Effect of a diet rich in sunflower oil on aspects of lipid metabolism in the genetically-obese rat

POLYUNSATURATED FATTY ACID REGULATION OF GENES OF LIPID METABOLISM

Apart from being an important macronutrient, dietary fat has recently gained much prominence for its role in regulating gene expression. Polyunsaturated fatty acids (PUFAs) affect gene expression through various mechanisms including, but not limited to, changes in membrane composition, intracellular calcium levels, and eicosanoid production. Furthermore, PUFAs and their various metabolites can act at the level of the nucleus, in conjunction with nuclear receptors and transcription factors, to affect the transcription of a variety of genes. Several of these transcription mediators have been identified and include the nuclear receptors peroxisome proliferator-activated receptor (PPAR), hepatocyte nuclear factor (HNF)-4alpha, and liver X receptor (LXR) and the transcription factors sterol-regulatory element binding protein (SREBP) and nuclear factor-kappaB (NFkappaB). Their interaction with PUFAs has been shown to be critical to the regulation of several key genes of lipid metabolism. Working out the mechanisms by which these interactions and consequent effects occur is proving to be complicated but is invaluable to our understanding of the role that dietary fat can play in disease management and prevention.

Polyunsaturated fatty acids and gene expression in mammalian systems

Over the last 30 years it has become apparent that specific dietary fatty acids are capable of regulating, either directly or indirectly through various signal pathways, the expression of numerous genes, either positively or negatively. Such nutrient-gene interactions have important effects on cell metabolism, differentiation and growth, and ultimately on disease processes. The present review describes some of the more important fatty acid-gene interactions in relation to health and disease in mammalian species, and focuses on the underlying cell signal mechanisms, including various transcription factors, affected by fatty acids and some of their oxygenated derivatives, e.g. the eicosanoids. The review also attempts to clarify some of the complexities of the effects of fatty acids by suggesting a possible overriding regulation by the redox status of the cell. The latter will at least stimulate controversy in this exciting area of lipid research.

Cloning and characterization of bovine stearoyl CoA desaturasel cDNA from adipose tissues

Two overlapping cDNA clones have been isolated from bovine adipose tissue by the reverse-transcription-polymerase chain reaction (RT-PCR) method. The combined sequence of the two clones was 1039 bp in length and encoded 345 amino acids. The deduced amino acid sequence of the clones showed 96.5% similarity to that of sheep SCD and more than 88% similarities to other mammalian SCD1s, indicating that the clones are the cDNAs for the bovine SCD1. The transcript size of the bovine SCD1 was about 4.9 kb, the message was detected in the bovine adipose tissues but not in the liver. Female cattle expressed threefold higher levels of SCD1 mRNA than male animals.

Effects of a mixture of organisms, Lactobacillus acidophilus or Streptococcus faecalis on delta6-desaturase activity in the livers of rats fed a fat- and cholesterol-enriched diet

The effect of a mixture of organisms (a probiotic mixture) comprising Bacillus, Lactobacillus, Streptococcus, Clostridium, Saccharomyces, and Candida (10(7-8) colony-forming units/g rice bran of each component) on delta6-desaturase activity in liver microsomes was compared with those of Lactobacillus acidophilus and Streptococcus faecalis. There were four treatment groups. Each group of these rats received rice bran (control), the mixture of organisms, L. acidophilus, or S. faecalis (30 g/kg) along with a fat- and cholesterol-enriched diet for 4 wk. The serum total cholesterol concentration of the group fed the mixture of organisms was reduced by 15-33% compared with the other groups at the end of the 4-wk feeding period (P<0.05). The proportion of palmitic acid in the serum phosphatidylcholine (PC) for the control group was significantly higher than those of the other groups. The proportion of arachidonic acid in the serum PC for the mixed-organism group was also significantly higher than those of the other groups. The proportion of arachidonic acid in the liver PC for the mixed-organism group was significantly higher than those of the control and S. faecalis groups. The ratio of arachidonic acid/linoleic acid was significantly higher in the liver PC of rats fed the mixed organisms compared with the control group (P<0.05). The delta6-desaturase activity in the liver microsomal fraction of the mixed-organism group was significantly higher than those of the other groups. The delta6-desaturase activity correlated positively with the ratio of arachidonic acid/linoleic acid of liver PC, the correlation coefficient (r) being 0.819 (P<0.001). The results indicate that the effect of the mixture of organisms was to increase delta6-desaturase activity and serum arachidonic acid and decrease cholesterol compared to the other organisms and control, but the mechanism whereby the enzyme activity was related to serum cholesterol does not appear to have been explored.

