol.274 (4), p.894-R902
• Main Authors: Odland, L. Maureen, Heigenhauser, George J. F, Wong, Denis, Hollidge-Horvat, Melanie G, Spriet, Lawrence L
• Format: Article
• Language: English
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.1998.274.4.r894

Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario N1G 2W1; and Department of Medicine, McMaster University, Hamilton, Ontario, Canada L8N 3Z5 The study examined the existence and regulation of fat-carbohydrate interaction during low- and moderate-intensity exercise. Eight males cycled for 10 min at 40% and 60 min at 65% maximal O 2 uptake ( O 2 max ) while infused with either Intralipid and heparin (Int) or saline (Con). Before exercise, plasma arterial free fatty acid (FFA) was 0.69 ± 0.04 mM (Int) vs. 0.25 ± 0.04 mM (Con). Muscle biopsies were taken at rest and at 10, 20, and 70 min of exercise. Arterial and femoral venous blood samples and expired gases were collected simultaneously throughout exercise, and blood flow was estimated from pulmonary O 2 uptake and the leg arterial-venous O 2 difference. Respiratory exchange ratio was higher in Con (0.94 ± 0.01) compared with Int (0.91 ± 0.01). Mean net leg FFA uptake was higher in Int (0.16 ± 0.03 vs. 0.04 ± 0.01 mmol/min), and net lactate efflux was reduced (Int, 1.55 ± 0.36 vs. Con, 3.07 ± 0.47 mmol/min). Leg net glucose uptake was unaffected by Int. Muscle glycogen degradation was 23% lower in Int [230 ± 29 vs. 297 ± 36 mmol glucosyl units/kg dry muscle (dm)]. Pyruvate dehydrogenase activity in the a form (PDH a ) was lower during Int (1.61 ± 0.17 vs. 2.22 ± 0.24 mmol · min 1 · kg wet muscle 1 ), and muscle citrate was higher (0.59 ± 0.04 vs. 0.48 ± 0.04 mmol/kg dm). Muscle lactate, phosphocreatine, ATP, acetyl-CoA, acetyl-carnitine, and P i were unaffected by Int. Calculated free AMP was significantly lower in Int compared with Con at 70 min of exercise (3.3 ± 0.8 vs. 1.5 ± 0.3 µmol/kg dm). The high FFA-induced reduction in glycogenolysis and carbohydrate oxidation at 65% O 2 max appears to be due to regulation at several sites. The reduced flux through phosphorylase and phosphofructokinase during Int may have been due to reduced free AMP accumulation and increased cytoplasmic citrate. The mechanism for reduced PDH transformation to the a form is unknown but suggests reduced flux through PDH. glucose-fatty acid cycle; glycogen phosphorylase; pyruvate dehydrogenase; citrate; acetyl-coenzyme A; free adenosine monophosphate; phosphofructokinase