The effect of free fatty acids on oxygen consumption in man: the free fatty acid hypothesis

Abstract

The effect on total body O₂ consumption of induced changes in plasma free fatty acids (FFA) was studied in sixteen healthy men. In the first group (n = 5) plasma FFA was augmented by intravenous infusion of a triglyceride emulsion and heparin, increasing FFA from 0.522±0.11 to 3.025±0.357 mmol/l without any change in total O₂ consumption or in the respiratory quotient. A similar supply of triglyceride emulsion and heparin was given to the second group (n = 6) during continuous infusion of isoproterenol. Isoproterenol alone increased FFA and O₂ consumption. However, O₂ consumption was further increased by an average of 21.1 ml/min˙m² (P<0.005) during exogenous supply of FFA, augmenting plasma FFA from 0.753 ±0.093 to 2.195 ±0.309 mmol/l. The respiratory quotient decreased from 0.85 ±0.04 to 0.79 ±0.04 (P<0.05). In the third group (n = 5) the effect of isoproterenol on O₂ consumption was studied before and after inhibition of lipolysis with β-pyridylcarbinol—a nicotinic acid derivative. During continuous isoproterenol infusion β-pyridylcarbinol reduced plasma FFA from 1.432±0.225 to 0.678 ±0.117 mmol/l and concomitantly O₂ consumption fell by 17.3 ml/min˙m² (P<0.05). Accordingly, elevation of plasma FFA alone had no calorigenic effect on O₂ uptake in the resting non stimulated condition. A rise in plasma FFA caused by catecholamine stimulation is associated with marked calorigenic effect of FFA, suggesting that activation of cyclic AMP may facilitate a waste oxidation of FFA by the mitochondria or recycling of FFA between the FFA and triglyceride pools.

Key Words:

• isoproterenol
• man
• oxygen consumption
• β-pyridylcarbinol
• triglycerides