Lipoprotein lipase and lipogenic enzyme activities in adipose tissue from rats fed different lipid sources

This work was designed to study the effect of different lipid sources on the activities of lipoprotein lipase and lipogenic enzymes in adipose tissue from rats fedad libitum or energy-controlled diets. Male Wistar rats were fed diets containing 40% of energy as fat (olive oil, sunflower oil, palm oil or beef tallow), for 4 wk. Underad libitum feeding no differences were found among dietary fat groups in final body weight, adipose tissue weights and total body fat. Under energy-controlled feeding, despite isoenergetic intake, rats fed the beef tallow diet gained significantly less weight than rats fed the other three diets. Beef tallow fed rats showed the lowest values for adipose tissue weights and total body fat. When rats had free access to food no effect of dietary lipid source on lipogenic enzyme activities was found. In contrast, under energy-controlled feeding rats fed the beef tallow diet showed significantly higher activities of glucose-6-phosphate dehydrogenase and fatty acid synthase than rats fed the other three diets. Heparin-releasable lipoprotein lipase activity in perirenal and subcutaneous adipose tissues was not different among rats fed olive oil, safflower oil, palm oil or beef tallow. When comparing both adipose tissue anatomical locations, significantly higher activities were found in subcutaneous than in perirenal fat pad independently of dietary fat. In conclusion, under our experimental protocol, lipogenesis in rat adipose tissue does not seem to be affected by dietary fat type.     

Iron utilization and liver mineral concentrations in rats fed safflower oil, flaxseed oil, olive oil, or beef tallow in combination with different concentrations of dietary iron

Diets with a higher proportion of polyunsaturated fatty acids (i.e., linoleic acid) have decreased iron absorption and utilization compared with diets containing a higher proportion of the saturated fatty acid stearic acid (e.g., beef tallow). However, less is known regarding the influence of other polyunsaturated or monounsaturated fatty acids, along with higher dietary iron, on iron absorption and utilization. The present study was conducted to compare the effects of dietary fat sources known to vary in (n-3), (n-6), and (n-9) fatty acids on iron utilization and liver mineral concentrations. Male weanling rats were fed a diet containing 10, 35, or 100 μg/g iron in combination with saffower oil, flaxseed oil, olive oil, or beef tallow for 8 wk. Indicators of iron status, iron utilization, and liver iron concentrations were unaffected by an interaction between the fat source and iron concentration. Plasma copper was the only variable affected by an interaction between the fat source and dietary iron. Findings of this study demonstrate that flaxseed oil and olive oil may alter tissue minerals and affect iron utilization. Further studies should be conducted to establish the effect of varying (n-3), (n-6), and (n-9) fatty acids on trace mineral status and iron utilization. Data were presented in part at Experimental Biology 2000 as a poster session. A. D. Shotton and E. A. Droke, Dietary fat and iron modify immune function, FASEB J. 14, A239 (2000).     

Fish oil reduces cholesterol and arachidonic acid content more efficiently in rats fed diets containing low linoleic acid to saturated fatty acid ratios

Rats were fed diets containing a high level of saturated fatty acids (hydrogenated beef tallow) versus a high level of linoleic acid (safflower oil) at both low and high levels of fish oil containing 7.5% (w/w) eicosapentaenoic and 2.5% (w/w) docosahexaenoic acids for a period of 28 days. The effect of feeding these diets on the cholesterol content and fatty acid composition of serum and liver lipids was examined. Feeding diets high in fish oil with safflower oil decreased the cholesterol content of rat serum, whereas feeding fish oil had no significant effect on the cholesterol content of serum when fed in combination with saturated fatty acids. The serum cholesterol level was higher in animals fed safflower oil compared to animals fed saturated fat without fish oil. Consumption of fish oil lowered the cholesterol content of liver tissue regardless of the dietary fat fed. Feeding diets containing fish oil reduced the arachidonic acid content of rat serum and liver lipid fractions, the decrease being more pronounced when fish oil was fed in combination with hydrogenated beef tallow than with safflower oil. These results suggest that dietary n-3 fatty acids of fish oil interact with dietary linoleic acid and saturated fatty acids differently to modulate enzymes of cholesterol and fatty acid metabolism.     

