Thermal acclimation and dietary lipids alter the composition,but not fluidity,of trout sperm plasma membrane

The effect of a long-term adaptation of rainbow trout to 8 and 18°C combined with a corn oil-or a fish oil-supplemented diet on the characteristics of the spermatozoan plasma membrane was investigated. The experiment lasted up to 22 mon during which spermatozoa were collected from the mature males. Spermatozoan plasma membranes were isolated by nitrogen cavitation, and the cholesterol content, phospholipid composition and fatty acid pattern were investigated. Membrane viscosity was assessed on whole cells by electron spin resonance using spin-labeled phospholipids. Neither diet nor rearing temperature influenced the cholesterol content of the plasma membrane nor the phospholipid class distribution. The rearing temperature of the broodstock only slightly affected the phospholipid fatty acids. A minor decrease in 18∶0 and increase in monounsaturated fatty acids was observed for the cold-adapted fish. These modifications were not sufficient to affect membrane fluidity, and we conclude that trout spermatozoa do not display any homeoviscous adaptations in these conditions. On the contrary, the dietary fatty acid intake greatly modified the fatty acid profile of plasma membrane phospholipids. The fish oil-fed trout displayed a much higher n−3/n−6 fatty acid ratio than did the corn oil-fed ones, but the 22∶6n−3 levels remained unchanged. Modifications in plasma membrane composition by the diet were obtained although neither of the two diets was deficient in essential fatty acids. The enrichment in n−3 fatty acids, however, did not affect plasma membrane fluidity which was unchanged by the diets.     

The dietary regulation of stearyl coenzyme A desaturase activity and membrane fluidity in the rat aorta

Numerous studies have demonstrated that alterations in membrane composition or fluidity are often associated with alterations in the properties of membrane-bound enzymes. In order to obtain membranes of varying fluidity, rats were fed diets that were either fat-free or supplemented with 15% safflower oil, and two properties associated with aorta and liver microsomal membranes were selected for study: stearyl CoA desaturase activity, and fluidity as monitored by fatty acid composition and microviscosity (measured by fluorescence depolarization). If fluidity directly modulates desaturase activity, one would predict that a low fluidity would stimulate the desaturase activity. Ten times more desaturase activity is present in aorta microsomes from rats on a fat-free diet than in microsomes from rats on a safflower oil supplemented diet. However, on the fat-free diet, these aorta microsomes were more fluid than those of rats fed safflower oil supplemented diet. The fluidity of liver microsomal membranes was not altered in response to diet, despite significant changes in desaturase enzyme content. The contrasting evidence presented here suggests that no correlation exists between desaturase enzyme activity and membrane fluidity in the two tissues studies. We have demonstrated that the aorta has appreciable capacity to desaturate stearyl CoA and that dietary manipulation causes significant changes in aorta membrane fluidity that may be of sufficient magnitude to affect the overall metabolism of aorta cells.     

Effects of dietary proteins on linoleic acid desaturation and membrane fluidity in rat liver microsomes

The effect of dietary protein, casein (CAS) and soybean protein (SOY), on linoleic acid desaturation in liver microsomes was studied in rats. The activity of Δ6 desaturase in total and rough endoplasmic reticula (ER and RER) was significantly higher in the CAS group than in the SOY group. In ER and smooth endoplasmic reticulum, the steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene, when incorporated into the membrane, was decreased in the SOY group and accompanied by a reduction in the cholesterol/phospholipid (CHOL/PL) ratio, consistent with an increase in membrane fluidity. In a separate study, the effect of varying dietary proteins, CAS, milk whey protein, egg albumin, SOY, potato protein and wheat gluten, on the relationship between the Δ6 desaturase activity and microsomal membrane fluidity was also examined. The results indicated that the dietary protein-dependent change in the liver microsomal CHOL/PL ratio affected membrane fluidity, and subsequently the activity of Δ6 desaturase in liver microsomes. However, since dietary protein influenced the Δ6 desaturase activity in RER without influencing membrane fluidity, it is possible that some regulation might have taken place at the level of enzyme synthesis.     

