Hepatic metabolism of 1‐¹⁴C octanoic and 1‐¹⁴C margaric acids

The hepatic metabolism of 1‐ 14 C margaric acid, a 17 carbon long chain saturated fatty acid which is present in the liver in trace amounts, was compared with 1‐ 14 C octanoic acid and 1‐ 14 C palmitic acid to determine if the enhanced oxidation of medium chain fatty acids to CO 2 was dependent on fatty acid chain length or the endogenous pool size of the fatty acid substrate. Despite the fact that endogenous margarate is present in trace amounts, there was no significant difference in the oxidation of margarate and palmitate to CO 2 , while the oxidation of octanoate to CO 2 was significantly more rapid. Both margarate and palmitate were more readily incorporated into lipid soluble products in contrast to the low rate of incorporation of octanoate. However, margarate was less readily incorporated into triglyceride, phospholipid and monoglyceride than palmitate. These studies suggest that the chain length rather than hepatic content of the fatty acid determines whether the carboxyl group of equimolar amounts of a 1‐ 14 C‐carboxyl labeled fatty acid will be preferentially oxidized to CO 2 or incorporated into tissue lipid in the liver.