Interactions of saturated, n-6 and n-3 polyunsaturated fatty acids to modulate arachidonic acid metabolism

Anti-thrombotic effects of omega-3 (n-3) fatty acids are believed to be due to their ability to reduce arachidonic acid levels. Therefore, weanling rats were fed n-3 acids in the form of linseed oil (18:3n-3) or fish oil (containing 20:5n-3 and 22:6n-3) in diets containing high levels of either saturated fatty acids (hydrogenated beef tallow) or high levels of linoleic acid (safflower oil) for 4 weeks. The effect of diet on the rate-limiting enzyme of arachidonic acid biosynthesis (delta 6-desaturase) and on the lipid composition of hepatic microsomal membrane was determined. Both linseed oil- or fish oil-containing diets inhibited conversion of linoleic acid to gamma-linolenic acid. Inhibition was greater with fish oil than with linseed oil, only when fed with saturated fat. delta 6-Desaturase activity was not affected when n-3 fatty acids were fed with high levels of n-6 fatty acids. Arachidonic acid content of serum lipids and hepatic microsomal phospholipids was lower when n-3 fatty acids were fed in combination with beef tallow but not when fed with safflower oil. Similarly, n-3 fatty acids (18:3n-3, 20:5n-3, 22:5n-3, and 22:6n-3) accumulated to a greater extent when n-3 fatty acids were fed with beef tallow than with safflower oil. These observations indicate that the efficacy of n-3 fatty acids in reducing arachidonic acid level is dependent on the linoleic acid to saturated fatty acid ratio of the diet consumed.     

Manganese absorption and retention in rats is affected by the type of dietary fat

There is evidence that manganese (Mn) metabolism may be altered by the form and amount of dietary fat. Also, iron (Fe) absorption is greater with saturated fats, as compared to polyunsaturated fatty acids (PUFAs). The absorption of Fe and Mn are interrelated in many aspects; therefore, the form of dietary fat may indirectly alter Mn absorption. The reported studies were conducted to determine whether saturated fat, as compared to unsaturated fat, affected Mn absorption, retention, and metabolism. In experiment I, adult rats were fed diets containing either 0.7 or 100.4 μg/g Mn with the fat source as high-linoleic safflower oil or stearic acid. After 2 wk of equilibration, the animals were fed a test meal of ⁵⁴Mn followed by whole-body counting for 10 d. Manganese absorption was significantly (p<0.05) lower in the stearic acid group (0.9–4.8%) than in the safflower oil group (20–33.8%); however, the biological half-life was shorter in the safflower oil group. Retention of ⁵⁴Mn and total Mn was always significantly (p<0.05) greater in the safflower oil group when dietary Mn was low, but it was the same when dietary Mn was high. In experiment II, weanling rats were fed 1.3, 39.3, or 174.6 μg Mn/g and either stearate, high-oleic safflower oil or high-linoleic safflower oil for 8 wk. Long-term feeding of the stearate and low Mn-containing diet resulted in a significant (p<0.0001) reduction in heart superoxide dismutase activity and kidney and liver Mn concentrations compared to the other diets. These data show that stearic acid inhibitits Mn absorption, but it may not inhibit Mn retention when dietary Mn is high. The U.S. Department of Agriculture, Agricultural Research Service, Northern Plains Area, is an equal opportunity/affirmative action employer and all agency services are available without discrimination. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

The control of lipogenesis by dietary linoleic acid and its influence on the deposition of fat.

