Role of plasma non-esterified fatty acids during and after exercise

1. The importance of circulating non-esterified fatty acids as a substrate during and after low-grade exercise has been examined by using a nicotinic acid analogue to inhibit lipolysis. Seven healthy men received acipimox or placebo on separate occasions. After 90 min, bicycle exercise was performed for 45 min (40% of pre-determined maximum oxygen uptake), followed by a 60 min recovery period. 2. The plasma concentration of non-esterified fatty acids increased during exercise after placebo (320 +/- 80 to 630 +/- 110 mumol/l) and remained elevated in the post-exercise period. Basal concentrations were lower after acipimox (100 +/- 10 mumol/l; P less than 0.05); they declined to 60 +/- 10 mumol/l during exercise and remained at this level for the rest of the study. 3. Lipid oxidation increased from 0.8 +/- 0.1 to 4.2 +/- 0.5 mg min-1 kg-1 during exercise after placebo (P less than 0.001) and remained elevated in the post-exercise period (1.2 +/- 0.1 mg min-1 kg-1). It was lower after acipimox, but still increased from 0.3 +/- 0.1 to 2.3 +/- 0.2 mg min-1 kg-1 with exercise. Carbohydrate oxidation was increased after acipimox compared with after placebo, but only reached significance during the post-exercise period (P less than 0.05). 4. Although acipimox abolished the rise in the plasma concentration of non-esterified fatty acids during exercise, there was only a 50% decrease in the rate of lipid oxidation. This suggests that an alternative source of non-esterified fatty acids makes an important contribution to the supply of lipid for oxidation during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)