Cardiac Metabolites: The Importance of Supply and Demand

Abstract

Changes in the mechanical performance of the heart, e.g. an alteration of heart rate or myocardial contractility, affect the myocardial oxygen consumption. Concurrent with these changes in mechanical performance will be changes in the fuel required to maintain energy supplies. If the metabolic rate is increased, then there will be an increased utilisation of substrates to meet the metabolic demand and the reverse if there is a decrease. To produce the ATP required for contraction, the myocardium must extract its substrate from a source, which will be external under normal conditions. The process of substrate “extraction” is the disappearance of a substance from arterial blood into the myocardium. Substrate “oxidation” is the conversion of that substrate to carbon dioxide and water. These two processes may not necessarily be the same if some of the substrate, once in the myocardial cell is utilized by being diverted into other pathways, e.g. synthesis of glycogen or triglyceride.