Acid Composition Of Cholesterol Esters Research Articles

Fatty acid composition of cholesterol esters reflects dietary fat intake after dietary interventions in a multinational population

BackgroundThe effects of different dietary fatty acids (FA) on cardiovascular risk still needs clarification. Plasma lipids composition may be a biomarker of FA dietary intake. PurposeTo evaluate in a composite population the relationships between changes in dietary fat intake and changes in FA levels in serum cholesterol esters. MethodsIn a multinational, parallel-design, dietary intervention (KANWU study), dietary intakes (3-day food record) and FA composition of serum cholesterol esters (gas-liquid chromatography) were evaluated at baseline and after 3 months in 162 healthy individuals, randomly assigned to a diet containing a high proportion of saturated (SFA) or monounsaturated (MUFA) fat, with a second random assignment to fish oil or placebo supplements. ResultsMain differences in serum lipid composition after the two diets included saturated (especially myristic, C14:0, and pentadecanoic, C15:0) and monounsaturated (oleic acid, C18:1 n-9) FA. C14:0 and C15:0 were related to SFA intake, while C18:1 n-9 was associated with MUFA intake. Fish oil supplementation induced a marked increase in eicosapentaenoic (C20:5 n-3) and docosahexaenoic (C22:6 n-3) acids. After the 3-month intervention, Δ-9 desaturase activity, calculated as palmitoleic acid/palmitic acid (C16:1/C16:0) ratio, was more reduced after the MUFA (0.31±0.10 vs 0.25±0.09, p<0.0001) than SFA diet (0.31±0.09 vs 0.29±0.08, p=0.006), with a statistically significant difference between the two groups (p<0.0001). ConclusionsThis study shows that serum cholesterol ester FA composition can be used during randomized controlled trials as an objective indicator of adherence to experimental diets based on saturated and monounsaturated fat modifications, as well as fish oil supplementation.

Abnormal content of n−6 and n−3 long-chain unsaturated fatty acids in the phosphoglycerides and cholesterol esters of parahippocampal cortex from Alzheimer's disease patients and its relationship to acetyl CoA content

The long-chain fatty acid composition of cholesterol esters, phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI) from parahippocampal cortex of Alzheimer's disease (AD) patients and control subjects was examined. In general the PC fraction contained less polyunsaturated long-chain fatty acids than did PE, PS or PI. Of the n−6 polyunsaturated long-chain fatty acids, PI contained the greatest incorporation of these acids followed by PE. There were significant differences between controls and AD patients in total n−6 EFAs. Arachidonic acid (C20:4 n−6) was the predominant fatty acid of this family found to be present. In AD, PE and PS showed a deficit of adrenic acid (C22:4 n−6) content and PE also contained less arachidonic acid. In AD subjects, the cholesterol esters contained significantly less n−3 polyunsaturated fatty acids with, specifically, a reduction in alpha-linolenic acid. Acetyl CoA content of hippocampal cortex was greater in AD patients than in control subjects indicating either an increased extent of oxidative metabolism or a failure to utilise acetyl CoA for anabolic processes. Abnormal magnitude of oxidative processes could give rise to the biosynthesis of PE and PS species containing less n−6 polyunsaturated fatty acids than occurs in control subjects.

Solvent Vapor Abuse Leukoencephalopathy. Comparison to Adrenoleukodystrophy

Chronic organic solvent vapor inhalation can cause permanent damage to the central nervous system. Clinical features and radiologic abnormalities are well known, but pathology has not been definitely established. This study describes the gross, microscopic and ultrastructural changes and fatty acid composition of cholesterol esters in the brain of two chronic paint sniffers as well as the electron microscopic findings from a third, all with permanent neurological impairment. The abnormalities which were the same in all cases consisted of a demyelinating process which grossly manifested itself as brain atrophy and subtle discoloration of the cerebral and cerebellar white matter. Periodic acid-Schiff-positive macrophages in the absence of foamy macrophages were the histological hallmark of this process. Electron microscopy revealed oval membrane-bound cytoplasmic bodies filled with bundles of trilaminar inclusions composed of 3 nm paired dense leaflets separated by a space 3-7 nm wide in macrophages. Biochemical analysis showed an increase of very long chain fatty acids in the white matter cholesterol esters. This study defines the morphologic substrate of solvent vapor abuse leukoencephalopathy. The novel ultrastructural observations in conjunction with biochemical findings provide a link with adrenoleukodystrophy and raise the possibility of similar mechanisms of myelin degradation in both.