The effect of dietary zinc deficiency on the lipid composition of the rat erythrocyte membrane

The effect of dietary zinc deficiency in the rat on the lipid composition of the erythrocyte membrane was determined. Weanling male Wistar rats were fed an egg whitebased diet containing <1.0 mg Zn/kg dietad libitum. Control rats were either pair-fed orad libitum-fed the basal diet suppelemented with 100 mg Zn/kg diet. A zinc refed group was fed the −Zn diet until day 18 and then pairfed the +Zn diet until day 21. The voluntary feed restriction associated with dietary zinc deficiency resulted in erythrocyte membranes that had depressed phospholipid/protein and elevated cholesterol/phospholipid ratios. Similarly, all feed restricted groups had elevated 22-carbon n−3 polyunsaturated fatty acid (PUFA) and depressed 22-carbon n−6 PUFA concentrations in alkenylacyl and diacyl glycerophosphoethanolamine, phosphatidylserine and phosphatidylcholine; they also had depressed 24∶2n−6 levels in sphingomyelin. The relative concentrations of phospholipids in the membrane was similar between −Zn and +Zn (ad libitum) groups; however, the −Zn group had significantly less phosphatidylserine relative to +Zn (pair-fed) controls.     

Effects of dietary marine oils and olive oil on fatty acid composition, platelet membrane fluidity, platelet responses, and serum lipids in healthy humans

The influence of various dietary marine oils and olive oil on fatty acid composition of serum and platelets and effects on platelets and serum lipids were investigated as part of an extensive study of the effects of these oils on parameters associated with cardiovascular/thrombotic diseases. Healthy volunteers (266) consumed 15 mL/d of cod liver oil (CLO); whale blubber oil (refined or unrefined); mixtures of seal blubber oil and CLO; or olive oil/CLO for 12 wk. In the CLO, seal oil/CLO, and whale oil groups, serum levels of eicosapentaenoic acid (EPA) were increased. In platelets, EPA was increased in the CLO, seal/CLO, and olive oil/CLO groups. The localization of n-3 polyunsaturated fatty acids in the triacylglycerols did not seem to influence their absorption. Intake of oleic acid is poorly reflected in serum and platelets. No significant differences in triacylglycerols (IG), total cholesterol, or high density lipoprotein cholesterol were observed, even though TG were reduced in the CLO, CLO/seal oil, and whale oil groups. Mean platelet volume increased significantly in both whale oil groups and the CLO/olive oil group. Platelet count was significantly reduced in the refined whale oil group only. Lipopolysaccharide-stimulated blood tended to generate less thromboxane B₂ in CLO, CLO/seal, and CLO/olive groups. The whale oils tended to reduce in vivo release of β-thromboglobulin. In conclusion, intake of various marine oils causes changes in platelet membranes that are favorably antithrombotic. The combination of CLO and olive oil may produce better effects than these oils given separately. The changes in platelet function are directly associated with alterations of fatty acid composition in platelet membranes.     

Effect of dietary fat on phospholipid class distribution and fatty acid composition in rat fat cell plasma membrane

The effect of dietary fats on phospholipid class distribution and fatty acid composition was studied in rat fat cell plasma membrane. Three groups of male Wistar weanling rats were fed for 8 wk three diets differing in the amount and nature of the fats: 1.5% sunflower oil (low fat control; LFC), 10% sunflower oil (high fat, unsaturated; HFU), 1.5% sunflower oil+8.5% cocoa butter (high fat, saturated; HFS). Plasma membranes were prepared from epididymal adipocytes. The amount and type of dietary fat significantly altered membrane phospholipid distribution. Phospholipid content was lowered with HFU as compared to LFC or HFS diets, but no changes were observed for cholesterol. Phosphatidylinositol (PI) and phosphatidylserine (PS) were less affected by dietary changes than were other phospholipid classes. Major changes were detected for phosphatidylcholine (PC), phosphatidylethanolamine (PE) and sphingomyelin (SM) contents. No large changes in PC and PE fatty acid compositions were observed between the LFC and HFS groups, but the HFU diet induced several changes. Correlations with plasma membrane 5′-nucleotidase activities are discussed.     

