Gastric digestion modifies absorption of butterfat into lymph chylomicronsin rats

Our objective was to characterize the time course of mesenteric lymph outpu t, lipid composition and size of lymph chylomicrons in rats given gastric i nfusion of lipid emulsions containing defined fractions of butterfat, palm oil or corn oil. The concentrations of cholesterol, triacylglycerol (TAG) a nd phospholipid in lymph obtained before lipid infusion were 1.4-2.5-fold g reater in rats chronically fed palm oil or solid butterfat compared with co rn oil or liquid butterfat (P = 0.02), Total lymph chylomicron TAG output ( mg/24 h) stimulated by gastric lipid infusion was 21% greater with corn oil compared with all saturated fats (P = 0.02). Total lymph chylomicron chole sterol output was 1.3-8.6-fold greater than the amount infused in all group s (P = 0.03) and was independent of the amount of cholesterol infused. The size distribution as well as the mean, median and modal diameters of lymph chylomicrons isolated during peak lymphatic TAG output were not significant ly different among treatments. The fatty acid and TAG profiles of lymph chy lomicrons obtained from rats infused with corn or palm oil did not differ s ignificantly from that of the emulsion infused. In contrast, gastric lipoly sis of butterfat significantly modified the lipid composition of lymph chyl omicrons, We observed progressive disappearance of short- and medium-chain fatty acids in gastric contents and an absence of detectable short-chain fa tty acids with concurrent proportionate increases in long-chain fatty acids and large TAG molecules in lymph chylomicrons compared with butterfat emul sions. These studies demonstrate that gastric digestion is an important mod ifier of lipid absorption.