Compositions of Serum Lipids, Lipoproteins, and Lipoprotein Fatty Acids in Type IV Primary Hypertriglyceridemia.

The overall composition of serum lipoproteins and the fatty acid composition of cholesterol esters and phospholipids in the VLDL, IDL, LDL, and HDL were studied in eleven patients with familial type IV primary hypertriglyceridemia. The patients were divided into two groups: HTG 1 (serum triglycerides below 350mg/dl: 200-294, n=5) and HTG2 (serum triglycerides above 350mg/dl: 368-820, n=6). The data were compared with those from 9 normolipidemic subjects.The proportion of the constituents of VLDL was normal in the HTG1 group, but cholesterol esters were increased and triglycerides decreased in this fraction in the HTG2 one. The increase in triglycerides and decrease in cholesterol esters in LDL and HDL modified the CE/TG and TG/total lipoprotein ratios in both groups of patients. The core lipid/surface ratio was increased in HDL in both groups, but not in the other three fractions.The saturated fatty acids of cholesterol esters were low (p<0.01) in the VLDL of the HTG2 group. The ω6 fatty acids of cholesterol esters and phospholipids were slightly increased (p<0.05) in the VLDL in the same group. However, there was a decrease in the ω6 fatty acids in cholesterol esters (p<0.05) and in the phospholipids (p<0.01) in the IDL of the HTG1 group. There was no significant difference in the LDL fatty acid composition between the hypertriglyceridemic patients and the controls. The phospholipids of the HDL in the HTG2 group contained less (p<0.05) saturated fatty acids and more (p<0.05) polyunsaturated fatty acids than did those in the HTG1 group.These observations suggest that the fatty acid composition of lipoproteins in hypertriglyceridemic subjects is not markedly altered and is not related to the major changes in the lipoprotein composition of their fractions.

Effect of simvastatin and fenofibrate on the fatty acid composition of hypercholesterolaemic patients.

1. The effects of simvastatin (one of a new class of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase inhibitors) and fenofibrate on the fatty acid composition of cholesterol esters, phospholipids and triglycerides of different lipoproteins of 15 patients with primary hypercholesterolaemia were compared in a double-blind study. 2. Fenofibrate (300 mg day-1) increased the relative content of saturated fatty acids of cholesterol esters, phospholipids and triglycerides in VLDL, IDL and HDL. It also increased the relative content of monounsaturated fatty acids of cholesterol esters and phospholipids in all fractions and those of triglycerides in VLDL and IDL. In contrast, it decreased the proportion of polyunsaturated fatty acids of cholesterol esters and phospholipids in all fractions and those of triglycerides in VLDL and IDL. The polyunsaturated/saturated (P/S) ratio was reduced in cholesterol esters and phospholipids in VLDL and in phospholipids in IDL by fenofibrate. The drug significantly increased the 18:1w9/18:2w6 ratio in cholesterol esters and phospholipids in VLDL, LDL and HDL, but produced a non-significant increase in the ratio in IDL. 3. Simvastatin (20 mg day-1) produced a significant decrease in saturated fatty acid and an increase in polyunsaturated fatty acid in triglycerides in VLDL. Simvastatin, in contrast to fenofibrate caused a slight decrease in saturated and monounsaturated fatty acids in the three other lipoprotein fractions, and an increase in polyunsaturated fatty acids. The P/S and 18:1w9/18:2w6 ratios were not modified by simvastatin.

Effect of Dietary Treatment on the Lipid, Lipoprotein and Fatty Acid Compositions in Type IV Familial Hypertriglyceridemia

