Biosynthesis of protein relative to the accumulation of fat in the liver of EFA deficient rats

Effect of an essential fatty acid (EFA) deficiency in the rat on the incorporation of leucine-¹⁴C and glucosamine-¹⁴C into serum and liver protein are reported. Weanling male rats of the Sprague-Dawley strain were raised on a fat-free diet for 10–12 weeks and then switched to diets supplemented with 10% corn oil or 10% hydrogenated coconut oil. Leucine-¹⁴C or glucosamine-¹⁴C was injected into the tail veins of the animals of each group. At selected intervals up to 120 min after the injections, the animals were sacrificed and the radioactivity of the liver and serum proteins was measured. The levels of triglyceride (TG) in the serum and the liver were also determined. Less radio-activity was incorporated into the serum β-lipoprotein (β-LP) fraction of the hydrogenated coconut oil than the corn oil fed animals injected with leucine-¹⁴C, but no differences were observed in the incorporation of radioactivity into the liver protein and both albumin and globulin fractions of the serum of these groups of animals. In the similar experiments with glucosamine-¹⁴C less radioactivity was incorporated into the β-LP fraction of the serum and into the smooth endoplasmic reticulum of the liver in the hydrogenated coconut oil (EFA deficient) than the corn oil fed animals. Time course studies also indicated that less radioactivity was incorporated into the β-LP fraction than into the albumin and globulin fractions of the serum of the hydrogenated coconut oil group. These findings suggest that an EFA deficiency results in an impairment of the synthesis or release of lipoprotein.     

Essential fatty acid-deficient rats: III. Distribution of lipid classes in rat testes after feeding partially hydrogenated oils

Total and relative amounts of neutral lipids (NL) and phospholipids (PL) as well as the distribution of various lipid classes in these were determined in testes of rats fed different types of partially hydrogenated oils for 5,15 and 26 weeks. The dietary fats were partially hydrogenated arachis oil (HAO), partially hydrogenated soybean oil (HSO), partially hydrogenated herring oil (HHO) and, for comparison, arachis oil (AO). An additional series of animals was reared on a fat-free diet throughout the entire experiment. The total amount of NL is decreased by EFA deficiency parallel with the development of the degenerative changes of the spermatogenic tissue. The relative amounts of NL in the testis are not influenced by EFA deficiency during the first stages of degeneration. However, feeding of HHO for 26 weeks resulted in a marked decrease in NL. The total content of PL is directly related to tissue degeneration. This observation is supported by the data obtained after 5 weeks of feeding HHO and by the correspondence between the results found after 15 and 26 weeks on HAO and the fat-free diets, respectively. The relative amount of PL is less influenced by EFA deficiency, but severe degenerations as found for the group fed HHO are followed by decreases. The neutral lipids had three main fractions: triglycerides (TG), free fatty acids (FFA) and cholesterol (Chol). FFA was found to be the main fraction of NL after 5 weeks, whereas TG was the main component of NL after 15 and 26 weeks, especially in the animals with degenerated testes. The presence of the large quantities of FFA is discussed. Cholesterol was decreased markedly in the EFA deficient rats fed partially hydrogenated oils, but not in the fat-free reared groups. The variations in the PL distribution during the experiment were small with regard to the two main PL classes, the phosphatidylcholines and the phosphatidylethanolamines. The most remarkable change among the PL classes was an increase in the percentage of sphingomyelins when the spermatogenic degenerations developed.     

Effects of dietarytrans acids on the biosynthesis of arachidonic acid in rat liver microsomes

Effects of dietarytrans acids on the interconversion of linoleic acid was studied using the liver microsomal fraction of rats fed a semipurified diet containing fat supplements of safflower oil (SAFF), hydrogenated coconut oil (HCO) at 5 and 20% levels or a 5% level of a supplement containing 50.3% linolelaidic and 24.3% elaidic acids devoid ofcis,cis-linoleic acid (TRANS). Growth rate was suppressed to a greater extent with the animals fed the 20% than the 5% level of the HCO-supplemented diets and still further by the TRANS diet compared to the groups fed the SAFF diets. Food intake was greater in the groups fed the HCO than the SAFF-supplemented diets, demonstrating the marked effect of an essential fatty acid (EFA) deficiency on feed efficiency. In contrast to an EFA deficiency produced by the HCO supplement, which stimulated the in vitro liver microsomal biosynthesis of arachidonic acid, diets containing the TRANS supplement exacerabated the EFA deficiency and depressed 6-desaturase activity of the liver microsomal fraction. The liver microsomal fraction of the animals receiving this supplement also was more sensitive to fatty acid inhibition of the desaturation of linoleic acid than those obtained from animals fed either the SAFF or HCO diets. It is suggested that dietarytrans acids alter the physical properties of the 6-desaturase enzyme system, suppressing its activity, which increases the saturation of the tissue lipids and, in turn, the requirement for EFA or polyunsaturated fatty acids.     

