Docosahexaenoic acid [22:6w3;7,10,13,16,19)] is the major polyunsaturated fatty acid in the photoreceptor membranes of the retina and in cerebral gray matter. It must be obtained either from the diet or by synthesis from other w3 fatty acids, chiefly a-linolenic acid (18:3w3). We tested the effect of dietary w3 fatty acid deprivation during gestation and postnatal development upon the fatty acid composition of the retina and cerebral cortex and upon visual function. Rhesus monkeys (Macaca mulatta) were fed semipurifled diets very low in 18:3w3 throughout pregnancy, and their infants received a similar diet from birth. A control group of females and their infants received a semipurified diet supplying ample 18:3cw.3. In near-term fetuses and newborn infants of the deficient group, the 22:6w3 content of phosphatidylethanolamine was one-half of control values in the retina and one-fourth in cerebral cortex. By 22 months of age, the content of 22:6w3 in these tissues approximately doubled in control monkeys, but it failed to increase in the deficient group. Low levels of 22:6w3 in the deficient animals' tissues were accompanied by a compensatory increase in longer-chain w6 fatty acids, particularly 22:5w6. Functionally, the deficient animals had subnormal visual acuity at 4-12 weeks of age and prolonged recovery time of the dark-adapted electroretinogram after a saturating flash. Abnormally low levels of 22:6&3 may produce alterations in the biophysical properties of photoreceptor and neural membranes that may underlie these functional impairments. The results of this study suggest that dietary w3 fatty acids are essential for normal prenatal and postnatal development of the retina and brain.Neither linoleic acid (18:2w6)t nor a-linolenic acid (18:3w3)
As bstract. Linolenic acid (18:3w3) is a dietary precursor of docosahexaenoic acid (22:6w3), the major fatty acid in the photoreceptor membranes of the retina. We hypothesized that rhesus monkeys deprived of dietary w-3 fatty acids during prenatal and postnatal development would show plasma depletion of these fatty acids and visual impairment. Semipurified diets low in w-3 fatty acids were fed to one group of adult female rhesus monkeys throughout pregnancy and to their infants from birth. A control group of mothers and infants received similar diets but supplying ample linolenic acid. In the plasma phospholipids ofdeficient infants, linolenic acid was generally undetectable and 22:6w3 levels became progressively depleted, falling from 42% of control values at birth to 21% at 4 wk. 9% at 8 wk, and 6% at 12 wk of age. In the other plasma lipid classes, 22:6w3 was undetectable by 12 wk. The visual acuity of the deprived infants, as measured by the preferential looking method, was reduced by one-fourth at 4 wk (P < 0.05) and by one-half at 8 and 12 wk (P < 0.0005) compared with control infants. These results suggest that w-3 fatty acids may be an essential nutrient, and that 22:6w3 may have a specific function in the photoreceptor membranes of the retina.A preliminary report of this work was presented at
Five normolipemic subjects received three test meals containing 28 g n-3 (omega-3) fatty acids provided as 1) triglycerides, 2) ethyl esters, and 3) ethyl esters + 12 g olive oil. The control meal contained olive oil. When equivalent amounts of fat were given, the increase in chylomicron and plasma triglycerides was similar; n-3 fatty acid contents were also similar after n-3 fatty acid intake as ethyl esters or triglycerides. Ethyl esters alone were well absorbed and produced similar n-3 fatty acid responses in plasma triglycerides and chylomicrons. At 24 h after the n-3 fatty acid-containing meals, the fatty acid plasma concentration of these acids was similar. This study showed that n-3 fatty acids in fish oil given as ethyl esters or triglycerides were equally well absorbed. Eicosapentaenoic and docosahexaenoic acids were also equally absorbed.