Effect of dietary lipids on the lipid composition and phospholipid deacylating enzyme activities of rat heart

Rats were fed lard-enriched (17%) or corn oil-enriched (17%) diets and were compared with rats fed a low fat (4.5%) diet. Cardiac protein, DNA, phospholipid (PL) and fatty acid (FA) compositions were analyzed. Neutral phospholipase A, lysophospholipase and creatine kinase activities in the membrane and cytosolic compartments were also investigated. No significant modification of cardiac protein, DNA nor PL was observed among the three groups. Some alterations appeared in the FA composition. A lard-enriched diet induced a significant increase of 22∶5n−3 and 22∶6n−3 in heart phosphatidylcholine (PC) and phosphatidylethanolamine (PE), whereas a linoleic acid-rich diet induced a specific increase of 22∶4n−6 and 22∶5n−6 in these two major PL. Compared to rats fed the low fat diet, membrane-associated phospholipase A activity, measured by endogenous hydrolysis of membrane PC and PE, showed a significant increase (+45%) for both PL in rats fed corn oil. However, the activity of membrane-associated phospholipases, measured with exogenous [1-¹⁴C]dioleoyl PC, was not different among the three groups of rats. Cytoplasmic activity was decreased in rats fed corn oil, and lysophospholipase and creatine phosphate kinase activities were not significantly affected by diet. FA modification of the long chain n−6 FA induced by corn oil may be responsible for the observed increase in phospholipase activity. Physiological implications are suggested in terms of membrane degradation and prostaglandin production. Presented in part at the International Symposium on Lipid Metabolism in the Normoxic and Ischemic Heart, Rotterdam, The Netherlands, September 1986.     

Effect of early postnatal dietary sterculate on the fatty acid composition of rat liver and brain lipids

Pregnant rats were fed a high carbohydrate diet containing either 1% trilinolein or 1% trilinolein with 0.2% methyl sterculate from 18 day gestation to 21 day postpartum. The pups were weaned at 21 days and continued on the same diet for an additional 10 days. The microsomal stearyl CoA desaturase activities of the liver were effectively inhibited. Liver triglycerides showed increases in the saturated fatty acids concentrations at the expense of the corresponding monoenes. The concentration ofcis 6–7 octadecenoic acid was elevated. In liver phospholipids, the concentration of stearic acid was increased without a corresponding decrease in the oleic acid content. A drastic decrease in the nervonic acid (24∶1, n−9) concentration of liver sphingomyelin was observed. The lipids of the brain did not contain sterculic acid, and brain desaturase activity was unaffected. There was no significant change in the concentration of monoenoic acids from 16∶1 to 22∶1. However, nervonic acid was decreased by 32%. These results suggest that brain nervonic acid may be derived from a precursor other than oleic acid.     

The influence of dietary fat on the lipogenic activity and fatty acid composition of rat white adipose tissue

The in vivo fatty acid synthesis rate, selected enzyme activities and fatty acid composition of rat white adipose tissue from animals fed semisynthetic diets of differing fat type and content were studied. All animals were starved for 48 hr and then refed a fat-free (FF) diet for 48 hr. They were then divided into three groups. One group was continued on the FF diet for 48 hr. Another group was fed a diet containing 44% of calories from corn oil (CO). The final group was fed a diet containing 44% of calories from completely hydrogenated soybean oil (HSO). The animals on the FF diet had a marked increase in adipose tissue fatty acid synthesis during the 96-hr feeding peroid (as measured by³H incorporation into adipose fatty acids). Addition of either CO or HSO to the diets did not significantly inhibit fatty acid synthesis in dorsal or epididymal adipose tissue. The activities of the enzymes' fatty acid synthetase, ATP-citrate lyase and glucose-6-phosphate dehydrogenase increased on the FF diet and generally were not inhibited significantly by the addition of either fat to the diets. Linoleic acid was the major polyunsaturated fatty acid (ca. 22%) in adipose tissue. Monounsaturated fatty acids (palmitoleic, oleic,cis-vaccenic) made up ca 38% of the total adipose fatty acids, while saturated fatty acids accounted for about 32% (myristic, palmitic and stearic). White adipose tissue in mature male rats was a major depot for n−3 fatty acids. There were differences in the fatty acid composition of epididymal and dorsal adipose tissue, particularly in their content of long chain, polyunsaturated fatty acids with epididymal tissue containing more of these compounds than dorsal fat. The fatty acid composition of the white adipose tissue did not change significantly during fasting or 96 hr of refeeding the FF diets. The addition of HSO to the diet for 48 hr had little influence on the adipose tissue fatty acid composition, but the addition of CO to the diet caused a 7% increase in the dorsal adipose tissue linoleate content (as percentage of total dorsal adipose tissue fatty acids) within 48 hr compared to animals fed the stock diet and those starved for 48 hr. The fatty acid synthesis data indicated that adipose tissue in the rat can continue to be a source of de novo fatty acid synthesis in animals consuming high-fat diets.     