Efficacy of linoleic acid administered rectally as monoglyceride

The potential of the rectal route for administration of essential fatty acids (EFA) as monoglyceride (MG) was investigated. EFA-deficient rats were supplemented with 14 mg linoleic acid/day for 3 days. Supplementation was either by oral administration as corn oil, orally as corn oil-derived MG or rectally as MG. The patterns of polyunsaturated fatty acids (PUFA) in liver and serum lipids, characteristic of EFA deficiency, were altered in the direction of normalcy in similar magnitude by all modes of supplementation, indicating that the rectal route may be useful for administration of EFA. The amounts of phospholipids (PL) and free fatty acids (FFA) in liver changed by all modes of administration. The magnitude of change of total PL and of FFA in liver depended upon the chemical form in which linoleic acid was administered and the route of administration, indicating that these factors affect lipid metabolism.     

Increased liver lipase activity in rats with essential fatty acid deficiency

Liver lipase activity was measured in EFA-deficient rats (long-term) and in control rats and rats fed an EFA-deficient diet for two weeks (short-term). Liver lipase activity was significantly enhanced by EFA deficiency, both in long-term and short-term experiments. The enhanced liver lipase activity could be normalized by feeding these rats normal laboratory chow for 14 days. Since during EFA deficiency prostaglandin synthesis is impaired, the possible involvement of prostaglandins in the observed changes in liver lipase actvity during EFA deficiency was studied. Administration of the prostaglandin synthesis inhibitor indomethacin (5 mg/kg body weight, i.p.) to normally fed rats for two days led to an increase of liver lipase activity. Prostaglandin E₂ was found to inhibit the secretion of liver lipase activity by freshly isolated parenchymal liver cellsin vitro. These results indicate that the increase in liver lipase activity during EFA deficiency may be due to an impairment of the prostaglandin synthesis.     

Liver subcellular fatty acid profiles of chicks fed diets containing hydrogenated fats and varying linoleate levels

Day-old male broiler chickens were fed semipurified diets containing 5% lipid from one of four different lipid sources: corn oil (CO), partially hydrogenated soybean oil (HSBO), a spent restaurant grease (SRG) and a purified mixture of triolein, tripalmitin and tristearin (OPS). Diets CO and HSBO contained adequate amounts of linoleic acid, but diets SRG and OPS were deficient in linoleate. In addition, SRG and HSBO containedtrans isomers of 16∶1 and 18∶1. The diets were fed for 3 wk to determine the effects of low linoleate levels andtrans isomers on fatty acid profiles in liver microsomes, mitochondria and cytosol. Chicks fed HSBO had the highest body weights, while those fed SRG and OPS had the lowest. The incidence and severity of dermatitis were similar for all treatments. The proportions of linoleate and arachidonate in lipids from liver subcecullar fractions were reduced significantly in chicks fed OPS and SRG; however levels of 20∶3ω9 were not increased. Feeding HSBO, which is high in both linoleate and linolenate, resulted in higher levels of 18∶3ω3 and 20∶5ω3 in liver subcellular fractions and lower levels of 20∶4ω6 than those seen in chicks fed CO. The isomeric forms of 18∶1 present in the partially hydrogenated fats (HSBO and SRG) appeared to be incorporated into the lipids of liver fractions. The results of this study show that dietary lipids influence fatty acid, profiles of chick liver microsomes, mitochondria and cytosol. Decreases in linoleate and arachidonate in these organelles occur before overt essential fatty acid (EFA) deficiency signs in chicks fed EFA-deficient diets. Published as Scientific Paper No. 7512, College of Agriculture and Home Economics Research Center, Project No. 4723, Washington State University, Pullman, WA.     

