ffect of Medium-Chain Fatty Acid Positional Distribution in Dietary Triacylglycerol on Lymphatic Lipid Transport and Chylomicron Composition in Rats
作者：Octavio CarvajalaMasahiro NakayamaaTaiji Kishi Masao Satoa
Ikuo IkedaaMichihiro Suganob, and Katsumi Imaizumi Laboratory of Nutrition Chemistry, Division of Bioresource and Bioenvironmental Sciences, Graduate School Kyushu University, Fukuoka 812-8581, Japan, and Kumamoto Prefecture University,Kumamoto,Japan
來源：Paper no. L8397 in Lipids 35, 1345–1351 (December 2000)
The present study was carried out to examine ifthe positional distribution of medium-chain fatty acid (MCF) indietary synthetic fat influences lymphatic transport of dietary fat and the chemical composition of chylomicrons in rats with permanent cannulation of thoracic duct. Four types of synthetic triacylglycerol were prepared: (i) sn-1(3)MCF-sn2 linoleic acid, (ii) interesterified sn-1(3)MCF-sn2 linoleic acid, (iii)sn-2MCF-sn-1(3)linoleic acid, and (iv)interesterified sn-2 MCF-sn-1(3) linoleic acid. A purified diet composed of equal amounts of the synthetic fat and cocoa butter was given to rats with permanent lymph duct cannulation. The positional distribution of MCF in the dietary fat had no significant effect on the lymph flow, triacylglycerol output, phospholipid output, lipid composition of chylomicrons, or the particle size. The positional distribution of MCF in the synthetic triacylglycerol was maintained in the chylomicron triacylglycerol. These results showed that MCF in the dietary triacylglycerol is transported into lymphatics and the positional distribution is well preserved in chylomicron triacylglycerol.
Octanoic and decanoic acids are representative medium-chain fatty acids (MCF) that meet a prompt demand for energy under conditions where surgical operations are carried out and pancreatic insufficiency occurs (1,2). MCF, compared with longer-chain fatty acids, are readily absorbed through the stomach as well as intestine via the portal route, as they have a relatively high polarity and susceptibility to β-oxida- tion (1,2). MCF are included to a relatively greater extent in mammalian milk and coconut oils as a form of triacylglyc- erol. Synthetic fats containing MCF are now used in various fields to improve the physiological properties of MCF (3–11). Absorption of MCF seems to be better than longer-chain fatty acids, but little attention has been directed to the interactive effects of MCF on longer-chain fatty acids with regard to ab- sorption of synthetic fats and dietary fats (6,7,12). The position of longer-chain saturated fatty acids in a triacylglycerol molecule greatly influences related intestinal absorption and consequently modifies absorption rates of other longer-chain fatty acids (13–19). The importance of the position of MCF in a triacylglycerol molecule has also been advocated by us (5) and others (6,7,9–12,20,21).
Occasionally, lymphatic transport of dietary fats in rats has been measured by infusing fat-emulsion into the stomach or duodenum (22). This method has an advantage of making the interpretation of data easy since it does not need to take the in- teraction of lipid emulsion with other dietary components into account. Conversely, this is a drawback of this method, since the interaction of dietary components, particularly proteins, carbohydrates, and phospholipids, which influence emulsifi- cation of dietary fats from the mouth to intestine, are not taken into consideration (23). In addition, rats used for this purpose do not always recover from surgery-related stress (24). To ad- dress these problems, permanent cannulation of the thoracic duct has been done in rats (24,25), but application of this method, to characterize the lymphatic transport of dietary lipids during active dietary fat absorption, is not widespread.
In the present studies, rats were kept on diets supplemented with structure-specific fats containing MCF either in sn-2 or sn-1(3) and their interesterified fats. The lymphatic transport of dietary fats or chemical composition of lymph chylomi- crons during active absorption of these dietary fats was deter- mined in rats with a permanent lymph duct cannulation.
Lmplications
In summary, our studies confirmed that MCF in the dietary triacylglycerols are transported into lymphatics and the positional distribution is well preserved in chylomicron triacylglycerol