Effect of selenium and vitamin E supplementation on lipid abnormalities in plasma, aorta, and adipose tissue of Zucker rats

Twenty-nine obese female Zucker rats (fa/fa) were fed with a laboratory chow supplemented or not with a selenium-rich yeast (Selenion), or Selenion + vitamin E, or vitamin E alone. Twelve lean female Zucker rats (Fa/Fa) of the same littermates fed with the same diet were used as control. After 32 wk of diet, obesity induced a large increase in plasma insulin and lipid levels. A significant decrease in the plasma vitamin E/triglycerides ratio (p<0.005) and an increase in plasma thiobarbituric reactive substances (TBARS) (p<0.005) were also observed. Plasma selenium and vitamin E increased in all supplemented rats. The plasma insulin level was decreased by selenion supplementation and the vitamin E/triglycerides ratio was completely corrected by double supplementation with Selenion + vitamin E. TBARS were also efficiently decreased in two obese groups receiving vitamin E. In plasma, adipose tissue and aorta, obesity induced an increase in palmitic acid (C16:0), a very large increase in monounsaturated fatty acids (palmitoleic acid C16:1, stearic acid C18:1) associated with a decrease in polyunsaturated n-6 fatty acids (linoleic acid C18:2 n-6, arachidonic C20:4 n-6). These alterations in fatty acid distribution were only partly modulated by Se and vitamin E supplements. However, in the aorta, antioxidant treatment in obese rats significantly reduced the increase in C16:0 and C16:1 (p<0.05 and p<0.01, respectively) and the decrease in arachidonic acid (p<0.05). These changes could be beneficial in the reduction of insulin resistance and help to protect the vascular endothelium.

Stearoyl-CoA desaturase activity in adipose tissues and liver of growing Large White and Meishan pigs

Stearoyl-CoA desaturase activity was measured in adipose tissue (backfat and neckfat) and liver microsomes of Large White and Meishan pigs. Preliminary assays have shown that delta 9-desaturase activity cannot be measured on frozen tissues, because freezing involves a loss in activity of 40-50%. The specific activity of liver delta 9-desaturase was much lower than that of the adipose tissues in both breeds, indicating that the liver is not a major site of oleate synthesis in the pig. The hepatic delta 9-desaturase activity was higher in Meishan than in Large White pigs. However, delta 9-desaturase activity in the adipose tissue of Large White pigs was much higher than that of Meishan pigs, even though the percentage of oleate was slightly higher in the adipose tissues of the latter. This investigation has demonstrated that differences in fatty acid composition of adipose tissues between Large White and Meishan pigs cannot be attributed to differences in delta 9-desaturase activity at this stage of maturity. These results suggest that the higher oleate percentage in Meishan adipose tissues would result from a higher delta 9-desaturase activity at an earlier age.

Inhibiting delta9-desaturase activity impairs triacylglycerol secretion in cultured chicken hepatocytes

The relationship between endogenous oleic acid produced by hepatic delta9-desaturase and the secretion of VLDL-triglycerides was investigated in a primary culture of chicken hepatocytes. When the fatty acid compositions of the secreted and intracellular triglycerides (TG) (or triacylglycerols) were compared, an imbalance between monoenes and saturated fatty acids was observed, with the secreted TG being significantly more unsaturated than the intracellular TG. The addition of a mixture of cyclopropenic fatty acids (specific inhibitors of fatty acid desaturation) to the culture medium of cells 24 h before measurement of their delta9-desaturase activity and TG secretion rate caused a significant impairment of both desaturase activity and TG secretion, without affecting total TG synthesis. However, the addition of oleic acid to the culture medium of cells treated with cyclopropenic fatty acids restored the TG secretion rate. Palmitic acid did not restore the TG secretion rate and linoleic acid partly restored the TG secretion rate. Finally, even in the presence of oleic acid in the culture medium of secreting cells, those which had been treated with cyclopropenic fatty acids had a significantly lower TG secretion rate than nontreated cells. Taken together, these results show that TG secretion is highly dependent on the delta9-desaturase activity and suggest that oversecretion of VLDL-TG in chickens and subsequent fattening could originate in a high hepatic delta9-desaturation of saturated fatty acids.

