Effect of fatty acid oxidation on efficiency of energy production in rat heart.

Myocardial fatty acid oxidation has been reported to be accompanied by an elevated O2 consumption compared with carbohydrate oxidation. The exact amount of this additional O2 consumption is controversial. Different investigators have observed an O2 wasting effect that is too large to be explained by the different ATP-to-O2 ratios of these substrates. With the use of isolated perfused rat hearts, O2 consumption and hemodynamic measurements were computer analyzed to provide on-line estimates of the ratio between O2 consumption and demand (EQ). Increasing palmitate or octanoate concentrations decreased the respiratory quotient, which was accompanied by a disproportionate increase of EQ. Inhibition of fatty acid oxidation by an inhibitor of acylcarnitine transferase or a blockade of mitochondrial thiolase caused a drastic reduction of fatty acid oxidation. The fatty acid-induced enhancement of O2 consumption was decreased to a much smaller extent, indicating that there are two different mechanisms responsible for the O2-wasting effect, one that depends on mitochondrial fatty acid oxidation and another that is not affected by an inhibition of this pathway.