Increased plasma triglyceride secretion in EFA-deficient rats fed diets with or without saturated fat

Metabolic responses to essential fatty acid-deficiency in rats include an increased rate of triglyceride secretion into the plasma, a large reduction in the HDL₁ plasma lipoprotein concentration, and increased concentrations of liver triacylglycerols and cholesteryl esters. Because of differences in the types of EFA-deficient diets used, it is not clear whether these responses were solely due to the absence of EFA from the diet or whether saturated fat, or differences in acyl group chain length in this fat, might be responsible. Therefore, we fed rats diets differing only in amounts and kinds of fat, and measured triacylglycerol secretion rates and liver concentrations of triacylglycerols and cholesteryl esters, for comparison with our earlier measurements of plasma high density lipoprotein subpopulations in rats fed exactly the same diets. The purified diets contained either no fat, 5% by weight hydrogenated coconut oil, 5% hydrogenated cottonseed oil, or each of these three diets supplemented with 1% safflower oil, or 5% corn oil. We also fed some rats a nonpurified stock diet for comparison with literature reports. The present results indicate that the metabolic responses to essential fatty acid deficiency described above are definitely due to essential fatty acid-deficiency and not to the presence or chain length of acyl groups in saturated fat in the diet. Presented in part at the May 1984 meeting of the American Oil Chemists' Society in Dallas, Texas.     

Effects of an essential fatty acid deficiency on serum lipoproteins in the rat

Studies are reported on the effect of an essential fatty acid (EFA) deficiency in male Sprague-Dawley rats and its exacerbation by inclusion oftrans fatty acids in the diet on the level and composition of serum lipoproteins. Weanling male Sprague-Dawley rats were fed diets containing all essential nutritients and a 5% fat supplement of safflower oil (SAFF) or hydrogenated coconut oil (HCO) in 2 experiments, one for 31 wk and the other for 17 wk. For the final 3 wk of each experiment, animals were switched from each group to a 5% supplement of a concentrate of ethyl linolelaidate (TRANS). In addition, a group of animals fed the HCO diet in the first experiment were also switched to the SAFF Diet. With the development of an EFA deficiency in the HCO group, there was a decrease in the high density lipoprotein (HDL) and an increase in the very low density plus the low density (VL-LDL) lipoprotein fractions separated by heparin-manganese precipitation. Switching animals of the HCO group to the TRANS supplement exaggerated this effect and produced a very low ratio of HDL-to-VL-LDL. Analysis of the serum lipoproteins by polyacrylamide disc gel electrophoresis showed that an EFA deficiency produced a marked alternation of the HDL fraction. Changes also appeared to be produced in the VL-LDL fraction by an EFA deficiency and particularly upon switching EFA-deficient animals to the TRANS supplemented diet. Switching animals of the SAFF group to the TRANS supplement brough about an immediate reduction in HDL with a corresponding decrease in serum arachidonic acid. The data suggested a general relationship between arachidonic acid and the level and composition of HDL on the one hand, and 18∶1 and VL-LDL on the other. Accordingly, the ratio of HDL-to-VL-LDL appears to provide a sensitive biochemical index of the EFA status of the rat.     

Effects of essential fatty acid deficiency on prostaglandin synthesis and fatty acid composition in rat renal medulla

