Free fatty acids as a determinant of myocardial oxygen consumption: a caveat

The present study was designed to determine whether the antilipolytic agent β-pyridylcarbinol modifies left ventricular blood flow distribution. It has been shown that the administration of this agent during isoproterenol infusion reduced both myocardial oxygen consumption and myocardial free fatty acid uptake. Although attributed to a decrease in myocardial free fatty acid uptake, the reduction in myocardial oxygen consumption might also be due to a modification in left ventricular blood flow distribution induced by β-pydidyiearbinol. To verify this possibility left ventricular blood flow distribution was measured with radioactive microspheres in 10 anesthetized dogs during control, during an infusion of isoproterenol (0.2 μg∙kg−1∙min−1) alone, and during an isoproterenol plus β-pyridylcarbinol infusion (0.1 mg∙kg−1∙min−1). In comparison with the control observations, isoproterenol infusion induced a significant increase of 37% in heart rate and of nearly 100% in myocardial free fatty acid uptake, myocardial oxygen consumption, and coronary blood flow, but did not affect the left ventricular blood flow distribution. The addition of β-pyridylcarbinol to the isoproterenol infusion did not cause any significant changes in left ventricular blood flow distribution, although it reduced myocardial free fatty acid uptake by 67% (p < 0.01). Despite this reduction, myocardial oxygen consumption did not change. However, in dogs with a myocardial oxygen uptake above 12.5 mL∙min−1∙100 g−1 during isoproterenol infusion, there was a reduction in myocardial oxygen consumption when β-pyridylcarbinol was added, without significant change in left ventricular blood flow distribution. The present findings reveal that β-pyridylcarbinol does not modify left ventricular blood flow distribution and that the determinant role of free fatty acids on myocardial oxygen consumption is restricted to conditions with increased myocardial demand.