Effect of dietary palm oil and its fractions on rat plasma and high density lipoprotein lipids

Male Sprague Dawley rats were fed semipurified diets containing 20% fat for 15 weeks. The dietary fats were corn oil, soybean oil, palm oil, palm olein and palm stearin. No differences in the body and organ weights of rats fed the various diets were evident. Plasma cholesterol levels of rats fed soybean oil were significantly lower than those of rats fed corn oil, palm oil, palm olein or palm stearin. Significant differences between the plasma cholesterol content of rats fed corn oil and rats fed the three palm oils were not evident. HDL cholesterol was raised in rats fed the three palm oil diets compared to the rats fed either corn oil or soybean oil. The cholesterol-phospholipid molar ratio of rat platelets was not influenced by the dietary fat type. The formation of 6-keto-PGF_1α was significantly enhanced in palm oil-fed rats compared to all other dietary treatments. Fatty acid compositional changes in the plasma cholesterol esters and plasma triglycerides were diet regulated with significant differences between rats fed the polyunsaturated corn and soybean oil compared to the three palm oils.     

Red blood cell lipids and the plasma membrane

The red-blood cell occupies a unique position both in the historical development of membrane theory and current experimentation on membrane properties. The cell is readily accessible and has been studied in many animal species and disease conditions. Differences in composition, structure, and properties have been described, and a num-ber of highly specific cell types are now available for investigation. Several techniques are used to study the mem-brane of the intact cell. The membrane surface may be labeled in specific areas by the selective exchange of lipids such as cholesterol. Exchange studies provide information about lipid-lipid and lipid-protein interactions in the intact structure-Membrane lipids are hydrolyzed by phospho-lipases, and enzymatic activity is modified by the action of penetrating hemolytic agents. Perme-ability is readily measured by hemolysis and correlated with chemical structure, partition coefficient, and biological activity of different metabolites and drugs. The red cells of Vitamin B-deficient animals are particularly susceptible to hyperoxia. Hemolysis in these cells is correlated with alterations in membrane structure through the formation of lipid peroxides. Gorter and Grendel first used monolayers pre-pared from red-cell lipids to show that sufficient lipid was present in the membrane to form a bimolecular layer. Lipids extracts from the red cells of different animal species and disease states have been used in recent monolayer studies. The surface properties of these lipids and their purified neutral lipid and phospholipid fractions yield ad-ditional information about lipid-lipid interactions which may exist in the membrane. Enzyme hy-drolysis and penetration studies indicate that lipids in monolayers and membranes have similar properties.     

The effect of dietary fats on the plasma lipid composition of sheep

This study reports on the plasma lipid compositions of sheep fed either a control diet (C), a control diet supplemented with tallow (A) or polyunsaturated fatty acid (B) that had been protected against hydrolysis and hydrogenation in the rumen, or a control diet supplemented with maize oil (D). Diet B considerably increased the 18∶2 content of all the major plasma lipid fractions. Although the feeding of diet D also resulted in an increase in the 18∶2 contents within the cholesteryl ester, unesterified fatty acid, and phospholipid fractions the increases were considerably less than those observed with diet B; the levels of 18∶2 within the triglyceride fraction remained similar to that for the sheep which received the control diet. The effect of feeding diet A was confined solely to the triglyceride fraction where the concentrations of 16∶0 and 18∶1 were increased. The lipoproteins of the plasma were separated into very low density lipoproteins (d<1.006), low density lipoproteins (1.006<d<1.063), and high density lipoproteins (1.063<d<1.21), and the distribution of the major lipids between these lipoprotein fractions was investigated. Diet B increased considerably the proportion of triglyceride found in association with the very low density fraction and the concentrations of 18∶2 within all the lipoprotein fractions; these increases in the concentrations of 18∶2 were not confined to any particular lipid fraction of the lipoproteins. In contrast, the increases in the concentrations of 18∶2 produced as a result of feeding diet D were confined to the low and high density lipoproteins. The effect of feeding diet A was confined to fatty acid changes within the triglycerides of the low and very low density lipoproteins.     

