The Oxidation of Palmitic Acid-1-C14 by Extrahepatic Tissues of the Dog

It is generally agreed that the liver is the principal site for the oxidation of higher fatty acids.The question as to whether extrahepatic tissues can oxidize higher fatty acids directly has been long debated.In 1942, Gemmill (1) pointed out that there was no experimental evidence to indicate the direct utilization of fat by mammalian muscle, but this view was not shared by Stadie (2) when he reviewed the subject in 1945.It remained for Lehninger (3), however, to provide the first in vitro evidence of the direct oxidation of a long chain fatty acid by an extrahepatic tissue.This investigator demonstrated that a rat heart muscle suspension can oxidize octanoate, laurate, and palmitate.Kidney and skeletal muscle preparations also gave indications of ability to oxidize higher fatty acids (3).Grafflin and Green have shown that kidney enzyme preparations oxidize rapidly all of the saturated, straight chain, monocarboxylic fatty acids from acetic through n-tridecanoic, with the exception of propionic acid.Myristic, palmitic, stearic, and oleic acids were not oxidized by the kidney system (4).Oxidation of octanoate and trilaurin by various extrahepatic tissue slices has been confirmed by Geyer et al. ( 5).The in viva significance of these findings has not, as yet, been assessed.Nor has indisputable proof that oxidation of naturally occurring fats takes place in the extrahepatic tissues of the intact animal been provided.In the present investigation, we undertook a study of the extent to which the extrahepatic tissues of the intact animal participate in the oxidation of a physiologically occurring fatty acid.Palmitic acid labeled with Cl4 at the carboxyl position was used, and its conversion to Cl402 compared in normal and hepatectomized dogs.