Digestion and absorption of milk triacylglycerols in 14-day-old suckling rats.

The fatty acid compositions of the major classes of lipid recovered from the contents of the stomach and small intestine, as well as, the chylomicron fraction of the serum of 14-day-old rats have been compared to that of the milk triacylglycerols. The results indicate that at least two lipolytic activities are involved. As well as pancreatic lipase in the small intestine, a second lipase is present in the stomach and removes approximately half of the medium-chain acids (8:0, 10:0, 12:0) which together comprise between 30 and 50% of the total milk fatty acids. Tracer amounts of radioactively labeled fatty acids were then fed with carrier milk lipid and the kinetics of the appearance of the label in the blood determined. The very rapid appearance (less than 5 minutes) of 8:0 and 10:0 suggested that these acids are absorbed directly across the stomach wall and transported as the free acid. The longer times required for the other acids fed indicate that they are abosrbed from the small intestine. While both 16:0 and 18:1 were predominantly esterified into triacylglycerols and secreted in the chylomicrons, 12:0 was transported mainly as the free acid via the portal vein. Unlabeled 9:0, 11:0 and 13:0 were each absorbed and transported as the next higher homolog.