Differential expression of hepatic stearoyl-CoA desaturase gene 1 in male and female mice

The expression of hepatic stearoyl-CoA desaturase (SCD1) mRNA abundance and the fatty acid profile in male and female mice were compared. The expression of the SCD1 mRNA is significantly higher in female compared to male mice and that this difference is accompanied by higher levels of palmitoleic and oleic acid in the livers of female mice.

Age-related variations in plasma and liver lipids of Yoshida rats: a comparison with Wistar rats

Lipoprotein and liver lipids of spontaneously hyperlipidemic Yoshida rats were compared with those of normolipidemic Wistar animals for studying their age- and strain-related differences. Both strains showed an age-related increase in the total plasma cholesterol concentration. However, the Yoshida strain had a higher content of cholesteryl esters and triglycerides than the Wistar strain in both young and adult animals (2- and 8-month-old animals, respectively). The free cholesterol content was also higher, but only in the 8-month-old animals. Both strains showed an age-related increase in the proportion of HDL1 and a symmetrical decrease in both the HDL2 and HDL3 subfractions, but the variations were more evident in the Yoshida strain. The study of strain-related differences suggested that the spontaneous hypertriglyceridemia of the Yoshida strain was not only related to the higher amount and proportion of the VLDL fraction, but also to the higher content of triglycerides in the LDL fraction. The livers of Yoshida rats accumulated more triglycerides (with an age-related progression) than those of Wistar rats. The major lipid classes in the liver of Yoshida rats contained a significantly higher proportion of monounsaturated fatty acyls. Furthermore, this proportion showed an age-related increase in all the lipid classes, but in cholesteryl esters. This suggested that liver desaturases had a relevant role in the development of hyperlipidemia, and of its age-related variations, in the Yoshida strain.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipid metabolism in pigs fed beef tallow or high-oleic acid sunflower oil

The objectives of this study were to establish the effects of high-oleic sunflower oil (HOSO) and beef tallow on tissue fatty acids and stearoyl-CoA desaturase activities in swine; and to compare effects of HOSO and tallow on swine plasma triglycerides and lipoprotein-cholesterol fractions. Sixteen gilts were divided into two groups: eight fed a control diet containing 10 g/100 g beef tallow, and eight fed a diet containing 10 g/100 g HOSO. Plasma samples were obtained before feeding began and at 4 weeks and 8 weeks of dietary treatment. Samples were obtained from longissimus dorsi muscle, liver, adipose and duodenal mucosa for the measurement of fatty acid composition and stearoyl-CoA desaturase activity. The HOSO diet increased (P < 0.05) the concentrations (mumol/g wet weight of tissue) of 18:1 and 18:2 (n-6) in adipose tissue. In muscle from pigs fed the HOSO diet, concentrations of 14:0, 16:0, 16:1, 18:0, 18:1, and 18:2 (n-6) decreased (P < 0.05) relative to muscle from pigs fed the beef tallow diet; only 14:0 and 16:1 were reduced in liver by the HOSO diet. Stearoyl-CoA desaturase specific activity [(pmol 7 min-1 mg-1 microsomal protein)] was 40 percent lower, and activity expressed as pmol 7 min-1 g-1 tissue) was 20 percent lower, in adipose tissue of pigs fed HOSO (P < 0.05). No differences due to dietary treatment were observed for desaturase activity from muscle, liver or intestinal mucosa. Plasma triglycerides declined steadily in the tallow-fed pigs, possibly reflecting the lower percentages of liver 18:0 and 18:1 acids, relative to the HOSO-fed pigs. The animals responded similarly to the addition of fat (beef tallow or HOSO) to their diets with increased (P < 0.05) plasma total, LDL- and HDL-cholesterol by 4 weeks of treatment. Total cholesterol, LDL-, VLDL- or HDL-cholesterol were not different between pigs fed beef tallow or HOSO. Thus, differences in fatty acid composition of the diets were sufficient to alter tissue fatty acid composition and adipose tissue desaturase activity, but insufficient to alter plasma lipoprotein cholesterol.