Studies are reported on the capacity of isolated rat renal papilla (inner medulla) to synthesize and release prostaglandin (PG) E from endogenous and exogenous precursor(s) during development of an essential fatty acid (EFA) deficiency in the rat. Weanling (21-day-old) male Sprague-Dawley rats were fed a fat-free diet supplemented with either 5% hydrogenated coconut oil (HCO) or 5% safflower oil (SO). At approximately 3, 6 and 7 weeks (6, 9 and 10 weeks of age), groups of animals fed each diet were killed for studies of PGE synthesis in the renal papillae. Differences in the fatty acid composition of the papillae lipids of the animals of each group were also determined. The in vitro production of PGE from endogenous precursor(s) was significantly reduced in the papillae from the 6-week-old rats fed the HCO diet compared to the control (SO) rats, and appeared to be near maximally depressed in the 10-week-old animals compared to that of animals fed an EFA deficient diet for over a year in an accessory experiment. Analyses of the fatty acids of the papillae lipids of the HCO groups showed that the levels of 18∶2 and 20∶4 were markedly reduced, and those of 16∶1, 18∶1 and 20∶3 were elevated compared to the controls even in the 6-week-old animals, typical of an EFA deficiency. The papillae lipids of the animals fed the HCO diet were also depleted of their stores of 22∶4ω6. A fatty acid believed to be derived by chain elongation of 20∶3ω9, 22∶3, was found in large concentrations in the papillae triglycerides of the EFA deficient rats. Incubations of exogenous arachidonic acid (20∶4) in homogenates and tissue slices of the papillae of the HCO dietary groups showed that the PG synthetase was not impaired by an EFA deficiency. The rate of PGE synthesis in the papillae of the EFA deficient animals was generally enhanced when exogenous 20∶4 was added, indicating that the concentration of available precursor(s) is a primary factor in the control of PGE synthesis in the papilla of the rat.     

Metabolism of n−3 polyunsaturated fatty acids by the isolated perfused rat liver

The hepatic metabolism of oleic acid and n−3 fatty acids (eicosapentaenoic acid, EPA and docosahexaenoic acid, DHA), and secretion of very low density lipoprotein (VLDL) were studied in isolated perfused rat livers from normal chow fed male rats. The basal perfusion medium contained 30% bovine erythrocytes, 6% bovine serum albumin (BSA), and 100 mg/dL glucose, in Krebs-Henseleit bicarbonate buffer (pH 7.4) which was recycled through the liver for 2 hr. Individual fatty acids (EPA, DHA or oleic acid), as complexes with 6% BSA, or albumin alone, were infused at a rate of 70 μmol/hr. When any of these fatty acids was infused at this rate, the ambient concentration in the medium was maintained at 0.3–0.4 μmol/mL, indicative of similar hepatic rates of uptake for each fatty acid (i.e., approximately 6 μmol/g liver/hr). When fatty acid was not infused, the ambient free fatty acid level was 0.16 μmol/mL. The concentrations of infused free fatty acids increased appropriately in the perfusion medium; however, with infusion of EPA, DHA, or oleate, the concentrations of perfusate palmitate and linoleate were the same as when fatty acid was not infused. Additionally, the perfusate concentration of oleate in the free fatty acid fraction was not affected by infusion of EPA and DHA. These data indicate a constant outflow of endogenous fatty acid unaffected by the presence of the exogenously supplied fatty acid. The net secretion rate of VLDL lipids and protein was stimulated by infusion of oleate, whereas when EPA was infused, secretion rates were lower and similar [except for VLDL cholesterol (C), which was greater] to those occuring when fatty acid was not provided. DHA stimulated the secretion of VLDL triacylglycerol (TG), phospholipid (PL) and C to a similar rate, as did oleate, but secretion of VLDL cholesteryl ester (CE) and protein was lower and similar to that with EPA. VLDL and hepatic TG and CE were enriched with the infused fatty acids, compared to experiments without fatty acids, as determined by gas chromatography. Enrichment of PL, however, was significant only in liver upon infusion of EPA. The formation of¹⁴CO₂ and perchloric acid soluble products from [1-¹⁴C]EPA, considered separately, did not differ statistically from that obtained with [1-¹⁴C]oleate, although the mean values were higher with [1-¹⁴C]EPA. However, the sum of oxidation products derived from EPA was significantly greater than that from oleate. Incorporation of [1-¹⁴C]EPA into TG and CE, but not into PL, was lower as compared to that from [1-¹⁴C]oleate. These lower rates of incorporation of [1-¹⁴C]EPA into VLDL lipids therefore paralleled the mass fatty acid enrichment-patterns. It may be concluded that EPA is used to a similar extent as oleate for synthesis of PL, but is a poorer substrate for synthesis of TG. The reduced output of newly synthesized (radioactive) PL reflected the lower hepatic output of VLDL. Since hepatic uptake of EPA, DHA or oleate was identical, utilization of EPA for TG synthesis was less than that of oleate or DHA. Further-more, utilization of endogenous fatty acids for TG synthesis and secretion of the VLDL was reduced in the presence of EPA. The decreased TG synthesis resulted in reduced formation of VLDL for transport of TG from the liver. These effects taken together with an apparently increased oxidation of EPA provide substantial evidence for a decrease in formation of VLDL and transport of TG, PL, C and CE into the circulation in response to EPA. DHA, however, appears to be an adequate substrate for TG synthesis and stimulates VLDL secretion. The reduced transport of CE may reflect lower selectivity of DHA by acyl-CoA; cholesterol acyltransferase for CE formation.     

