Phospholipid and triglyceride metabolism of excised rat diaphragm and the role of these lipids in fatty acid uptake and oxidation

After a 48-hour fast, the phospholipid fatty acids of rat diaphragm are reduced much more than the triglyceride fatty acids. Phospholipid thus appears to contribute more to the labile fatty acids than triglyceride. Both long- and short-chain C14-labeled fatty acids are incorporated into triglyceride but only the long-chain fatty acids are incorporated into phospholipid. After incubation with palmitate-1-C14 and transfer to substrate-free Ringer phosphate, triglyceride specific activity decreases but phospholipid specific activity increases. During incubation with palmitate-1-C14 the triglyceride specific activity rises, then remains constant. Phospholipid specific activity is initially the same as triglyceride but rises at a nearly linear rate. There is net synthesis of triglyceride but not of phospholipid. Combustion of long-chain fatty acids to CO2 indicates the existence of an endogenous dilution pool. It is proposed that phospholipids and triglycerides participate in the oxidation of saturated fatty acids.