The effects of a 2-month dietary treatment (1,625 +/- 177 kcal, 40 +/- 2.3% carbohydrate, 35 +/- 3.7% fat, 25 +/- 2% protein, polyunsaturated/saturated fat ratio = 1.02 +/- 0.06) on the overall composition of serum lipids, lipoproteins and the fatty acid composition of cholesterol esters and phospholipids in very low (VLDL), intermediate (IDL), low (LDL) and high (HDL) density lipoprotein in 5 patients with primary familial hypertriglyceridemia type IV were assessed. The data were compared with those for 9 normolipidemic subjects. Treatment decreased serum triglycerides (-52%) and total cholesterol (-12%) due to decrease in free cholesterol (-30%). It produced a significant decrease in all the constituents of VLDL (-58%), but the VLDL remained significantly higher after treatment than those of control subjects. The diet caused a decrease in triglycerides (-16%, -29% and -33%, respectively), and an increase in cholesterol in IDL, LDL and HDL. The IDL level in the treated patients remained significantly higher than in the controls. The LDL cholesterol/HDL cholesterol ratio was unchanged after treatment. The fatty acid compositions of the patients before treatment and the controls were not significantly different. The diet caused a decrease in palmitoleic and oleic acids in the cholesterol ester fraction and an increase in linoleic acid, but this was significant only in VLDL and HDL. The diet decreased the eicosapentaenoic acid but the drop was only significant in IDL and LDL. There was also a decrease in linolenic acid, only significant in IDL. The diet induced only minor changes in the phospholipid fractions. We concluded that a single nutritional regimen can effectively decrease the serum lipids and normalize the lipoprotein composition of type IV hypertriglyceridemic patients.

Elevated level and underdeveloped fatty acid composition of brain cholesterol esters in malnourished children

The content and fatty acid composition of cholesterol esters were measured in the forebrain, cerebellum, and brain stem of children who died within the first 2 years of life from severe malnutrition syndrome of kwashiorkor, marasmus, or marasmic kwashiorkor. All three brain regions of the malnourished children had elevated concentrations of cholesterol esters, compared to those of apparently normal, well-nourished children of comparable ages. This was particularly true for the brain stem, in which the elevation in some cases was 10-fold or more. In this brain region, and less pronouncedly also in the cerebellum, the elevations were more marked in the second year of life than in the first year. Fatty acid analysis showed that the developmental changes that are seen in brain cholesterol esters during normal growth, for example, fall in percentage proportions of palmitic and oleic acids and a concomitant rise in the proportion of arachidonic acid, were absent in the brain regions of the malnourished children.

Omega-3 fatty acids increase the arachidonic acid content of liver cholesterol ester and plasma triacylglycerol fractions in the rat.

Recent studies have demonstrated that dietary fish oils rich in eicosapentaenoic acid (C20:5,omega 3) lower the content of arachidonic acid and its metabolites in plasma and tissue phospholipids. The present study examined the fatty acid composition of cholesterol ester and triacylglycerol fractions from plasma and livers of rats fed diets enriched with saturated fatty acids (beef tallow), alpha-linolenic acid (linseed oil) or eicosapentaenoic acid (fish oil). Feeding diets containing linseed oil or fish oil for 28 days increased arachidonic acid (C20:4,omega 6) levels in the cholesterol ester fraction of liver and in the triacylglycerol fraction of the plasma lipids. Plasma cholesterol esters were depleted of C20:4,omega 6 after feeding of the diet containing either linseed oil or fish oil. The changes in C20:4,omega 6 content cannot be explained by alterations in cholesterol ester or triacylglycerol pools of plasma and liver. These results suggest that the decrease in phospholipid C20:4,omega 6 content generally observed after fish oil consumption may be partly due to a shift of C20:4,omega 6 from phospholipid to the triacylglycerol and/or cholesterol ester pools in the same tissue. Triacylglycerols and cholesterol esters may therefore play a buffering role in the homeostatic maintenance of tissue phospholipid levels of arachidonic acid.

AN EPIDEMIOLOGIC APPRAISAL OF THE ASSOCIATIONS BETWEEN THE FATTY ACIDS ESTERIFYING SERUM CHOLESTEROL AND SOME CARDIOVASCULAR RISK FACTORS IN MIDDLE-AGED MEN

The relations between the fatty acids of cholesterol esters and some cardiovascular risk factors have been investigated in a sample of 3,348 middle-aged men examined at entry into the Paris Prospective Study 2. The partial associations between the risk factors and the various fatty acids have been evaluated using a special regression method that takes into account the structural dependencies among the percentages of fatty acids. The results show that palmitoleic acid is strongly associated with alcohol consumption and blood pressure and that its association with blood pressure is absent in nondrinkers. High density lipoprotein cholesterol and apolipoprotein A1 are negatively associated with palmitic and dihomogammalinolenic acids and positively associated with oleic and linoleic acids. An inverse relation of low density lipoprotein cholesterol and apolipoprotein B to these fatty acids is also observed. Simultaneous high levels of palmitic and dihomogammalinolenic acids and low levels of oleic and linoleic acids could then be related to profiles of lipids and apolipoproteins exposing one to a high risk of coronary heart disease. These associations may be of interest in interpreting the relations observed in other studies between the fatty acid composition of cholesterol esters or other lipids and coronary heart disease.

