Effect of soybean oil and soybean lecithin on intestinal lipid composition and lipid droplet accumulation of rainbow trout, Oncorhynchus mykiss Walbaum |
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Authors: | Rolf Erik Olsen Bjørn Tore Dragnes Reidar Myklebust Einar Ringø |
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Institution: | 1. Matre Aquaculture Research Station, Institute of Marine Research, Matredal, Norway 2. Department of Marine Biotechnology, Norwegian College of Fishery Science, University of Troms?, Norway 3. Institute of Anatomy and Cell Biology, University of Bergen, Norway 4. Department of Food Safety and Infection Biology, Norwegian School of Veterinary Science, Troms?, Norway 5. Aquaculture Protein Centre, Norway
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Abstract: | Rainbow trout (Oncorhynchus mykiss Walbaum) were fed purified diets containing fish oil for six weeks and then soybean lecithin or soybean oil for 25 days.
The gastrointestinal tract segments, stomach, midgut and hindgut were then sampled for lipid and fatty acid composition and
electron microscopy. Membrane lipid class composition was fairly similar in all three segments of trout fed fish oil. Hindgut
contained slightly more phosphatidylserine than stomach and midgut, while midgut contained more phosphatidylcholine and less
lysophospatidylcholine/sphingomyelin. Feeding soybean products appeared to marginally decrease free cholesterol. The fatty
acid compositions of the main lipid classes showed significant regional differences. In control fish, stomach had higher levels
of arachidonic acid (20:4n-6) and n-6 polyunsaturated fatty acids than midgut and hindgut, and lower content of docosahexaenoic
acid (22:6n-3) and n-3 polyunsaturated fatty acids. Midgut phosphatidylethanolamine also had higher levels of saturated fatty
acids and less n-3 polyunsaturated fatty acids than the other tissues. Feeding soybean products decreased the n-3/n-6 ratio
mainly due to increases in linoleic (18:2n-6) and 20:4n-6 and decreases in 22:6n-3 and eicosapentaenoic acid (20:5n-3). Phosphatidylcholine
and to a lesser extent phosphatidylethanolamine adapted more readily to dietary changes by major increases in 18:2n-6 and
C20−22 n-6 polyunsaturated fatty acids. The composition of phosphatidyl-serine and -inositol appeared to be under more strict metabolic
control. Linoleic acid hardly increased at all while the increase in other n-6 polyunsaturated fatty acids was less pronounced
than for the other lipid classes. Regardless of lipid class, stomach resisted dietary changes more strongly than midgut and
hindgut. Increases in n-6 polyunsaturated fatty acids were minor as were the loss of n-3 polyunsaturated fatty acids. The
dead-end product 20:2n-6 accumulated to a higher degree in hindgut phosphatidyl-ethanolamine and -coline compared to midgut
and stomach, suggesting that the activity of Δ6 desaturation is higher in the anterior part of the intestine where most of the lipid is absorbed. Feeding soybean oil caused
massive accumulation of free lipid droplets in midgut enterocytes while little lipid droplets were observed in trout fed fish
oil or soybean lecithin. Since both soybean products influenced intestinal composition to the same degree, altered fatty acid
profiles in membranes is not responsible for the observed lipid accumulation. This supports previous observations in Arctic
charr (Salvelinus alpinus L.), suggesting that fish may require exogenous phospholipids in order to sustain a sufficient rate of lipoprotein synthesis.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | Gastrointestinal tract stomach enterocytes histology ultrastructure fatty acid composition lipid class composition |
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