Abstract
Dietary fats are efficiently absorbed in the small intestine and transported into the blood via the lymph as chylomicrons, despite enormous variations in the amount and composition of the dietary lipid. The aim of the present study was to investigate how enterocytes respond to increased dietary fats of different composition. Rabbits were fed a low fat chow diet, and chow supplemented with sunflower oil (high n-6 polyunsaturated fatty acids), fish oil (high n-3 polyunsaturated fatty acids), or an oil mixture of a composition similar to that of the typical western diet. Feeding fat for 2 weeks markedly stimulated the ability of the isolated enterocytes to synthesize and secrete apolipoprotein B48, triacylglycerol, and cholesteryl ester (up to 18-, 50-, and 80-fold, respectively) in particles of chylomicron density. The magnitude of stimulation was sunflower oil > western diet lipid > fish oil. Single doses of lipid given 18 h prior to isolation of enterocytes stimulated chylomicron secretion by only 10% of that observed after 2 weeks of dietary supplementation. Enterocytes are replaced rapidly (half-life 1-2 days) by cells which move from the crypts to the tips of the villi, where absorption of nutrients takes place. Our observations suggest that dietary lipids modulate the function of enterocytes as they move from the crypts, so that the cells are 'turned-on' to lipid absorption. The results also show that diets of different fatty acid composition vary in their effects.
Highlights
Dietary fats are efficiently absorbed in the small intestine and transported into the blood via the lymph as chylomicrons, despite enormous variations in the amount and composition of the dietary lipid
Synthesis of the radiolabeled lipids reached a peak in the cells after about 30–60 min incubation and secretion followed the same pattern as Apolipoprotein B-48 (apoB-48)
As shown previously [14], secretion was dependent on addition of micelles to the incubation medium and Ͼ90% of the secreted radiolabeled apoB-48 and lipids was recovered in the chylomicron fraction floated from the incubation medium by centrifugation at 13,000 g for 20 min
Summary
Dietary fats are efficiently absorbed in the small intestine and transported into the blood via the lymph as chylomicrons, despite enormous variations in the amount and composition of the dietary lipid. Feeding fat for 2 weeks markedly stimulated the ability of the isolated enterocytes to synthesize and secrete apolipoprotein B48, triacylglycerol, and cholesteryl ester (up to 18-, 50-, and 80-fold, respectively) in particles of chylomicron density. The magnitude of stimulation was sunflower oil Ͼ western diet lipid Ͼ fish oil. Single doses of lipid given 18 h prior to isolation of enterocytes stimulated chylomicron secretion by only 10% of that observed after 2 weeks of dietary supplementation. Our observations suggest that dietary lipids modulate the function of enterocytes as they move from the crypts, so that the cells are ‘turned-on’ to lipid absorption. The results show that diets of different fatty acid composition vary in their effects.—Cartwright, I. Increased dietary triacylglycerol markedly enhances the ability of isolated rabbit enterocytes to secrete chylomicrons: an effect related to dietary fatty acid composition.
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