Serum fatty acids in 8-year-old Finnish boys: correlations with qualitative dietary data and other serum lipids

AbstractTo survey risk factors in coronary heart disease in Finnish children, fasting serum specimens from 244 healthy 8-yr-old boys were analyzed for the fatty acid composition of cholesterol esters (CE), triglycerides (TG), free fatty acids (FFA), and phospholipids (PL). A qualitative dietary survey was made by asking parents to answer a questionnaire including, among others, a question on the kind of fat usually used on bread by the child. The mean percentages of linoleate (18:2) in serum cholesterol esters, triglycerides, free fatty acids, and phospholipids were 53.1, 13.5, 11.5, and 22.7%, respectively, which represent an international average. The quality of dietary fat had a clear influence on serum fatty acids, eg, the content of 18:2 in CE was 56.8 ± 3.6% in boys using soft vegetable margarine and 50.5 ± 3.6% in those using butter. The former had also a marginally lower serum total cholesterol (4.87 ± 0.86 mmol/1) than the latter (5.08 ± 0.80 mmol/ 1). Serum total cholesterol showed significant negative correlations with the percentage of 18:2 in all four lipid fractions, the highest r values being with PL-18:2 (-0.41) and CE-18:2 (-0.24). Accordingly, serum cholesterol was lower in the highest CE-18:2 quartile (4.67 ± 0.76 mmol/1) compared with the lowest (5.30 ± 0.70 mmol/1; p < 0.001). The results indicate that when serum fatty acids are used as indicators of the quality of dietary fat, a negative association between polyunsaturated fat and serum cholesterol may be demonstrable even within a free-living population.

Myelin Membrane from Adrenoleukodystrophy Brain White Matter—Biochemical Properties

Adrenoleukodystrophy (ALD) is an X-linked progressive neurological disorder characterized by the accumulation of saturated very-long-chain fatty acids (C24 to C30) in lipids, especially cholesterol esters of the brain white matter and adrenal cortex. In the present study we have investigated the localization of accumulated cholesterol esters in brain white matter. During isolation of purified myelin membrane from regions of active demyelination, significant enrichment in cholesterol ester was found in two fractions, mainly in a low-density floating fraction and to a lesser degree in the purified myelin preparation. The fatty acid composition of cholesterol esters from both the ALD floating and myelin fractions was enriched approximately 10-fold in saturated very-long-chain fatty acids (greater than or equal to C24) compared with control preparations.

Effect of melinamide on the fatty acid composition of cholesterol esters in experimental hyperlipidemia in rabbits.

After induction of hyperlipidemia in rabbits by feeding a diet supplemented with cholesterol (500 mg/animal/day) for 3 weeks, melinamide (300, 1000 or 3000 mg/kg/day) was orally administered to the rabbits maintained on the cholesterol diet for the following 13 weeks. Concentration of cholesterol esters and the fatty acid composition of the esters in serum, liver, heart and aorta were investigated gas-chromatographically. In hyperlipidemic rabbits, serum and tissue levels of cholesterol esters were 15 times (heart) to 190 times (liver) higher than in normal rabbits, and the levels were decreased dose-dependently by melinamide treatment. At the highest dose (3000 mg/kg), serum cholesterol ester was lowered to normal level. The fatty acid composition of cholesterol esters in serum and tissues was markedly changed by cholesterol diet, and the ratio of linoleic acid (C18:2) to oleic acid (C18:1) was higher in melinamide treated rabbits than hyperlipidemic control. At the highest dose, the ratio was 1.4 in serum, and it was similar to that in normal rabbits. The normalization of the fatty acid composition of cholesterol esters by melinamide is thought to result from the reduction of serum cholesterol caused by inhibition of cholesterol absorption from the intestine.

Cholesterol esters in rat brain infected with acute measles encephalitis: concentration and fatty acid composition.

The present study deals with the concentration and fatty acid composition of cholesterol esters in rat brains infected experimentally with measles virus to induce acute encephalitis. The left side of the cerebrum, as well as other portions of the brain, when inoculated percutaneously contained a large amount of cholesterol esters. The major fatty acids from the esters in the brain were C16:0, C16:1, C18:0, and C18:1; those from the serum were C18:1, C18:2, and C20:4. This result indicates that cholesterol esters may not come from serum but can be synthesized in situ, even in the brain with acute viral infection.

Cholesterol esters of the human brain during fetal and early postnatal development: content and fatty acid composition.