The consumption of n-3 fatty acids from seafood has been related to a lower incidence of coronary artery disease. Adipose tissue composition has served as a biological marker of chronic ingestion of many dietary polyunsaturated fatty acids. However, the incorporation of n-3 fatty acids into the fat depots has not been studied in humans. Daily dietary supplementation with > or = 10 g n-3 fatty acids from fish oil for > 12 mo resulted in significantly greater 20:5n-3, 22:5n-3, and 22:6n-3 concentrations in fatty acids of adipose tissue, and a greater 20: 5n-3 fatty acid content in plasma lipid classes (cholesterol esters, phospholipids, and free fatty acids) of supplemented subjects compared with nonsupplemented control subjects. Combined values for all subjects indicated that fatty acid concentrations of n-3 plasma lipid classes, including 20:5n-3, 22:5n-3, 22:6n-3, and total n-3, significantly correlated with corresponding concentrations of fatty acids in adipose tissue. These findings indicate that the long-term ingestion of large amounts of n-3 fatty acids in humans resulted in their incorporation into the adipose tissue fatty acids. Incorporation of the fatty acids into adipose tissue warrants consideration for use in clinical studies requiring precise documentation of long-term n-3 fatty acid consumption.
The purpose of this study was t o characterize the lipid classes in hepatic and adipose tissues from cats with idiopathic hepatic lipidosis (IHL). Concentrations of triglyceride, phospholipid phosphorus, and free and total cholesterol were determined in lipid extracts of liver homogenates from 5 cats with IHL and 5 healthy control cats. Total fatty acid composition of liver and adipose tissue was also compared. Triylyceride accounted for 34% of liver by weight in cats with IHL (338 t 38 mg/g wet liver) versus 1% in control cats (9.9 t 1.0 mglg wet liver, P < .001). The mass of cholesterol ester was significantly higher in triglyceride-free (TG-free) liver from cats with IHL (741 t 340 pg/g TG-free wet liver) compared t o healthy cats (31 2 11 p g / g TG-free wet liver, P < ,051. Total fatty acid composition of hepatic tissue in the 2 groups differed; palmitate was higher (19.5 t 1.1% of total fatty acids in cats with IHL versus 9.2 t 2.7% in controls, P < ,051. stearate was lower (8.5 t 0.8% versus 16.8 2 1.1%. P < ,051. oleate was higher (41.2 t 1.6% versus 31.1 2 1.8%.Hepatic lipidosis is a disorder of cats characterized by severe accumulation of fat in the liver, which may result in liver dysfunction and death. It is the most common hepatobiliary disorder of adult cats and the most common cause of liver disease in cats with jaundice.',* Frequently an underlying reason for fat accumulation in hepatocytes is not found, prompting the designation of idiopathic hepatic lipidosis (IHL). It is likely that IHL has multiple causes; speculation has centered on obesity and abnormalities in lipoprotein metabolism, protein-calorie malnutrition, arginine deficiency, damage to hepatic mitochondria, and bacterial toxins. The disease has been associated with a high mortality rate that approaches 100% in cats not supported with aggressive nutritional therapy.3Much has been written, from individual case reports to large retrospective studies, about historical, physical examination, and clinicopathologic features as well as diagnosis and treatment of cats with this syndrome."" Mechanisms for hepatic lipid accumulation have also been proposed, based on current concepts of pathophysiology and on experimental attempts to create hepatic lipidosis in normal ~ats.'.'~-'~ To our knowledge, however, there have been no biochemical studies to evaluate the lipids present in the liver of cats with IHL. The purpose of this study was to characterize the lipids in the liver and adipose tissue in cats with IHL. Materials and Methods Control CatsFive young-adult cats (1 male and 4 nonpregnant females) that were determined to be healthy based on physical examination were studied. These cats were scheduled for use in a subsequent student teaching laboratory. Body weights ranged from 2.8 to 4.5 kg. Although body condition scores were not assigned, none of these cats were obese. The cats were vaccinated against feline panleukopenia, calicivirus infection, and rhinotracheitis and were housed individually in indoor cages. The cats were fed a balanced,...
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