The replacement of dietary starch by sucrose results in an increase in hepatic lipogenesis in the rat. When corn oil (4% by weight or 9% of the energy content of the diet) was included with the sucrose (20% by weight, 20% of the energy content) the lipogenic effect of the sucrose was completely suppressed. In contrast, when beef tallow replaced the corn oil, the induced activity caused by the sucrose was reduced by only approximately 20%. No significant differences were observed between males and females. These diets containing sucrose supplemented with either 4% (w/w) corn oil or 4% (w/w) beef tallow, were then used to ascertain whether or not the effects on hepatic lipogenesis were reflected in changes in the amount of fat deposited during growth from 4--24 weeks of age. It was shown that the percentage body fat was only statistically different (P less than 0.05) when animals fed sucrose-supplemented diets were compared with animals fed diets supplemented with sucrose and beef tallow. However, there were no significant differences in total carcass weight of these rats. The results are discussed in terms of the relative contribution of liver and adipose tissue to total lipogenesis and the factors which control the lipogenic activity in the two tissues.     

Dietary fish oil administration retards the development of hypertension and influences vascular neuroeffector function in the stroke prone spontaneously hypertensive rat (SHRSP).

An influence of fish oils (rich in eicosapentaenoic acid, EPA) in modulating (a) the development of hypertension in the stroke prone spontaneously hypertensive rat (SHRSP) and (b) vascular neuroeffector mechanisms in the SHRSP was explored. Rats (SHRSP) were placed on a series of diets for a period of 13 weeks from 4 weeks of age. The fatty acid composition of the diets was derived from fish oil, olive oil, safflower oil or beef fat. After 13 weeks, rats fed diets containing fish oil (at a total dietary fat level of either 5% or 15%) had mean blood pressures approximately 20-25 mmHg lower than other SHRSP rats maintained on diets containing either olive oil, safflower oil or beef fat. The dietary schedules providing fish oil depressed the contractile responses mediated by sympathetic nerve stimulation in the mesenteric vascular bed preparation. The results suggest that the n-3 polyunsaturated fatty acids retard the development of hypertension in the SHRSP rat and modulate the contractile responses of blood vessels mediated by sympathetic nerves in the isolated perfused mesenteric vascular bed preparation.     

Tissue fatty acid deposition is influenced by an interaction of dietary oil source and energy intake level in rats

To investigate the net tissue fatty acid deposition in response to graded levels of energy restriction and modification of diet fatty acid composition, rats were randomly assigned into four dietary groups and fed for 10 weeks diets containing 40% as energy of either fish, safflower, or olive oil, or beef tallow, consumed ad libitum or energy restricted to 85% or 68% of ad libitum intake by reducing diet carbohydrate content. An additional eight rats were killed before the diet regimen, to provide baseline data from which fatty acid deposition rates were calculated. Body weight, and heart, liver and fat mass gains were decreased with energy restriction (P<0.001). Olive oil feeding resulted in higher body weight gain (P < 0.03) than tallow feeding, whereas fish oil feeding was associated with highest (P < 0.007) liver weight and lowest (P < 0.03) fat mass gains. Energy deficit-related differences in the deposition of stearic, linoleic, arachidonic, and docosahexaenoic acids in heart and palmitic and docosahexaenoic acids in liver were dependent on the dietary oil consumed (P < 0.03). Similarly, interactive effects of restricted food intake and dietary oil type were found in the gain of palmitic, stearic, oleic, and linoleic acids in adipose tissue (P < 0.01) when expressed in relation to the amount of each fatty acid consumed. These data suggest that energy intake level can influence the deposition pattern, as well as oxidation rate, of tissue fatty acids as a function of tissue type, fatty acid structure, and dietary fatty acid composition.     

Influence of dietary safflower oil and tallow on growth, plasma lipids and lipogenesis in rats, pigs and chicks.

Rats, chicks and pigs were fed diets containing safflower oil or tallow. Plasma triglyceride levels were elevated when tallow, rather than safflower oil was added to the diet of rats, unchanged in chicks and lowered when tallow, rather than safflower oil was fed to pigs. The rate of fatty acid synthesis in rat and chick liver was higher, whereas the rate of lipogenesis in adipose tissue preparations from rats and pigs was lower when tallow, rather than safflower oil was fed. These results indicate that there are species-specific, as well as organ-specific, metabolic responses to various dietary fats.     

