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

¹ From the Department of Physiology, Medical School, University of Minnesota, Minneapolis, Minnesota

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.