Gastric digestion modifies absorption of butterfat into lymph chylomicrons in rats

Our objective was to characterize the time course of mesenteric lymph output, lipid composition and size of lymph chylomicrons in rats given gastric infusion of lipid emulsions containing defined fractions of butterfat, palm oil or corn oil. The concentrations of cholesterol, triacylglycerol (TAG) and phospholipid in lymph obtained before lipid infusion were 1.4-2.5-fold greater in rats chronically fed palm oil or solid butterfat compared with corn 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 cholesterol output was 1.3-8.6-fold greater than the amount infused in all groups (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 significantly different among treatments. The fatty acid and TAG profiles of lymph chylomicrons obtained from rats infused with corn or palm oil did not differ significantly from that of the emulsion infused. In contrast, gastric lipolysis of butterfat significantly modified the lipid composition of lymph chylomicrons. We observed progressive disappearance of short- and medium-chain fatty acids in gastric contents and an absence of detectable short-chain fatty acids with concurrent proportionate increases in long-chain fatty acids and large TAG molecules in lymph chylomicrons compared with butterfat emulsions. These studies demonstrate that gastric digestion is an important modifier of lipid absorption.