Effect of dietary lipids and endocrine changes on polyunsaturated fatty acids in phospholipids of pancreas and brown adipose tissue of obese and lean rats

Obese (fa/fa) rats fed on control diet have lower proportions of linoleic acid (18:2n-6) and/or arachidonic acid (20:4n6) in IBAT and pancreas phospholipids compared with lean (Fa/-) rats. Lower stearic acid (18:0) to oleic acid (18:1n-9) mean ratios in fa/fa compared with Fa/- suggest enhanced delta 9-desaturase activity in the former. 18:2/20:4 mean ratios in pancreas, but not IBAT, are indicative of a reduced delta 6-desaturase activity in fa/fa rats. Absolute amounts of phospholipids (mg/unit tissue wt) were 2-fold greater in IBAT of fa/fa compared with Fa/- rats, irrespective of their diet. This was reflected in greater absolute amounts of 18:2n-6 and 20:4n-6 only in HSO and HTO fa/fa groups, but not in the control group. Adrenalectomy (Adx) or T3 treatment also modified phospholipid fatty acid composition of IBAT and pancreas phospholipids in animals fed on the control diet with fa/fa rats more sensitive to endocrine induced changes. In fa/fa rats T3 treatment increased docosahexaenoic acid (22:6n-3) in IBAT of both phenotypes compared with the control, but this effect was evident only in fa/fa and not Fa/- pancreas. T3 treatment also increased docosapentaenoic acid (22:5n-3) in IBAT from, both phenotypes, but no 22:5n-3 was evident in the pancreatic tissue of these animals. ADX also increased 22:6n-3 in the IBAT of fa/fa (Fa/- values were less than 1%) but not in the pancreas of fa/fa or Fa/-. ADX modified the relative proportions of 18:0 to 18:1 and 18:2 to 20:4 in IBAT and pancreas of fa/fa in a way that indicated decreased delta 9-desaturase and increased delta 6-desaturase activities; these effects tended toward normal again in pancreas of fa/fa rats on corticosterone replacement (CST).

Incorporation of delta 6- and delta 5-desaturation fatty acids in liver microsomal lipid classes of obese Zucker rats fed n - 6 or n - 3 fatty acids

The aim of this work was to study the effect of dietary n - 6 (as borage oil) and of n - 3 (as fish oil) fatty acids on the incorporation--in liver microsomal lipid classes--of fatty acids involved in delta 6- and delta 5-desaturations in obese Zucker rats compared with their lean littermates and with Wistar control rats. We observed that body and liver weights were decreased when obese Zucker rats were fed the fish oil diet. The major part of the radioactivity was recovered, in the obese Zucker rats, into the neutral lipids and especially into the triacylglycerols, while it was recovered into the phospholipid classes, especially into phosphatidylcholine, in the two other strains. Results show, in all phenotypes, an increased alpha-linolenic acid delta 6-desaturation in PL classes when the rats were fed the fish oil diet. However, a decreased linoleic acid delta 6- and delta 5-desaturation was observed in obese Zucker rats fed the fish oil diet. The fish oil diet favours the n - 3 fatty acid biosynthesis and incorporation into liver microsomal lipid classes to the prejudice of the n - 6 fatty acid series. The fatty acid incorporation is simultaneously regulated by the genetical phenotype and dietary fatty acids.

Liver stearyl-CoA desaturase activity and fatness in birds. In vitro studies in the growing turkey and chicken

1. Liver stearyl-CoA desaturase activity and total body fat were measured in 4-, 8- and 12-week-old turkeys and chickens reared together and fed either of two isocaloric diets differing in their protein content. 2. Chickens showed higher desaturase activity and body fatness as compared to turkeys. 3. These results have been discussed with special emphasis on the role of liver stearyl-CoA desaturase activity upon lipid transport and deposition in birds.

Impact of dietary fatty acid supplementation on renal injury in obese Zucker rats

We previously reported that renal injury in hyperlipidemic, obese Zucker rats was associated with a relative deficiency of tissue polyunsaturated fatty acids (PUFA). In the present study 10-week-old obese Zucker rats were pair fed regular chow or chow containing either 20% sunflower oil rich in n-6 PUFA, fish oil rich in n-3 PUFA, coconut oil medium-chain saturated fatty acid, or beef tallow long-chain saturated fatty acid. At 34 weeks of age there were comparable reductions in albuminuria, mesangial matrix expansion, and glomerulosclerosis in the fish oil and sunflower oil groups. While both fish oil and sunflower oil reduced serum triglycerides, and improved the composition of triglyceride-enriched lipoproteins, only fish oil decreased serum cholesterol. The effect of the dietary fatty acid supplementation on fatty acid profiles were similar in isolated glomeruli and cortical tissue. In general, the amelioration in injury in the fish oil and sunflower oil fed rats was most closely linked to glomerular levels of PUFA, either n-6 or n-3. These data suggest that hyperlipidemia and abnormalities in tissue FA are closely linked, and that dietary supplementation with PUFA may ameliorate chronic, progressive renal injury.