Increased hepatic activity of inducible nitric oxide synthase in rats fed on a high-fat diet

The effects were examined of the dietary level of fat on the activity of inducible nitric oxide synthase (iNOS) in the liver of rats. In experiment 1, rats were fed on a diet containing 5% or 20% beef tallow or safflower oil for 32 d. The animals were given a subcutaneous injection of the carcinogen, 1,2-dimethylhydrazine (DMH), on d 4. The activity of hepatic iNOS was significantly elevated by the high-fat diet, but was unaffected by the dietary source of the fat examined. In experiment 2, rats were fed on a 5% or 20% beef tallow diet for 11 d or 32 d with or without the DMH treatment. Feeding the high-fat diet and DMH treatment caused higher activity of hepatic iNOS. In experiment 3, the high-fat diet elevated hepatic iNOS activity and the amount of its protein in the lipopolysaccharide-treated rats. The results suggest that hepatic NO production is enhanced by a high-fat diet.     

Effects of type of fat in the diet on iron bioavailability assessed in suckling and weanling rats

Differences in iron bioavailability from human milk and milk formulas may in part be due to differences in lipid composition. We investigated the short and long term effects of diets based on different fats [corn, coconut, olive, or soy oil, human milk fat (HMF) and a formula fat blend (FF)] on iron absorption in rats. Suckling rat pups dosed with 59Fe-labeled diets containing different fat sources were killed after 6 h, and blood and individual tissues were counted. Iron availability was estimated by % 59Fe in blood. Pups dosed with a more saturated fat (coconut oil) had a higher % 59Fe in blood than those fed other fat sources. Weanling rats were used to determine iron bioavailability from fat sources using both the hemoglobin repletion method and whole body counting. Hemoglobin regeneration was significantly higher for rats fed the HMF diet (8.4 +/- 0.5 g/dl) than from the FF diet (6.5+/-0.6 g/dl) or the corn oil diet (less saturated) (6.4 +/- 0.3 g/dl). Rats fed diets based on coconut oil (more saturated) had significantly higher % 59Fe retention (61.6 +/- 1.4) than rats fed diets based on FF (49.8 +/- 3.4). There was a significant positive association between oleic acid in the diet and oleic acid in the intestinal mucosa (r = 0.95, p < 0.05) and between linoleic acid in the diet and linoleic acid in the intestinal mucosa (r = 0.97, p < 0.05) suggesting that the dietary treatment altered the fatty acid composition of the brush border membrane. Our results suggest that saturated fats may increase iron absorption and that part of this may be achieved by changes in the fatty acid composition of the intestinal mucosa. Hemoglobin regeneration and % 59Fe retention data suggest that differences in iron absorption from infant diets may in part be due to differences in fat composition. Therefore, lipid composition of infant formulas should also be taken into consideration as a factor influencing iron bioavailability.     

The effects of diet on the esterification of glycerol phosphate, dihydroxyacetone phosphate and 2-hexadecylglycerol by homogenates of rat adipose tissue.

1. Male rats were fed for 5 weeks after weaning on a diet containing (by weight) 59% of starch or on diets that contained 39% of starch and 20% of either sucrose, beef tallow or corn oil. 2. The rats fed on the beef tallow consumed more energy than did the rats fed on the starch and sucrose diets. The rats fed on the corn oil drank less water than did the other groups of rats. 3. There were no significant differences between the four groups in terms of body-weight gain, epididymal-fat-pad weight and in the size, number and triacylglycerol content of the adipocytes in the fat-pads. 4. There was a significant correlation (P less than 0.001) between the activities of glycerol phosphate acyltransferase and monoacylglycerol acyltransferase in individual rats. Both of these activities were highest in the group fed on the high-starch diet and both correlated with the consumption of glucose by individual rats in the four groups. 5. The percentage of glycerol phosphate converted into diacylglycerol and triacylglycerol was positively correlated with the mean diameters, surface area and triacylglycerol content of the adipocytes for individual rats and was greates in the sucrose-fed rats. 6. The specific activity of dihydroxyacetone phosphate acyltransferase was highest in the rats fed on beef tallow. This activity was positively correlated with the energy intake for all dietary groups over the 5-week feeding period. 7. The results are discussed in terms of the functions of the three routes of glycerolipid synthesis in adipose tissue.     