In vivo determination of triglyceride secretion using radioactive glycerol in rats fed different dietary saturated fats

Our objective was to determine the relative rates ofin vivo triglyceride (TG) secretion and the composition of very low density lipoproteins (VLDL) in rats fed different dietary saturated fats. Male Sprague-Dawley rats (150–200 g) were fed diets containing 16% corn oil, or 14% butterfat, 14% beef tallow, 14% olive oil, or 14% coconut oil plus 2% corn oil for 5 wk. Changes in plasma TG specific radioactivity were determined in individual, unanesthetized fasted rats after injection of 100 μCi [2-³H]glycerol. Nonlinear regression analysis using a 2-compartment model was used to determine the fractional rate constant for TG turnover in plasma. The plasma TG pool was 33–40% larger with beef tallow than with corn, olive or coconut oil feeding (p<0.05), and 20% larger with beef tallow than with butterfat feeding. The rate of TG secretion into plasma (mg/min/100 g body weight) was 60% higher in animals fed beef tallow than corn or coconut oil (p<0.05) and 26–33% higher in animals fed beef tallow than olive oil or butterfat. Differences in VLDL composition (% wt) were also noted. Our data suggest that greater TG secretion is the primary factor contributing to the larger TG pool with ingestion of beef tallow relative to butterfat, corn or coconut oil. These results suggest that different dietary saturated fats have unique effects on TG metabolism in rats. Presented in part at the 1990 meeting of the Federation of American Societies for Experimental Biology in Washington, D.C. (see ref. 1).     

Influence of medium-chain triglycerides on lipid metabolism in the rat

Lipid metabolism was studied in rats fed diets containing corn oil, coconut oil, or medium-chain triglyceride (MCT), a glyceride mixture containing fatty acids of 8 and 10 carbons in length. The ingestion of MCT-supplemented, cholesterolfree diets depressed plasma and liver total lipids and cholesterol as compared with corn oil-supplemented diets. In rats fed cholesterol-containing diets, plasma cholesterol levels were not influenced by dietary MCT, but liver cholesterol levels were significantly lower than in animals fed corn oil. In vitro cholesterol synthesis from acetate-1-¹⁴C was lower in liver slices of rats that consumed MCT than in similar preparations from corn oil-fed rats. Studies of fatty acid carboxyl labeling from acetate-1-¹⁴C and the conversion of palmitate-1-¹⁴C to C₁₈ acids by liver slices showed that chain-lengthening activity is greater in the liver tissue of rats fed MCT than in the liver of animals fed corn oil. The hepatic fatty acid desaturation mechanisms, evaluated by measuring the conversion of stearate-2-¹⁴C to oleate, was also enhanced by feeding MCT. Adipose tissue of rats fed MCT converts acetate-1-¹⁴C to fatty acids at a much faster rate than does tissue from animals fed corn oil. Evidence is presented to show that the enhanced incorporation of acetate into fatty acids by the adipose tissue of rats fed MCT represents de novo synthesis of fatty acids and not chain-lengthening activity. Data are also presented on the fatty acid composition of plasma, liver, and adipose tissue lipids of rats fed the different fats under study.     

Metabolism of erucic acid in perfused rat liver: Increased chain shortening after feeding partially hydrogenated marine oil and rapeseed oil

The metabolism of [14-¹⁴C] erucic acid was studied in perfused livers from rats fed on diets containing partially hydrogenated marine oil or rapeseed oil for three days or three weeks. Control rats were given groundnut oil. Chain-shortening of erucic acid, mainly to 18∶1, was found in all dietary groups. In the marine oil and rapeseed oil groups, the percentage of chain-shortened fatty acids in very low density lipoproteins-triacylglycerols (VLDL-TG) exported from the liver increased after prolonged feeding. A similar increase was found in liver TG only with partially hydrogenated marine oil. This oil, rich intrans fatty acids, thus seemed to be more effective in promoting chain-shortening. The fatty acid composition of the secreted and stored TG differed both with respect to total fatty acids and radioactively labeled fatty acids, indicating that at least 2 different pools of TG exist in the liver. The lack of lipidosis in livers from rats fed dietary oils rich in 22∶1 fatty acids is discussed in relation to these findings. In conclusion, a discussion is presented expressing the view that the reversal of the acute lipidosis in the hearts of rats fed rapeseed oil or partially hydrogenated marine oils is, to a large extent, derived from the increased chain-shortening capacity of erucic acid in liver.     