Regulation of polyunsaturated fatty acid metabolism in tissue phospholipids of obese (fa/fa) and lean (Fa/-) Zucker rats. 1. Effect of dietary lipids on cardiac tissue

The present investigation addressed three questions: (i) Does the obese syndrome alter the fatty acid composition of cardiac tissue and membrane phospholipids in obese (fa/fa) rats? (ii) Are changes, if they occur, similar to those reported for tissues of the genetically obese (ob/ob) mouse? (iii) Can cardiac tissue phospholipids and their component fatty acids be modified by dietary lipids and if so does this occur to the same extent in both fa/fa and lean (Fa/-) rats? Proportions of polyunsaturated fatty acids (PUFA) in cardiac total phospholipids of fa/fa rats differed significantly from those of Fa/- rats and from those reported for ob/ob mice. Increased 18:2n-6 and decreased 20:4n-6 and 22:6n-3 in fa/fa rats indicated impaired PUFA metabolism, possibly reduced delta 6 and/or delta 5 desaturase activity, compared with Fa/- rats. No differences in hepatic delta 6 and delta 5 desaturase activity between fa/fa and Fa/- were found but enhanced activity of delta 9 desaturase activity in fa/fa as compared to Fa/- was evident. Inclusion of sunflower oil (SO) or triolein (TO) at 5% and 20% by weight in the diet elicited marked changes in the fatty acyl composition of cardiac phospholipids in both fa/fa and Fa/- rats when compared with animals fed the control Oxoid diet alone. Supplementation with triolein was most effective, reducing 18:2n-6 and increasing 20:4n-6 proportions in fa/fa rats so that they resembled those in Fa/- rats fed the control Oxoid diet. The type of fat rather than the amount of its dietary intake appears to be the main determinant of the observed changes in phospholipid composition.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue phospholipid fatty acid composition in genetically lean (Fa/-) or obese (fa/fa) Zucker female rats on the same diet

The fatty acid composition of serum total lipids, of phospholipids of various organs (liver, heart, kidney), and of nervous structures (brain, retina, sciatic nerve, myelin, synaptosomes) have been compared in lean (Fa/-) and genetically obese (fa/fa) Zucker female rats. Both received a standard commercial diet including 37% of 18:2n-6 and 5% of n-3 polyunsaturated fatty acids (PUFA), 1.7% of which were in the form of 20:5n-3 and 22:6n-3. In comparison with lean rats, the results for the obese rats pointed out (i) no difference in the fatty acid composition of nervous structures; (ii) a decrease of 18:2n-6 (from -8% to -35%) and of 20:4n-6 (from -9% to -49%) in serum, liver and in kidney; this was compensated for by an increase in 20:3n-6 (from +30% to +320%) and in total n-3 PUFA (from +68% to +76%); (iii) a decrease of 20:4n-6 (-18%) and of 22:6n-3 (-24%) in heart compensated for by an increase in 18:2n-6 (+39%) and in 20:3n-6 (+233%); and (iv) constant levels of total PUFA (n-6 and n-3) in the various fractions studied, except in serum where this level decreased (-23%). Finally, except for the nervous structures, tissue phospholipids of obese rats included a lower proportion of 20:4n-6 and a higher proportion of 20:3n-6. This resulted in a significant reduction in the 20:4n-6/20:3n-6 ratio; by contrast, the 20:3n-6/18:2n-6 ratio increased. The results suggest that in Zucker rats, the obese character (fa/fa) affects the desaturation-elongation process of 18:2n-6 to 20:4n-6 by specifically decreasing delta 5-desaturase activity.

Delta 6 and delta 5 desaturase activities in liver from obese Zucker rats at different ages

delta 6 Desaturation of linoleic acid (18:2 n-6) and delta 5 desaturation of dihomo-gamma-linolenic acid (20:3 n-6) were measured in liver microsomes from genetically obese Zucker rats (fa/fa) and from their lean littermates (Fa/--). Both groups were fed a balanced commercial diet. The rats were 6, 9 and 12 weeks old, which corresponded to stages in their active growth period. The content of total fatty acids and n-6 polyunsaturated fatty acids in whole liver and liver microsomes was also determined in order to ascertain how the desaturase activities measured in vitro reflected regulation of essential fatty acid metabolism in vivo. Contrary to values obtained for delta 6 desaturation, delta 5 desaturation at nonsaturating substrate levels were lower in obese rats than in lean controls. In contrast, at saturating substrate level, the maximal delta 5 desaturase activities were the same in both phenotypes and they increased with age. Study of delta 5 desaturation kinetics (1/V vs 1/S) showed that Vm did not differ between 12-week-old obese and lean rats, whereas KM in obese rats was much lower than in controls, expressing the very low affinity of the enzyme for the substrate in obese animals. The fatty acid composition of liver lipids reflected the results of desaturase activities in vitro. In particular, the ratios 20:4 n-6/20:3 n-6 were lower in obese rats than in lean rats, which can be explained by the lower conversion of 20:3 n-6 into 20:4 n-6 by delta 5 desaturation.(ABSTRACT TRUNCATED AT 250 WORDS)