Abstract: The content and fatty acid composition of cholesterol esters of the human brain during development from 13 weeks' gestation up to 26 months of age was studied. The three major brain areas, the forebrain, cerebellum, and the brain stem, were studied separately. The concentration of the esters in each brain region was the highest at the earliest fetal age of 13 weeks and fell during growth. However, transient rises in the concentration were observed, at about birth in the forebrain and at 4–5 months after birth in the cerebellum The peak concentration during the transient period (125–150 μg/g fresh tissue of forebrain and 100–125 μg/g of cerebellum) was similar to the concentrations observed in the two parts respectively during early fetal ages. The brain stem also showed similar transient peak at about a few weeks before birth, but only when the esters were expressed as amount per cell. In absolute terms, a clear transient period was evident in the forebrain between birth and 9 months, while in the cerebellum or the brain stem, the total amount of the esters increased up to about 1 year of age and then remained almost unchanged. The major fatty acids of the esters were palmitic, palmitoleic, stearic, oleic, linoleic and arachidonic acid. Most of these fatty acids showed certain changes in relative proportions during development. Thus, in the forebrain, palmitic and oleic acid decreased from about 32% and 40% (weight percentages) at 13–15 weeks of gestation to about 20% and 25% respectively at 26 months of age. During this period, linoleic and arachidonic acid increased from about 3% and S% to about 10% and 24%, respectively. Most of these changes occurred after birth. The cerebellum and the brain stem differed only slightly from the forebrain in either the fatty acid composition or the pattern of the developmental changes in the composition.

Administration of dehydroepiandrosterone enanthate to oophorectomized women - effects on sex hormones and lipid metabolism

Eight bilaterally oophorectomized women were given a depot injection of 200 mg DHEA-enanthate to study the effect on endocrine and lipid metabolism. A decrease in sex-hormone binding globulin (SHBG) and an increase in androstenedione was found 14 and 30 days after the injection. No changes could be detected in LH, FSH, oestrone, oestradiol or oestriol. Testosterone showed a tendency towards an increase. As compared to pre-treatment values, plasma lipids were unaltered after 30 days. A decrease in high density lipoproteins (HDL), cholesterol and in very low density lipoproteins (VLDL), free cholesterol, total cholesterol and phospholipids were seen in the lipid composition of the lipoproteins on day 30. These findings are in agreement with previous data reported after the administration of drugs with androgen-like effects. The relative fatty acid composition of plasma lecithin revealed only minor changes while the fatty acid composition of cholesterol esters indicated a decreased portion of essential fatty acids. These results suggest, in agreement with previous studies, an impaired endogenous cholesterol formation in the liver. The results from the analysis of the fatty acid composition of lecithin and cholesterol esters might indicate a decreased percentage of exogenous (dietary) cholesterol ester in plasma.

Very low density lipoproteins in normal and cholesterol-fed rabbits: lipid and protein composition and metabolism: Part 1. Chemical composition of very low density lipoproteins in rabbits

The lipid and apoprotein composition of very low density lipoproteins (VLDL) ( d < 1.019 g/ml) from normal and hypercholesteremic (h.c.) rabbits are compared. Significant changes are observed in the apoproteins, as well as in the fatty acid composition of cholesterol esters, and in the relative distribution of phospholipids. Apoproteins show a marked increase of peptides with slow mobility (R2 and R3), corresponding to arginine-rich proteins, both in the rabbit and in some types of human hyperlipoproteinemias (hypothyroidism and Fredrickson Type III). VLDL were separated into the two fractions, VLDL-1 and VLDL-2. Peptides of slow mobility were shown to be present in a higher concentration in VLDL-1. Cholererol esters of h.c. VLDL have a very high content of oleic acid, the 18 : 1/18 : 2 ratio being about three times higher than in normal VLDL. Phospholipid distribution in h.c. VLDL is characterized by an increase of sphingomyelin and decrease of phosphatidylethanolamine. The PC/Sph ratio is about one fifth that of normal. These changes in VLDL lipids are very similar to those occurring in the lipid composition of the atherosclerotic plaques in mammals.