Dietary Stearic Acid Leads to a Reduction of Visceral Adipose Tissue in Athymic Nude Mice

Stearic acid (C18:0) is a long chain dietary saturated fatty acid that has been shown to reduce metastatic tumor burden. Based on preliminary observations and the growing evidence that visceral fat is related to metastasis and decreased survival, we hypothesized that dietary stearic acid may reduce visceral fat. Athymic nude mice, which are used in models of human breast cancer metastasis, were fed a stearic acid, linoleic acid (safflower oil), or oleic acid (corn oil) enriched diet or a low fat diet ad libitum. Total body weight did not differ significantly between dietary groups over the course of the experiment. However visceral fat was reduced by ∼70% in the stearic acid fed group compared to other diets. In contrast total body fat was only slightly reduced in the stearic acid diet fed mice when measured by dual-energy x-ray absorptiometry and quantitative magnetic resonance. Lean body mass was increased in the stearic acid fed group compared to all other groups by dual-energy x-ray absorptiometry. Dietary stearic acid significantly reduced serum glucose compared to all other diets and increased monocyte chemotactic protein-1 (MCP-1) compared to the low fat control. The low fat control diet had increased serum leptin compared to all other diets. To investigate possible mechanisms whereby stearic acid reduced visceral fat we used 3T3L1 fibroblasts/preadipocytes. Stearic acid had no direct effects on the process of differentiation or on the viability of mature adipocytes. However, unlike oleic acid and linoleic acid, stearic acid caused increased apoptosis (programmed cell death) and cytotoxicity in preadipocytes. The apoptosis was, at least in part, due to increased caspase-3 activity and was associated with decreased cellular inhibitor of apoptosis protein-2 (cIAP2) and increased Bax gene expression. In conclusion, dietary stearic acid leads to dramatically reduced visceral fat likely by causing the apoptosis of preadipocytes.     

Dietary mold oil rich in gamma linolenic acid increases insulin-dependent glucose utilization in isolated rat adipocytes

Effects of dietary fats differing in fatty acid composition on insulin-stimulated glucose metabolism in adipocytes isolated from rat white adipose tissue were compared. Rats were fed experimental diets containing various fats differing in fatty acid composition for 7 days. In the first experiment, rats were fed palm oil mainly consisting of palmitic (45.3%) and oleic acids (39.1%) or safflower oil rich in linoleic acid (71.6%). In the second trial, rats were fed palm oil, or a fat mixture rich in linoleic acid or mold oil rich in gamma-linolenic acid. Contents of fatty acids except for linoleic and gamma-linolenic acid were comparable between the fat mixture and mold oil. The former was devoid of gamma-linolenic acid and contained 42.0% linoleic acid, while the latter contained 25.9% gamma-linolenic and 15.7% linoleic acids. In the first experiment, the insulin-dependent increase in glucose oxidation and incorporation into lipids was higher in rats fed safflower oil compared to those fed palm oil. In the second experiment, the insulin-dependent increase in glucose oxidation and incorporation into lipids was higher in rats fed the fat mixture and mold oil than in those fed palm oil. However, the extent of the increase in these parameters was much greater in rats fed mold oil than in those fed the fat mixture. Therefore, dietary gamma-linolenic acid compared to linoleic acid increases glucose metabolism in response to insulin stimuli in isolated rat adipocytes.     

Stimulation of acyl-CoA oxidase by alpha-linolenic acid-rich perilla oil lowers plasma triacylglycerol level in rats

