Metabolism of Carboxyl-Labeled Short Chain Fatty Acids by the Isolated Dog Heart

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Abstract
A comparative study has been made of the metabolism of short chain carboxyl-labeled fatty acids to CO2 and to glycogen in the isolated dog heart perfused with heparinized blood by the Langendorff technique. In confirmation of previous work by others, at high concentrations of administered acetate-I-C13 this compound contributed from 30–40% of respiratory CO2. Increasing the level of administered acetate correspondingly elevates the contribution of acetate carbon to CO2. The portion of total CO2 derived from 2-, 3-, 4- and 8-carbon fatty acids appeared comparable (5%) at substrate levels of 1–2 mm/l. However, at 12–14 mm/l. the values were 20, 5, 3 and 3% of total CO2 derived from the C13-labeled carboxyl carbon of acetate, propionate, n-butyrate and n-octanoate, respectively. On the assumption of equal rates of combustion of all carbon atoms in each compound, the percentages were 41, 15, 13 and 25%, respectively, of CO2 derived from the administered labeled substrate. Labeled sodium formate was not rapidly converted to respiratory CO2 in a single isolated heart experiment. Carboxyl carbon from none of the labeled fatty acids contributed detectably to carbon of cardiac glycogen.