[Fatty acid composition of platelet phospholipids and plasma lipids in obese Zucker rats]

The purpose of this work was to see whether hyperlipaemia observed in genetically obese Zucker rats (fa/fa) was associated with differences in fatty-acid composition of plasma triacylglycerols, plasma phospholipids and of platelet phospholipids, in comparison with the control lean rats (Fa/-). Results showed that plasma triacylglycerols and phospholipids were increased in obese rats. In triacylglycerols, the amount of saturated and monounsaturated fatty acids was highly increased whereas the amount of the n-6 and n-3 polyunsaturated fatty acids was little modified. In plasma phospholipids, saturated and monounsaturated fatty acids were also increased, as were the n-3 fatty acids (except C 18:3 n-3); the n-6 fatty acids were little increased except C 20:3 n-6 which was markedly increased. These results concerning the amounts of fatty acids have their counterpart in their relative proportions of fatty acids. Data thus obtained suggest that conversion of linoleic acid (C 18:2 n-6) into arachidonic acid (C 20:4 n-6) was decreased in obese rats, particularly the delta 5 desaturation step. On the contrary, conversion of linolenic acid (C 18:3 n-3) into higher polyenes seemed increased. Thrombocytosis was not modified in the obese rat, but the volume of the platelets was increased. Platelet phospholipids exhibited the same modifications as plasma phospholipids but with different magnitude. Saturated and monounsaturated fatty acids were little augmented, n-3 fatty acids were more augmented (except C 18:3 n-3 acid which was unchanged); n-6 fatty acids were not modified except C 20:3 n-6 acid which was highly increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of sunflower seeds in grower diets for pullets and subsequent performance as affected by aureomycin and pelleting

In two experiments the effects of unhulled sunflower seeds (USFS) were evaluated at levels of 19 and 38% in corn-based diets for pullets between 10 and 19 wk of age. As an additional treatment a .09%-lysine monohydrochloride supplement was added to the 38% USFS-containing diet in Experiment 2. Isonitrogenous grower diets made up of corn and soybean meal or largely oats served as control diets. During the productive phase, layers were fed a high oats diet as mash (both experiments) or in pelleted form (Experiment 2). One half of the hens in each study were fed layer diets containing Aureomycin at 100 g per ton for 1 wk during each 28-day period to monitor the effect on egg production. Treatments during the laying phase were superimposed on the previous growing phase treatments. Pullets fed the 38% USFS diet in Experiment 1 were significantly lighter (P less than .01) at 19 wk of age and reached 50% egg production 2 days later than those on the control corn-soy diet. However, subsequent overall laying performance for 14 28-day periods was not significantly affected by the growing treatments. Neither growth nor laying performance was influenced by the treatments imposed during the rearing period of the second experiment. The two supplies of USFS varied considerably in crude fiber (14.6 vs 25.8%) and ether extract components (42.4 vs. 29.0%, respectively). The discrepancy in growth response to USFS of the two experiments was possibly related to the difference in the ether extract portions of the oil seeds. Egg production rate was significantly increased by Aureomycin only when the diet was pelleted.

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 period (as measured by 3H 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.(ABSTRACT TRUNCATED AT 250 WORDS)

n-3 Essential fatty acids decrease weight gain in genetically obese mice

1. Lean (ln/ln) and obese (ob/ob) mice were given diets containing a fat source of 100 g evening primrose (Oenothera biennis) oil (fatty acids 18:2n-6, 18:3n-6; EPO) or 100 g cod liver oil (20:5n-3, 22:6n-3; CLO)/kg diet. 2. Weight gain was lower in the ob/ob mice fed on CLO, an effect unrelated to food intake. 3. In the ob/ob mice fed on CLO, thromboxane synthesis by clotting platelets was reduced compared with that in ob/ob mice fed on EPO. 4. The ob/ob CLO-fed mice had lower arachidonic acid but higher levels of n-3 fatty acids in liver, brown adipose tissue and white adipose tissue. 5. The n-3 fatty acids in CLO therefore replaced the n-6 fatty acids in tissue lipids and reduced synthesis of '2 series' prostaglandins in addition to causing lower weight gain in the CLO-fed ob/ob mice.