The effect of dietary polyunsaturated fatty acids (PUFA) on hepatic peroxisomal oxidation was investigated with respect to the postprandial triacylglycerol levels. Male Sprague--Dawley rats were fed semipurified diets containing either 1% (w/w) corn oil, or 10% each of beef tallow, corn oil, perilla oil, and fish oil for 4 weeks and 4 days. Hepatic and plasma triacylglycerol levels were reduced in rats fed fish and perilla oil diets compared with corn oil and beef tallow diets. The peroxisomal beta-oxidation, catalase activity, and acyl-CoA oxidase (AOX) activity were markedly increased by fish oil feeding. To a lesser extent, perilla oil elevated AOX activity in a 4-day feeding although the effect gradually decreased in a 4-week feeding. Similarly, the mRNA levels were increased in rats fed fish and perilla oils. AOX activity was negatively correlated with postprandial triacylglycerol levels. In addition, the stimulation of AOX was highly associated with the content of long chain n-3 PUFA such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in hepatic microsome. These effects were evident within 4 days of initiating feeding. Therefore, alpha-linolenic perilla oil exerts a similar effect to fish oil in stimulating hepatic activity and gene expression of AOX by enriching long chain n-3 PUFA in hepatic membrane fraction, which can partly account for the reduction of postprandial triglyceridemia.     

Differential effects of saturated fatty acids on low density lipoprotein metabolism in the guinea pig.

Studies have shown that dietary fat saturation affects guinea pig plasma low density lipoprotein (LDL) levels by altering both LDL receptor-mediated catabolism and flux rates of LDL (Fernandez et al. 1992. J. Lipid Res. 33: 97-109). The present studies investigated whether saturated fatty acids of varying chain lengths have differential effects on LDL metabolism. Guinea pigs were fed 15% (w/w, 35% calories) fat diets containing either palm kernel oil (PK), 52% lauric acid/18% myristic acid; palm oil (PO), 43% palmitic acid/4% stearic acid; or beef tallow (BT), 23% palmitic acid/14% stearic acid. Plasma LDL cholesterol levels were significantly higher for animals fed the PK diet (P < 0.001) with values of 83 +/- 19 (n = 12), 53 +/- 8 (n = 12) and 44 +/- 16 (n = 10) mg/dl for PK, PO, and BT diets, respectively. The relative percentage composition of LDL was modified by fat type; however, LDL diameters and peak densities were not different between diets, indicating no effect of saturated fatty acid composition on LDL size. ApoB/E receptor-mediated LDL fractional catabolic rates (FCR) were significantly lower in animals fed the PK diet (P < 0.01) and LDL apoB flux rates were reduced (P < 0.01) in animals fed the BT diet. A correlation was found between plasma LDL levels and receptor-mediated LDL catabolism (r = -0.66, P < 0.01). A higher apoB/E receptor number (Bmax), determined by in vitro LDL binding to guinea pig hepatic membranes, was observed for animals fed BT versus PK or PO diets and Bmax values were significantly correlated with plasma LDL levels (r = -0.776, P < 0.001). These results indicate that saturated fatty acids of varying chain length have differential effects on hepatic apoB/E receptor expression and on LDL apoB flux rates which in part account for differences in plasma LDL cholesterol levels of guinea pigs fed these saturated fats.     

Effects of dietary fat type and energy restriction on adipose tissue fatty acid composition and leptin production in rats

To investigate whether dietary fatty acid (FA) composition and energy restriction (ER) interactively influence obese (ob) gene expression, rats consumed diets containing beef tallow, safflower, or fish oil ad libitum (AL) or at 60% AL intake. Circulating leptin concentrations were higher (P < 0.0001) after AL feeding, but were not influenced by dietary fat. ER decreased (P < 0.0001) weight gain and visceral adipose weight, which were positively correlated (r = 0.40 P < 0.001, r = 0.58 P < 0.0001) with circulating leptin levels. Visceral adipose ob mRNA levels were greater in animals fed unsaturated fats, particularly safflower oil, which had the highest ob mRNA levels. Circulating leptin levels did not parallel ob mRNA levels, except for the greater abundance detected in AL adipose in comparison to ER animals. In addition, visceral FA profiles reflected dietary fat source and were influenced by an interaction of dietary fat and energy. These data demonstrate that dietary fat, particularly from a plant or marine source, and ER interactively influence ob mRNA levels; however, alterations in ob mRNA do not confer changes in circulating leptin, with the exception of ER, which is a key determinant. Thus, dietary intake is an important regulator of leptin production; however, the significance of these modest changes in diet-induced obese animals requires further study.     