Homeostatic control of membrane fatty acid composition in the rat after dietary lipid treatment

Diets in which both the lipid content and composition (polyunsaturated to saturated fatty acid ratio) were varied were fed to rats for 20 weeks, and the effects on the tissue lipid profiles were determined. The fatty acid profile of the plasma lipids, and the phospholipid fatty acids of the mitochondrial and microsomal fractions of liver, heart, kidney and brain, as well as erythrocyte membranes were determined. Despite large differences in the level and type of lipid present in the experimental diets and in the proportion of saturated fatty acids in the plasma lipids in response to the various diets, there was little effect on the proportion of saturated to unsaturated fatty acids in the phospholipids of the various membranes examined. The major effect of altering the dietary level of polyunsaturated to saturated fatty acids was on the ratio of the ω6/ω3 series of unsaturated fatty acids in the membrane lipids. This change occurred in all tissues except the brain, in which only a small response to altered dietary lipid intake was observed. The ω6/ω3 ratio was elevated upon feeding a diet rich in ω6 polyunsaturated fatty acids, but decreased when a diet rich in saturated fatty acids was fed. The failure to significantly alter membrane lipid saturation/unsaturation in the tissues examined would suggest that a homeostatic mechanism is operative in biological membranes and may act to buffer membranes from the effects of changes in the nature of the dietary lipid intake.     

Influence of dietary fiber on lipids and aortic composition of vervet monkeys

A semipurified, cholesterol-free diet containing 40% carbohydrate can produce aortic sudanophilia or aortic atherosclerosis in vervet monkeys (Ceroopithecus aethiops pygerethrus) depending on the particular carbohydrate fed. Four groups of vervet monkeys (three males and three females per group) were fed semipurified diets containing lactose. Two of the groups were also fed 15% cellulose (C) or 15% cellulose plus 0.1% cholesterol (CC); the two other groups were fed 15% pectin (P) or 15% pectin plus 0.1% cholesterol (PC). The average serum total cholesterol and low density lipoprotein cholesterol levels over the entire feeding period (mg/dl±SEM) were, for C, 156±14 and 95±5; for P, 173±15 and 112±8; for CC, 187±27 and 122±21; and for PC, 155±11 and 108±7. Cholesterol levels at autopsy (mg/dl±SEM) were, for C, 103±6; for P, 108±16; for CC, 92±9; and for PC, 106±7. Aortic sudanophilia (percentage of area) was, for C, 5.9±2.7; for P, 13.5±9.4; for CC, 5.3±2.1; and for PC, 21.6±10.3. Dietary pectin led to more severe sudanophilia (increased by 129% in the absence of cholesterol and by 308% in its presence) than did cellulose. Analysis of aortic glycosaminoglycans (GAG) revealed that dermatan sulfate levels fell in both cholesterol-fed groups, and chondroitin sulfate fell in aortas of group CC. Heparan sulfate levels were unaffected by cholesterol feeding. Hexuronic acid, galactosamine and hexosamine levels were elevated in the pectin-fed monkeys, but levels were unaffected by dietary cholesterol. Pectin may contribute galactosamine and glucuronic acid towards aortic GAG.     

The effect of dietary fat on the fatty acid composition of lipids secreted in rats' milk

During pregnancy and lactation, female rats were fed diets containing either 28% partially hydrogenated marine oil (28MO), 2% arachis oil (2AO), or no fat (FF). Milk lipid composition was examined by gas chromatographic analysis of the gastric content of 10-day-old suckling pups. An increase to 45% in the milk content of long chain monoenoic acids, 18∶1, 20∶1 and 22∶1, reflects the fatty acid composition of the marine oil. Milk fatty acids of medium chain length comprised 6%, 31% and 24% of total fatty acids in the (28MO), (2AO) and (FF) groups, respectively, suggesting that a high-fat diet (28MO) inhibits the lipid synthetic activity of mammary glands. The amount of dienoic C₁₈-acids (6%) in the group fed (28MO) containing no essential fatty acids (EFA) was similar to the amount of 18∶2 in the group receiving a low-fat, EFA-rich diet (2AO). However, only half the dienoic acid from the milk of the (28MO)-fed animals was linoleic acid, which was most likely mobilized from fat depots.     