Effects of dietary triolein and sunflower oil on insulin release and lipid metabolism in Zucker rats

Obese and lean male Zucker rats were fed ad libitum on diets containing either 50 (L) or 200 (H) g/kg diet of either triolein (T) or sunflowerseed oil (S). The specific activity of the hepatic microsomal delta 9 desaturase enzyme was depressed in both lean and obese rats fed the HS diet compared with the other three diets. The fatty acid composition of liver and subcutaneous white adipose tissue lipids were consistent with a lower delta 9 desaturation activity in rats fed the H diets, particularly for the HS diet. In both genotypes, microsomal delta 9 desaturase activity and the ratio of 16:1/(16:0 + 16:1) fatty acids in liver lipids were inversely related to the proportion of 18:2 in liver lipid. Plasma insulin concentrations and rates of glucose-stimulated insulin release in vivo were higher in obese rats compared with lean rats, and plasma insulin levels were higher in rats fed S compared with T. There was no relationship between delta 9 desaturase activity and either plasma insulin concentration or rates of insulin release in vitro. These findings suggest that hepatic delta 9 desaturase activity of Zucker rats is responsive to changes in the proportion of 18:2 in liver lipids but is not affected by changes in insulin secretion.

Changes in lipid metabolism in diet-induced obesity

Mature male Sprague-Dawley rats fed a powdered Purina Chow diet containing corn oil and condensed milk (CM) were compared to rats fed a Purina Chow diet (control). CM rats gained more weight and consumed more calories over a 73-day period than the control rats. The increased weight gain and body fat in CM rats was accompanied by increased cell number in retroperitoneal and inguinal but not epididymal fat pads while cell size was unchanged in all three pads. After obesity had developed there was an increase in insulin levels, lipolysis, hepatic fatty acid synthesis, and fatty acid oxidation. While CM rats demonstrated hyperinsulinemia and hyperglycerolemia, they maintained normal glucagon and glucose levels. They demonstrated higher rates of fatty acid synthesis in isolated hepatocytes but not in vivo, suggesting that a greater potential for fatty acid synthesis in CM rats was masked in vivo by the inhibitory action of dietary lipids. Beta-oxidation of (1-14C) palmitate in vivo and in vitro, and in vivo ketogenesis were greater in CM than in chow fed rats. These studies demonstrate that, after the development of obesity, CM rats, like genetically obese Zucker rats, are hyperinsulinemic and have elevated levels of fatty acid synthesis. However, unlike obese Zucker rats, CM rats displayed an increase in beta-oxidation. These studies suggest that increased insulin levels and hepatic fatty acid synthesis may contribute to dietary obesity (as they do to genetic obesity), whereas increased fatty acid oxidation in dietary obesity may be a compensatory response to maintain a lower body weight.

Essential fatty acids in the liver and adipose tissue of genetically obese mice: effect of supplemental linoleic and gamma-linolenic acids

Genetically obese mice (ob/ob) and their lean litter-mates were given diets iso-energetically supplemented with sucrose, hydrogenated coconut oil, safflower oil or evening primrose (Oenothera biennis) oil. Weight gain over 15 weeks was significantly greater in the evening primrose oil-supplemented obese mice than in the other groups. In all the groups of obese mice, liver total phospholipids contained proportionally less linoleic acid and more dihomo-gamma-linolenic acid and arachidonic acid than did the lean controls. As a percentage of total fatty acids, n-3 essential fatty acids (EFA) in liver and adipose tissue lipids were significantly lower in the obese mice than in the lean controls. Supplementation with EFA-rich oils (safflower and evening primrose oil) increased the proportional composition of n-6 EFA and decreased the n-3 EFA more in the liver total phospholipids of the lean than the obese mice.

Hepatic delta 6-desaturase activity in lean and genetically obese ob/ob mice

Hepatic delta 6-desaturase activity is primarily located in the mitochondrial fraction in mice. Both delta 6- and delta 5-desaturase activities are increased in the liver of young (6-week-old) obese mice. The increase in hepatic delta 6-desaturase activity in obese mice does not occur until weaning. Neither restriction of food intake nor hyperinsulinaemia normalize hepatic delta 6-desaturase activity of obese mice. Both cold acclimation and tri-iodothyronine (30 micrograms/day per kg) decreased hepatic delta 6-desaturase activity of obese mice to levels observed in lean mice, whereas the increase in activity in obese mice was still maintained after the induction of hypothyroidism.