Suppression of fatty acid synthase by dietary polyunsaturated fatty acids is mediated by fat itself,not by peroxidative mechanism

This study examined the effect of dietary polyunsaturated fatty acids (PUFA) that were supplemented with vitamin E on lipid peroxidation, glutathione-dependent detoxifying enzyme system activity, and lipogenic fatty acid synthase (FAS) expression in rat liver. Male Sprague-Dawley rats were fed semipurified diets containing either 1% (w/w) corn oil or 10% each of beef tallow, corn oil, perilla oil, and fish oil for 4 wk. Alpha-tocopherol was supplemented in perilla oil (0.015%) and fish oil (0.019%). Hepatic thiobarbituric acid reactive substances, an estimate of lipid peroxidation, were not significantly different among the dietary groups. The glutathione peroxidase, glutathione reductase, and glutathione S-transferase activities were all elevated by the polyunsaturated fats, especially fish oil. The activity of FAS was reduced in the polyunsaturated fat-fed groups in the order of fish oil, perilla oil, and corn oil. The mRNA contents decreased in rats that were fed the 10% fat diets, particularly polyunsaturated fats, compared with the rats that were fed the 1% corn oil diet. Similarly, the inhibitory effect was the greatest in fish oil. These results suggest that lipid peroxidation can be minimized by vitamin E; PUFA in itself has a suppressive effect on lipogenic enzyme.     

Dissociation of Large and Small Bovine Casein Micelles by Dialysis

The effects of dietary fat types on the thermogenic activity of brown adipocytes isolated from rat were examined. When beef tallow (saturated fatty acids + oleic) and safflower oil (linoleic) were the dietary fats, the respiration rates of brown adipocytes activated either by norepinephrine or an uncoupler of mitochondrial respiration (carbonylcyanide-m-chlorophenylhydrazone) were both slightly higher in rats fed the polyunsaturated fat. When the effects of safflower oil and evening primrose oil (linoleīc + γ-linolenic) were compared, the activated respiration rate tended to be higher in the latter. The respiratory responses to varying concentrations of norepinephrine were apparently dependent on the dietary fat types. Triglyceride stored in interscapular brown adipose tissue appeared to be modified by dietary fat types. Dietary fat also characteristically modified the fatty acid compositions of interscapular brown and epididymal white adipose tissues. Thus, the type of dietary fat caused an alteration to the thermogenesis of brown adipose tissue at the cellular level.     

Suppression of hepatic fatty acid synthase by feeding alpha-linolenic acid rich perilla oil lowers plasma triacylglycerol level in rats

This study was performed to determine the effects of dietary perilla oil, a n-3 alpha-linolenic acid (ALA) source, on hepatic lipogenesis as a possible mechanism of lowering triacylglycerol (TG) levels. Male Sprague-Dawley rats were trained for a 3-hour feeding protocol and fed one of five semipurified diets as follows: 1% (w/w) corn oil control diet, or one of four diets supplemented with 10% each of beef tallow, corn oil, perilla oil, and fish oil. Two separate experiments were performed to compare the effects of feeding periods, 4 weeks and 4 days. Hepatic and plasma TG levels were decreased in rats fed perilla oil and fish oil diets, compared with corn oil and beef tallow diets. The activities of hepatic lipogenic enzymes such as fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase, and malic enzyme were suppressed in the fish oil, perilla oil, and corn oil-fed groups, and the effect was the most significant in the fish oil-fed group. Also, the activities of glycolytic enzymes, glucokinase, and L-pyruvate kinase showed the similar trend as that of lipogenic enzymes. The activity of FAS, the key regulatory enzyme in lipogenesis, was positively correlated with hepatic and plasma TG levels and reduced significantly in the perilla oil-fed group compared with corn oil-fed group. In addition, the FAS activity was negatively correlated with the hepatic microsomal content of EPA and DHA. In conclusion, suppression of FAS plays a significant role in the hypolipidemic effects observed in rats fed ALA rich perilla oil and these effects were associated with the increase of hepatic microsomal EPA and DHA contents.