The effect of dietary fat level and quality on plasma lipoprotein lipids and plasma fatty acids in normocholesterolemic subjects

This study examined the effect on the plasma lipids and plasma phospholipid and cholesteryl ester fatty acids of changing from a typical western diet to a very low fat (VLF) vegetarian diet containing one egg/day. The effect of the addition of saturated, monounsaturated or polyunsaturated fat (PUFA) to the VLF diet was also examined. Three groups of 10 subjects (6 women, 4 men) were fed the VLF diet (10% energy as fat) for two weeks, and then in the next two weeks the dietary fat in each group was increased by 10% energy/week using butter, olive oil or safflower oil. The fat replaced dietary carbohydrate. The VLF diet reduced both the low density lipoprotein (LDL)-and high density lipoprotein (HDL)-cholesterol levels; addition of the monounsaturated fats and PUFA increased the HDL-cholesterol levels, whereas butter increased the cholesterol levels in both the LDL- and HDL-fractions. The VLF diet led to significant reductions in the proportion of linoleic acid (18∶2ω6) and eicosapentaenoic acid (20∶5ω3) and to increases in palmitoleic (16∶1), eicosatrienoic (20∶3ω6) and arachidonic acids (20∶4ω6) in both phospholipids and cholesteryl esters. Addition of butter reversed the changes seen on the VLF diet, with the exception of 16∶1, which remained elevated. Addition of olive oil resulted in a significant rise in the proportion of 18∶1 and significant decreases in all ω3 PUFA except 22∶6 compared with the usual diet. The addition of safflower oil resulted in significant increases in 18∶2 and 20∶4ω6 and significant decreases in 18∶1, 20∶5ω3 and 22∶5ω3. These results indicate that the reduction of saturated fat content of the diet (<6% dietary energy), either by reducing the total fat content of the diet or by exchanging saturated fat with unsaturated fat, reduced the total plasma cholesterol levels by approximately 12% in normocholesterolemic subjects. Although the VLF vegetarian diet reduced both LDL- and HDL-cholesterol levels, the long-term effects of VLF diets are unlikely to be deteterious since populations which habitually consume these diets have low rates of coronary heart disease. The addition of safflower oil or olive oil to a VLF diet produced favorable changes in the lipoprotein lipid profile compared with the addition of butter. The VLF diets and diets rich in butter, olive oil or safflower oil had different effects on the 20 carbon eicosanoid precursor fatty acids in the plasma. This suggests that advice on plasma lipid lowering should also take into account the effect of the diet on the fatty acid profile of the plasma lipids.     

Effects of dietary linolenate on the fatty acid composition of brain lipids in rats

Weanling male rats were fed hydrogenated coconut oil to induce essential fatty acid (EFA) deficiency. After 15 weeks, the rats were divided into six groups. Five groups were fed graded amounts of purified linolenate (18∶3ω3) with a constant amount of linoleate (18∶2ω6) for six weeks. Fatty acid composition was determined in brain lipids. Increasing dietary 18∶3ω3 resulted in a decrease in arachidonic acid (20∶4ω6), docosatetraenoic acid (22∶4ω6) and docosapentaenoic acid (22∶5ω6), whereas 18∶2ω6 and eicosatrienoic acid (20∶3ω6) were increased both in total lipids and phospholipids. These results suggest that dietary 18∶3ω3 exerts its inhibitory effect mainly on the desaturation of 20∶ω6 to 20∶4ω6 in brain lipids. Linolenate was undetectable in brain lipids from any dietary treatments. The levels of eicosapentaenoic acid (20∶5ω3) in groups receiving dietary 18∶3ω3 were not different from that of the group receiving no 18∶3ω3. These results indicate that, in the brain, 18∶3ω3 is rapidly converted mainly to 22∶6ω3 without being accumulated and imply that dietary 18∶3ω3 can modulate the level of precursor of diene prostaglandins (PG) but not that of triene PG in the rat brain.     