A quantitative study on free cholesterol, cholesterol ester and total cholesterol content of human gingiva in different degrees of chronic marginal periodontitis (author's transl)

No report of lipids analysis of human gingiva in different degrees of chronic marginal periodontitis has so far appeared except OTA et al. of our department earlier reported. It was suggested that the content of cholesterol ester in human gingiva with periodontal disease revealed a tendency decrease.In the present study, the author investigated the measurement of content of free cholesterol, cholesterol ester and total cholesterol in the gingiva, that occured in association with the progress of chronic marginal periodontitis. At the same time, a qualitative analysis was also made to identify main fatty acid composition of cholesterol ester.A study material consisted of 19 males and 11 females, ranging from 18 to 50 in age, who were diagnosed as periodontitis in the department of periodontology, Nihon University Dental Hospital, and were divided into three clinical groups of P1, P2 and P3 by OKADA's classification. As controls, P0 group who were diagnosed as healthy gingiva consisted of 6 males and 4 females, ranging from 20 to 40 in age.The obtained gingival specimen was extracted for total lipids by FOLCH et al's method. An aliquot of total lipids was spotted on a Silicagel G glass plate. After developing, free cholesterol and cholesterol ester fractions were identified. Free cholesterol and cholesterol ester in appropriate areas of the individual fractions were then scraped off and re-extracted. Gas liquid chromatography was carried out for qualitative and quantitative analysis.Results were obtained as follows:1. The study on content of free cholesterol and total cholesterol in different degrees of chronic marginal periodontitis, there was no statistical significance among each clinical group.2. But the content of cholesterol ester revealed a tendency of decrease according to the severity of the disease, and it showed significantly different to compare P1 group with P2, P3 group.3. The main fatty acid composition of cholesterol ester was C14:0, C16:0, C16:1, C18:1 and C18:2. However, there was no change in different degrees of chronic marginal periodontitis.

Fatty acid composition of neutral lipids and phospholipids of enamel and dentine from human molars

Neutral lipids and phospholipids were extracted from enamel and dentine of human molars, hydrolysed and the fatty acid composition of cholesterol esters, triglycerides, free fatty acids plus mono- and di-glycerides and total neutral lipids were determined. Lecithin, sphingomyelin plus phosphatidyl serine and phosphatidyl inositol, phosphatidyl ethanolamine, phosphatidic acid plus cardiolipin and total phospholipid fatty acids were also analysed. The major fatty acids present were palmitic, stearic and oleic, palmitoleic and linoleic acids being major components in some phospholipids. The relative proportions of the fatty acids from both neutral and phospholipids were similar in dentine and enamel. Both qualitative and quantitative analyses were similar to those obtained from normal rat teeth.

Fatty acid composition of neutral lipids and phospholipids of enamel and dentine from rat incisors and molars

Neutral lipids and phospholipids were extracted from enamel and dentine of rat incisor and molar teeth, hydrolysed and the fatty acid composition of cholesterol esters, triglycerides, free fatty acids plus mono- and di-glycerides and total neutral lipids were determined. Lecithin, sphingomyelin plus phosphatidyl serine and phosphatidyl inositol, phosphatidyl ethanolamine, phosphatidic acid plus cardiolipin and total phospholipid fatty acids were also analysed. The major fatty acids present were palmitic, stearic and oleic, palmitoleic and linoleic acids being major components in some phospholipids. The relative proportions of the fatty acids from both neutral and phospholipids were similar in dentine and enamel and incisors and molars.

Fatty acid composition of serum lipids in hyper- and hypothyroidism.

ABSTRACT The fatty acid composition of cholesterol esters, phospholipids, and triglycerides of the serum has been studied in groups of hyperthyroid and hypothyroid women and also in control material matched for age. In hyperthyroidism, a decrease in the proportions of linoleic acid and an increase in the proportions of some saturated and mono-unsaturated fatty acids were observed. When absolute concentrations were considered, it appeared that the decrease in linoleic acid was almost equivalent to the entire decrease in total fatty acids in the serum of the hyperthyroid patients. In hypothyroidism no changes were noted in the proportions of linoleic, saturated and mono-unsaturated fatty acids, and the absolute concentrations reflected the general increase in serum lipids. It is believed that these findings may be explained by the changes in lipid turnover which are known to occur in disturbances of thyroid function. In hyperthyroidism, they lead to a linoleic acid deficiency, while a sparing effect must be operating in hypothyroidism. The finding of relatively high linoleic acid values combined with hyperlipaemia in hypothyroidism seems to be characteristic of the condition, since other types of hyperlipaemia are almost invariably combined with low percentages of linoleic acid. Results regarding arachidonic and eicosatrienoic acid are consistent with increased synthesis in hyperthyroidism, and decreased synthesis in hypothyroidism.