Fatty acids as energy sources.
نویسنده
چکیده
The notion that fatty acids (FA) can act as a significant source of energy for higher animals has been so much a part of our understanding of metabolism that just to express it seems platitudinous. We can however sharpen the notion a little by suggesting that this is the major function of FA. While protein and carbohydrates can and do act as energy sources they have other quantitatively important functions. The amounts of FA used for other purposes such as membrane synthesis or prostaglandin formation must be quite small relative to their use as an energy source. Moreover, whereas FA when mobilized need not be oxidized, they can be deposited in essentially the same form: the carbon cannot be used for the synthesis of carbohydrate or amino acids whereas these can be converted to FA. Probably most tissues that can carry out aerobic oxidations have at least some capacity to use FA or their products as an energy source. The pregnant uterus appears to be largely carbohydrate-dependent, but it does appear to use small amounts of ketones (A. Domanski, B. P. Setchell & D. B. Lindsay, unpublished results) and this is also true of the foetus itself (Morriss, Boyd, Makowski, Meschia & Battaglia, 1974). The brain was also for many years supposed to use only carbohydrate, but there is evidence that ketones can be utilized in starving man (Owen, Morgan, Kemp, Sullivan, Herrera & Cahill, 1967) and rats (Hawkins, Williamson & Krebs, 1971). The sheep brain does not normally appear to use acetate or ketones (Lindsay & Setchell, 1972, 1974) but we have recently found that when acetoacetate is infused intravenously into sheep so that the concentration in blood is higher than is normally found even in ketotic animals, there does Seem to be a small utilization of acetoacetate. Even if we accept provisionally that most tissues have at least some capacity to use FA or their oxidation products as energy sources, it is clear that the extent to which this occurs varies considerably between tissues; moreover, for many tissues the amount used is likely to depend on the relative availability of substrates and the physiological state of the animal. I propose in this review to discuss how far we can estimate quantitatively the contribution of FA in meeting energy requirements. In principle this should be a fairly straightforward problem since “C-labelled FA have become available.
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عنوان ژورنال:
- The Proceedings of the Nutrition Society
دوره 34 3 شماره
صفحات -
تاریخ انتشار 1975