Microsomal desaturation-elongation of linoleic acid following parenteral feeding with lipid emulsions in the rat

Altered cardiac fatty acid composition and utilization following dexamethasone-induced insulin resistance

Glucocorticoid therapy is often associated with impaired insulin sensitivity and cardiovascular disease. The present study was designed to evaluate cardiac fatty acid (FA) composition and metabolism following acute dexamethasone (Dex) treatment. Using the euglycemic hyperinsulinemic clamp, rats injected with Dex demonstrated a reduced glucose infusion rate. This whole body insulin resistance was also associated with a heart-specific increase in pyruvate dehydrogenase kinase 4 gene expression and a reduction in the rate of glucose oxidation. Dex treatment increased basal and postheparin plasma lipolytic activity. In the heart, palmitic and oleic acid levels were higher after 4 h of Dex and decreased to control (CON) levels within 8 h. Measurement of polyunsaturated FAs demonstrated a drop in linoleic and gamma-linolenic acid, with an increase in arachidonic acid (AA) after acute Dex injection. Tissue FA can be either oxidized or stored as triglyceride (TG). At 4 h, Dex augmented cardiac TG accumulation. However, this increase in tissue TG could not be maintained, such that at 8 h following Dex, TG declined to CON levels. AMP-activated protein kinase (AMPK) activation is known to promote FA oxidation through its control of acetyl-CoA carboxylase (ACC). Acute Dex promoted ACC phosphorylation, and increased cardiac palmitate oxidation, likely through its effects in increasing AMPK phosphorylation and total AMPK protein and gene expression. Whether these acute effects of Dex on FA oxidation, TG storage, and arachidonic acid accumulation can be translated into increased cardiovascular risk following chronic therapy has yet to be determined.

Chain separation of monounsaturated fatty acid methyl esters by argentation thin-layer chromatography

A technique for separating methyl esters of monounsaturated fatty acids by argentation chromatography using silver nitrate-impregnated TLC plates is described. Monounsaturated fatty acid methyl esters are separated from polyunsaturated and saturated fatty acid methyl esters and the monounsaturated fatty methyl esters are resolved according to chain length. cis isomers are well resolved from the corresponding trans isomers. R(F) values for individual monounsaturated fatty acids are very reproducible. The potential of the technique in metabolic studies is demonstrated in the chain elongation of [14C]-18:1(n-9) and delta-9 desaturation of [14C]-18:0 by human skin fibroblasts. Recoveries of individual [14C]-fatty acids for scintillation counting exceed 94%.

Addition of triglycerides with arachidonic acid or docosahexaenoic acid to infant formula has tissue- and lipid class-specific effects on fatty acids and hepatic desaturase activities in formula-fed piglets

The effects of including triglycerides with arachidonic [20:4(n-6)] or docosahexaenoic acid [22:6(n-3)] in formula on plasma chylomicron, LDL and HDL, liver, heart, kidney and brain (n-6) and (n-3) fatty acids were investigated in formula-fed piglets. Piglets were fed formula with (in % total fatty acids) 20% 18:2(n-6) and 2% 18:3(n-3) without or with 0.8% 20:4(n-6) or 0.3% 22:6(n-3) from birth to 18 d. The effects of adding 20:4(n-6) or 22:6(n-3) to the formula differed among different tissues and lipids, with the brain showing resistance to change. Piglets fed formula with 20:4(n-6) had significantly higher plasma, heart and kidney phospholipid and triglyceride, and liver triglyceride 20:4(n-6), but lower plasma and tissue phospholipid 18:2(n-6) than piglets fed formula without 20:4(n-6). Supplementation with 22:6(n-3), in contrast, had no effect on plasma or tissue 18:2(n-6). Higher 22:6(n-3) in liver phospholipid (30-92% greater) and triglyceride (200% greater) in piglets fed formula with 22:6(n-3) rather than without 22:6(n-3) was accompanied by lower 20:4(n-6) in liver phosphatidylethanolamine (mean +/- SEM, 8.6 +/- 0.4 and 10.5 +/- 0.4% fatty acids, respectively), but higher 20:4(n-6) in triglyceride (5.2 +/- 0.4 and 11.5 +/- 0.5%, respectively), and higher liver, heart and kidney phospholipid 20:5(n-3). These results indicate competitive interaction between dietary 20:4(n-6) and tissue 18:2(n-6), and between dietary 20:4(n-6) and tissue 20:5(n-3), rather than 22:6(n-3). The results also show that even at low intakes, dietary 22:6(n-3) or 20:4(n-6) supplementation alters the tissue phospholipid 20:4(n-6) to 20:5(n-3) balance. Studies on the physiologic effects of dietary 20:4(n-6) and 22:6(n-3) supplementation should consider the different sensitivity among tissues to dietary fatty acids.

n-3 fatty acid requirements of the newborn

Whether docosahexaenoic acid (22:6n-3) is an essential nutrient for term or preterm infants, or if not, the quantity of dietary linolenic acid (18:3n-3) needed to support sufficient synthesis of 22:6n-3 for assimilation in the central nervous system is unknown. Infants fed formulas have lower plasma and red blood cell (RBC) levels of 22:6n-3 than breast fed infants. No relationship between the intake of 18:3n-3 in formula (0.8 or 4.5% of fatty acids, 18:2n-6/18:3n-3 ratio 35:1 or 7:1, respectively) and the infant's RBC 22:6n-3 was found. Premature infants (< 33 wk gestation) also showed a decrease in RBC 22:6n-3 during feeding with formula containing 18:3n-3 as the only n-3 fatty acid. However, a marked decrease in plasma and RBC 22:6n-3 occurred between premature birth and the start of full enteral feeding at 1-2 wk of age. This was not reversed by breast milk or formula feeding. Piglets, which are appropriate for studies of infant lipid metabolism, had decreased brain synaptic plasma membrane, retina and liver 22:6n-3 and increased 22:5n-6 when fed formula with 0.8% fatty acids (0.3% of kcal) as 18:3n-3. Formula with 4.0% fatty acids (1.7% of kcal) as 18:3n-3 resulted in similar accretion of 22:6n-3 in the organs compared to milk fed animals. The studies suggest the dietary requirement for 18:3n-3 in term animals in energy balance exceeds 0.3% diet kcal.(ABSTRACT TRUNCATED AT 250 WORDS)

Increments of dietary linoleate raise liver arachidonate, but markedly reduce heart n-6 and n-3 fatty acids in the rat

Four diets containing 20% of energy (en%) as fat and with linoleic acid contents of 1.9, 3.1, 7.7 and 10.1 en%, respectively, were fed to one-month-old male rats for three months. The fatty acid profiles and the levels of the major n-6 and n-3 fatty acids in the lipids of plasma, liver, heart and kidney were measured. We found that with increasing concentrations of 18:2n-6 in the diet, linoleic acid rose in plasma and in all organs, but long-chain n-6 and n-3 fatty acids responded differently. In liver, arachidonic acid increased and n-3 fatty acids were not significantly affected; in heart, both arachidonic and docosahexaenoic acids were progressively reduced; and in kidney, there was no change of n-6 and n-3. The results indicate that incremental changes in dietary linoleate affect the levels of polyunsaturated fatty acids in liver and extrahepatic organs differently.