Hepatic Metabolism of Dietary Alpha-Linolenic Acid in Suckling Rats, and Its Possible Importance in Polyunsaturated Fatty Acid Uptake by the Brain

Abstract

The presence of large amounts of long chain-polyunsaturated fatty acids (PUFA) in the brain implies an exogenous intake of unsaturated fatty acids, either as essential fatty acids, or in the form of higher homologues resulting from hepatic metabolism. To determine the influence of the diet upon the potential availability of polyunsaturated fatty acids to the brain, four different diets were used with comparable amounts of 18:2 n-6, but variable amounts of 18:3 n-3 (0.2, 1, 2 and 9%). These diets were administered to female rats from the day of mating and during the periods of gestation and lactation. Fifteen days after birth suckling animals were killed and the fatty acid distribution was studied in the serum in two lipoprotein classes (VLDL-LDL and HDL). On the whole, an increase in dietary 18:3 n-3 resulted in an increase of polyunsaturated fatty acids of the n-3 series and a decrease in fatty acids of the n-6 series. The modification chiefly concerned the terminal fatty acids in each series (22:5 n-6 and 22:6 n-3). It is noteworthy that the influence of exogenous 18:3 n-3 upon the 20:4 n-6 content of lipoproteins was not significant below 2% of 18:3 n-3 intake, a level that we have previously shown to be both necessary and sufficient to satisfy the requirements of the brain for fatty acids of the n-3 series. In the liver, the intermediary metabolism ensures an important release of long-chain polyunsaturated fatty acids, which may help to satisfy the lipid requirements of the brain.

The role of n-3 polyunsaturated fatty acids in brain: Modulation of rat brain gene expression by dietary n-3 fatty acids

“…In addition, both fatty acids brought also some alteration of 18:0͞22:6 diacyl phosphatidylethanolamine subclasses (Table 4), indicating that (i) 18:3n-3 must have been converted to DHA either in liver (12,13) or in astrocytes as suggested by Spector and Moore (37), and (ii) n-3 polyunsaturated fatty acids affect brain lipid metabolism. Although the level of 18:0͞22:6 containing ethanolamine plasmalogen species was identical in all three food regimens, a roughly 20% increase in the level of this subclass in fish oil-fed rat brains indicates that a portion of DHA, in addition to diacyl subclass, was deposited in ethanolamine plasmalogens.…”

“…Indeed, cerebral cortex DHA level is higher in breast-fed infants than in formula-fed ones (11). Most of the brain DHA is supplied by the liver during pregnancy (12,13) and by breast feeding after delivery (11). The exact mode of action of DHA-containing phospholipids on cognitive functions is not known, but there might be a relationship between their effect on blood-brain barrier (14), membrane fluidity (15), activity of some enzymes (8,16), neural signaling (17), ionic channels (18), or control of nerve growth factor (19).…”

Docosahexaenoic Acid Is the Preferred Dietary n-3 Fatty Acid for the Development of the Brain and Retina

“…It has been suggested that the brain receives much of its complement of DHA "preformed" from the circulation via the liver (33,34), although the rat brain, and especially the developing rat brain, has a substantial capacity for the synthesis of DHA from precursor molecules (35,36). Our results showed that DHA was formed from dietary EPA and accumulated in the brain to nearly the same extent as the DHA when fed directly in the diet.…”

Dietary fish oil replacement with lard and soybean oil affects triacylglycerol and phospholipid muscle and liver docosahexaenoic acid content but not in the brain and eyes of surubim juveniles Pseudoplatystoma sp.

“…Small amounts of 22:6n -3 and several of its n -3 PUFA precursors are normally present in the plasma (Lands et al 1992;Conquer and Holub 1998), and there is evidence that the brain can utilize all of these substrates. A number of studies of experimental animals have shown that plasma 22:6n -3, either obtained directly from the diet or synthesized in the liver from n -3 PUFA precursors, is the main source of 22:6n -3 for the brain (Sinclair 1975;Nouvelot et al 1986;Scott and Bazan 1989;Sheaff Greiner et al 1996;Pawlosky et al 1996;Su et al 1999). This is consistent with the observation that fatty acid D6-desaturase, the rate-limiting enzyme in the conversion of n -3 PUFA precursors to 22:6n -3 in vertebrates (Hastings et al 2001), decreases in the brain soon after birth (Bourre et al 1990).…”