The Metabolism of Chylomicra. I. The Removal of Palmitic Acid-1-C14 Labeled Chylomicra From Dog Plasma

It is now generally accepted that the intestinal lymphatics constitute the exclusive pathway for the absorption of long chain fatty acids, whether ingested unesterified or as glycerides. These fatty acids appear in the thoracic duct lymph as chylomicra. The subsequent fate of the absorbed fat has been explored very little, and the role of plasma lipoproteins in chylomicron transport and the sites of removal of the absorbed fat remain unknown. Approximately 95 per cent of long chain fatty acids appear in the lymph as triglycerides and 5 per cent as phospholipids (1). Bergstrom, Borgstrom, and Rottenberg (2) fed labeled stearic acid and tristearin to fasting rats. Over a period of 3 to 4 hours, approximately 1 mg. per minute of fatty acids was delivered to and removed from the total plasma, which contained only about 5 mg. of preformed triglycerides. The maximum specific activities of plasma triglyceride fatty acids were only 4 and 15 per cent of the specific activities of the fed stearic acid and tristearin, respectively. The authors suggested that the absorbed triglycerides were not mixing appreciably with the existing plasma triglycerides. Their data did not exclude the possibility that the plasma triglycerides were exchanging rapidly with a large triglyceride pool.