The regulation of hepatic stearoyl-coenzyme A desaturase in obese-hyperglycaemic (ob/ob) mice by food intake and the fatty acid composition of the diet

1. The effects of food intake and the fatty acid composition of the diet on the hepatic stearoyl-CoA desaturase activity of obese-hyperglycaemic (ob/ob) mice were investigated. 2. Obese mice fed on a commercial mouse diet, ad libitum, had 6.5-fold more activity per liver cell than had lean mice. 3. On a diet containing 14% corn oil the activity was 65% less in obese mice and 62% less in lean mice compared with animals fed on the commercial diet. 4. Feeding with 14% saturated fat in the diet doubled the activity in lean mice compared with those on the commercial diet, but had no effect on the activity in obese mice. 5. Obese mice fed on the corn-oil diet contained a higher proportion of linoleic acid in the liver lipids than did lean mice fed on the commercial diet, but the acyl-CoA desaturase activity was 125% higher than in the lean mice. 6. Limiting the food intake of obese mice by pair-feeding with lean mice decreased their acyl-CoA desaturase activity when the animals were fed on the saturated-fat diet, but the activity remained 75% higher than in lean mice, whereas in obese mice pair-fed on the corn-oil diet the activity was the same as in lean mice. 7. During starvation the acyl-CoA desaturase activity in livers from obese mice decreased more slowly and proportionately less than in livers from lean mice. 8. It is concluded that increased substrate supply as a result of hyperphagia and not low concentration of linoleic acid is the main factor causing high acyl-CoA desaturase activity in obese mice.

The effect of dietary methyl branched-chain fatty acids on aspects of hepatic lipid metabolism in the rat

1. Rats were fed to appetite on a stock laboratory diet or on diets consisting of the stock diet and in addition 50 or 200 g triolein/kg, 50 g palmitic acid/kg or 50 g/kg of a concentrate mixture of methyl branched-chain fatty acids (Me-BCFA) which had been prepared from sheep adipose triacylglycerols. 2. No differences could be detected in the delta 9-desaturase activity or fatty acid synthetase activity of liver preparations from rats which had been fed on either the stock diet, the 50 g palmitic acid/kg or the 50 and 200 g triolein/kg diet; the palmitic acid diet was therefore taken as the control diet in subsequent experiments. 3. Rats consuming the 50 g Me-BCFA/kg diet exhibited a marked reduction in the capacity of their liver microsomes for delta 9-desaturation when compared with animals receiving the control diet. The delta 6-desaturase activity also showed an inhibitory trend with the Me-BCFA diet. 4. Microsomal omega-oxidation of fatty acids, mitochondrial succinate oxidation and the activity of cytosolic fatty acid synthetase (FAS) were unaffected by the ingestion of the Me-BCFA mixture compared with the diet which included palmitic acid. 5. There were no differences in the plasma concentration of thyroxin, insulin and glucagon between animals fed on the diets containing palmitic acid or the Me-BCFA. 6. For a given concentration of fatty acids the Me-BCFA had a greater inhibitory effect when added to incubations of liver microsomes from rats fed on the standard diet than did the addition of palmitic acid. 7. The observations in vivo and in vitro strongly suggested that the Me-BCFA were having a specific inhibitory effect on the desaturation reaction.

The influence of diet and diabetes on stearoyl Conenzyme A desaturase (EC 1.14.99.5) activity and fatty acid composition in rat tissues

1. Rats were given low-fat diets for 3 d in which the carbohydrate source was starch. The livers of animals given the fructose or sucrose had increased hepatic activities of the fatty acid synthetase and stearoyl CoA desaturase (EC 1.14.99.5) enzyme complexes: in those given fructose there was a lower activity of the enzymes in adipose tissue. 2. Similar results were obtained in rats given fructose diets for 30 d, but in animals which had previously been made diabetic with streptozotocin, the activities were lower. The dietary treatment made little difference to the fatty acid profiles of the tissue lipids. The diabetic condition on the other hand produced considerable changes in fatty acid profile. 3. With diets containing approximately 200 g fat/kg in the form of butter or of polyunsaturated margarine, the tissue lipids from rats given sucrose had less linoleic acid than those from rats given starch. In addition, there was the expected difference between the rats given butter or margarine. The results are discussed in relation to the current literature.