Y- Linolenic

Fig. 2. (a) The basis for prostaglandin nomenclature, where the letters A—F and J define principal families (b) defines the side chains for PG derived from dihomo-y-linolenic acid (c) PG2 derived from arachidonic acid and (d), PG derived from eicosapentaenoic acid. 

Some fatty acids are not synthesized by mammals and yet are necessary for normal growth and life. These essential fatty aeids include llnoleic and y-linolenic acids. These must be obtained by mammals in their diet (specifically from plant sources). Arachidonic acid, which is not found in plants, can only be synthesized by mammals from linoleic acid. At least one function of the essential fatty acids is to serve as a precursor for the synthesis of eicosanoids, such as... 

Diethylenetriaminepentaacetic acid DFMO al-Difluoromethyl ornithine DFP Diisopropyl fluorophosphate DFX Desferrioxamine DGLA Dihomo-y-linolenic acid DH Delayed hypersensitivity DHA Docosahexaenoic acid DHBA Dihydroxybenzoic acid DHR Delayed hypersensitivity reaction... 

Free soybean lipoxygenase 9-Hydroperoxy-acid from y-linolenic acid Hexane-borate buffer pH 6.5(1/1) High production only in presence of anionic surfactants 23... 

Cl, critical illness HS, high stress PD, pulmonary disease TR, trauma EPA, eicosapentenoic acid CLA, y-linolenic acid MCT, medium chain triglycerides... 

One formula, Oxepa , has been studied specifically in critically ill patients with acute respiratory distress syndrome (ARDS).29 This high-fat formula contains high quantities of the C0-3 fatty acids (EPA) and y-linolenic acid (GLA). y-Linolenic... 

Dietary polyunsaturated fatty acids (PUFAs), especially the n-3 series that are found in marine fish oils, modulate a variety of normal and disease processes, and consequently affect human health. PUFAs are classified based on the position of double bonds in their lipid structure and include the n-3 and n-6 series. Dietary n-3 PUFAs include a-linolenic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) whereas the most common n-6 PUFAs are linoleic acid, y-linolenic acid, and arachidonic acid (AA). AA is the primary precursor of eicosanoids, which includes the prostaglandins, leukotrienes, and thromboxanes. Collectively, these AA-derived mediators can exert profound effects on immune and inflammatory processes. Mammals can neither synthesize n-3 and n-6 PUFAs nor convert one variety to the other as they do not possess the appropriate enzymes. PUFAs are required for membrane formation and function... 

Octadecatrienoic y-Linolenic 08 3 (n = 6) Major in some seed oils, minor in animals... 

Eicosatrienoic Homo-y- linolenic C20 3 (n = 6) Present in fish oils... 

Linoleic (A 2 octadecadienoic) acid Dihomo-y-linolenic (A8.ii.i4-eicosatrienoic) acid... 

Although these are termed essential fatty acids, they are, in fact, precursors for the major polyunsaturated fatty acids that have essential roles in the body but are present only in small amounts in the diet. Linoleic acid is converted, via elongation and desaturation reactions, to dihomo-y-linolenic (20 3n-6) and then to arachidonic (20 4n-6) acid. a-Linolenic is converted to eicosapentaenoic (20 5n-3) and then docosahexae-noic (22 6n-3). The pathways for formation of these latter fatty acids, from their dietary precursors, are presented in Figures 11.11 and 11.12. Full details of one pathway are provided, as an example, in Appendix 11.4. For comparison of the two pathways, they are presented side by side in Figure 11.13. 

The question arises whether inhibition of the desaturase for this particular pathway can be overcome. The answer is yes. The product of the A desaturase when desaturating linoleic acid is y-linolenic acid. Supplementation of the diet with y-linolenic acid, which bypasses the A desaturase reaction, has been used to increase the formation of dihomo-y-linolenic acid and arachidonic acid (Figure... 

There are several sources of y-linolenic acid including evening primrose, borage and blackcurrant oils. Indeed, the evening primrose is grown commercially for the production of y-linolenic acid. It is available in most health food shops and pharmacies. 

Figure 11.17 Supplementation of diet with y-linolenic acid to overcome a deficiency of A desaturase Supplementation of a diet with DOPA to overcome a deficiency of monooxygenase in Parkinson s disease. A desaturase is a rate-limiting enzyme in the synthesis of arachidonic acid. Supplementation of diet with y-linolenic acid bypasses this enzyme. Damage to neurones in the brain that use dopamine as a neurotransmitter causes a deficiency of rate-limiting a supplement - enzyme, tyrosine monooxygenase, which is bypassed by a supplement, DOPA (dihydroxyphenylalanine). DOPA (usually, described as L-DOPA) is considered by the medical profession as a drug but, in reality, it is a dietary supplement.

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