第17期：中鏈脂肪酸在日糧甘油三酯中的位置分布對大鼠淋巴脂質轉運和乳糜微粒組成...

畜牧人小李

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)

翻譯：腸動力研究院 梁琦

摘要

　　本研究通過胸導管插管評估日糧合成脂肪的中鏈脂肪酸（MCF）位置分布是否會影響大鼠膳食脂肪的淋巴轉運和乳糜微粒的化學組成。本次實驗準備了四種類型的合成甘油酯: (i) sn-1(3) MCF-sn 2亞油酸，(ii)酯化sn-1(3) MCF-sn 2亞油酸，(iii)sn-2 MCF-sn-1(3)亞油酸，(iv) 酯化sn-2 MCF-sn-1(3)亞油酸。通過淋巴管插管，由等量的合成脂肪和可可脂組成的純化日糧強飼大鼠。研究結果顯示：膳食脂肪中MCF的位置分布對淋巴回流，甘油三酯、磷脂的生成，乳糜微粒的脂質組成，或微粒大小均沒有顯著影響。合成脂肪中的MCF的位置分布在乳糜脂肪中仍然存在。以上結果表明：在膳食脂肪中的MCF被轉運到了淋巴管并且其位置分布乳糜脂肪中同樣存在。

前言

　　在進行外科手術并且發生胰腺功能不全情況下，中鏈脂肪酸（MCF）的代表：辛酸和癸酸被認為在此情況下能夠及時滿足機體對能量需求的物質。與長鏈脂肪酸相比，因為MCF具有相對較高的極性和易于β-氧化，MCF通過胃腸道時容易被腸系膜靜脈吸收。MCF以甘油三酯的形式在哺乳動物乳汁和椰子油中的含量相對較高。含有MCF的合成脂肪現在被廣泛用于各種領域以提高MCF的生理功能。MCF的吸收似乎比長鏈脂肪酸更好，但是很少有人會關注MCF在長鏈脂肪酸與人造脂肪和膳食脂肪在吸收方面的相互作用。長鏈飽和脂肪酸在甘油三酯分子中的位置極大地影響了相關的腸道吸收率，并因此改變了其他長鏈脂肪酸的吸收速率。我們和其他的研究已經揭示了MCF在脂肪分子中位置的重要性。

　　偶然的一次機會，通過將脂肪乳劑注入胃或十二指腸，發現了大鼠的淋巴系統轉運膳食脂肪。這種方法使數據的解釋更簡單，因為它不需要考慮脂肪乳劑與其他膳食成分的相互作用。相反，這也是該方法的一個缺點，因為膳食組分特別是蛋白質、碳水化合物和磷脂會從口腔到腸道對膳食脂肪的乳化的影響沒有考慮進去。加之，用于此研究的大鼠并不總是從手術相關的壓力中恢復過來的。為了解決這些問題，采用大鼠胸導管插管的方法，但應用這種方法，在膳食脂肪吸收時去分析膳食脂肪的淋巴運輸是不普遍的。

　　在本研究中，飼養的大鼠日糧中添加了特殊結構脂肪含有sn-2或sn-1（3）的MCF及其酯化脂肪。通過淋巴管插管，大鼠吸收體內的這些膳食脂肪時，膳食脂肪的淋巴運輸或淋巴中乳糜微粒的化學組成被檢測出來。

以下是實驗中相關圖表

表1：合成脂肪中總脂肪酸和sn-2脂肪酸

表2：日糧脂肪中總脂肪酸和sn-2脂肪酸     

圖1：大鼠的日糧中添加sn-1(3)中鏈脂肪酸MCF+可可脂（sn-1(3)MCF-S）；酯化sn-1(3)MCF+可可脂（sn-1(3)MCF-I）；sn-2 MCF+可可脂（sn-2 MCF-S）；或酯化sn-2 MCF+可可脂（sn-2 MCF-I），從而計算淋巴流動速率。箭頭表示食物消耗的終止。數值±SEM，n=6.

圖2：大鼠的日糧中添加sn-1(3)中鏈脂肪酸MCF+可可脂（sn-1(3)MCF-S）；酯化sn-1(3)MCF+可可脂（sn-1(3)MCF-I）；sn-2 MCF+可可脂（sn-2 MCF-S）；或酯化sn-2 MCF+可可脂（sn-2 MCF-I）從而計算脂肪，膽固醇，磷脂在淋巴管中的生成速率。箭頭表示食物消耗的終止。數值±SEM，n=6.在兩個小組中，每個時期對應字母的數值顯著不同（P<0.05）。縮寫參見圖1。

表3：大鼠淋巴管乳糜的化學組成和微粒大小

日糧中添加Sn-1（3）MCF或Sn-2MCF類型的合成脂肪

表4：日糧中添加Sn-1（3）MCF或Sn-2MCF類型的合成脂肪飼喂小鼠之后檢測淋巴管乳糜脂肪的脂肪酸組成

啟示

綜上所述，該研究證實了日糧脂肪中的MCF能夠被運輸到淋巴管內，并且其位置分布在乳糜脂肪中也同樣存在。

Abstract

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