Variations of fatty acid composition of erythrocyte and plasma lipids in the rat during the first period of life

The changes occurring in the fatty acid composition of the erythrocyte lipids during the first weeks of life were studied in the rat. The major changes consisted of a progressive decrease in oleic acid and a progressive increase in linoleic acid. A lower but significant increase in arachidonic acid was also observed. These changes are not related to variations in erythrocyte age; rather, they appear to be related to the age of the animal. Since somewhat similar changes were observed in the fatty acid composition of the major lipid classes of plasma during the first weeks of life, the possibility that these variations could account for the changes in the fatty acid composition of erythrocyte lipids was considered. Some support to this possibility was found in the results of experiments in which erythrocytes taken from 15-day-old rats were incubated with plasma taken from newborn rats. The changes in the fatty acid composition of erythrocytes and plasma lipids do not appear to be dependent on dietary lipids, since they occur during the suckling period, i.e., before the rats begin to ingest the pelleted diet which presents a fatty acid pattern completely different to that of the dams' milk.     

Major clofibrate effects on liver and plasma lipids are independent of changes in polyunsaturated fatty acid composition induced by dietary fat

The effects of clofibrate on the content and composition of liver and plasma lipids were studied in mice fed for 4 wk on diets enriched in n−6 or n−3 polyunsaturated fatty acids (PUFA) from sunflower oil (SO) or fish oil (FO), respectively; both oils were fed at 9% of the diet (dry weight basis). Only FO was hypolipidemic. Both oil regimes led to slightly increased concentrations of phospholipids (PL) and triacylglycerols (TG) in liver as compared with a standard chow diet containing 2% fat. Clofibrate promoted hypolipidemia only in animals fed SO. Its main effect was to enlarge the liver, such growth increasing the amounts of major glycerophospholipids while depleting the TG. SO and FO consumption changed the proportion of n−6 or n−3 PUFA in liver and plasma lipids in opposite ways. After clofibrate action, the PUFA of liver PL were preserved better than in the absence of oil supplementation. However, most of the drug-induced changes (e.g., increased 18∶1n−9 and 20∶3n−6, decreased 22∶6/20∶5 ratios) occurred inrrespective of lipids being rich in n−6 or n−3 PUFA. The concentration of sphingomyelin (SM), a minor liver lipid that virtually lacks PUFA, increased with the dietary oils, decreased with clofibrate, and changed its fatty acid composition in both situations. Thus. oil-increased SM had more 22∶0 and 24∶0 than clofibrate-decreased SM, which was significantly richer in 22∶1 and 24∶1.     

Effect of dietary polyunsaturated pork on plasma lipids and sterol excretion in man

Pork, enriched in linoleic acid content, was compared with conventional pork in the diet of three human subjects with respect to the plasma cholesterol concentration and the excretion in feces of neutral sterols and bile acids. Since the fatty acids in pork glyceride have an unusual positional distribution, the redistribution that might occur during the absorption and disposition of a fat meal was also studied. The plasma cholesterol was lower with polyunsaturated pork, the difference, 14 mg/100 ml plasma, being of the order expected from the change in polyunsaturated to saturated fatty acid ratio. On average, the excretion of neutral sterols was 57% greater with polyunsaturated than with conventional pork in all three subjects, and in this respect the results resembled the findings with polyunsaturated ruminant fats. During the absorption of pork fat, the high proportion of palmitate in the 2 position of lard triglyceride served as a useful marker, since human triglyceride carries mainly unsaturated fatty acids in that position. There were stepwise changes in the fatty acid composition at the 2 position of triglyceride as the fat was absorbed, transported through, and cleared from plasma, the palmitate being gradually replaced by oleate and linoleate. By contrast, the total fatty acid profile in the triglyceride changed relatively little, implying selective reacylation with palmitate at the 1 and/or 3 position. During the clearing of dietary triglyceride, the porcine triglyceride was thus converted to the form occurring in humans.