Dietary protein deficiency affects n−3 and n−6 polyunsaturated fatty acids hepatic storage and very low density lipoprotein transport in rats on different diets

Fatty livers and the similarity between the skin lesions in kwashiorkor and those described in experimental essential fatty acid (EFA) deficiency have led to the hypothesis that protein and EFA deficiencies may both occur in chronic malnutrition. The relationship between serum very low density lipoprotein (VLDL) and hepatic lipid composition was studied after 28 d of protein depletion to determine the interactions between dietary protein levels and EFA availability. Rats were fed purified diets containing 20 or 2% casein and 5% fat as either soybean oil rich in EFA, or salmon oil rich in eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, or hydrogenated coconut, oil poor in EFA. Animals were divided into six groups, SOC (20% casein +5% soybean oil), SOd (2% casein +5% soybean oil), COC (20% casein +5% hydrogenated coconut oil), COd (2% casein + 5% hydrogenated coconut oil), SAC (20% casein +5% salmon oil) and SAd (2% casein +5% salmon oil). After 28 d, liver steatosis and reduced VLDL-phospholipid contents (P<0.001) were observed in protein-deficient rats. In protein deficiency, triacylglycerol and phospholipid fatty acid compositions in both liver and VLDL showed a decreased polyunsaturated-to-saturated fatty acid ratio. This ratio was higher with the salmon oil diets and lower with the hydrogenated coconut oil diets. Furthermore, independent of the oil in the diet, protein deficiency decreased linoleic and arachidonic acids in VLDL phospholipids. Conversely, despite decreased proportions of EPA at low protein levels, DHA levels remained higher in rats fed salmon oil diets. While in rats fed the hydrogenated coconut oil-fed diets the amount of 22∶5n−6 was lower in liver, it was higher in VLDL lipids at low protein levels. Both EPA and arachidonic acid are precursors of eicosanoids and their diminution may be related to certain clinical symptoms seen in infants suffering from kwashiorkor.     

Effect of essential fatty acid deficiency on lipid metabolism in isolated fat cells of epididymal fat pads of rats

Lipogenesis, lipolysis, and stimulation of glucose conversion into lipid by insulin or prostaglandin E₁ were studied in isolated fat cells of the epididymal fat pads of rats fed a fat-free diet or this diet supplemented with 10% hydrogenated coconut oil or 10% safflower seed oil. Changes in fatty acid composition, characteristic of an essential fatty acid deficiency, were well advanced in the neutral lipid but had only started in the polar lipid of the fat cells of the epididymal fat pads of animals 3 months after weaning. Cellularity of the epididymal fat pads, as indicated by protein to lipid ratio of the fat cells, was influenced greatly by hydrogenated coconut oil in the diet irrespective of an essential fatty acid deficiency. Lipogenesis was increased in the fat cells of the animals fed the hydrogenated coconut oil diet 5 weeks after weaning but was not significantly different from that of the safflower fed animals 3 months after weaning. Incorporation of glucose into lipid, oxidation to CO₂, and basal lipolysis were not significantly different in the fat cells of the essential fatty acid deficient animals from those fed safflower oil 3 months after weaning, except in animals of the fat-free group based upon cell lipid. However, conversion of glucose to free fatty acid was significantly greater in the isolated fat cells of animals fed either the hydrogenated coconut oil or the fat-free diet than in those of animals fed the safflower oil supplement. The incorporation of glucose into lipid by isolated fat cells was stimulated significantly by insulin in young animals fed a fat-free diet, but the effect on lipogenesis appeared to be reversed in the fat cells of animals receiving safflower seed oil 3 months after weaning. Prostaglandin E₁ also appeared to stimulate the incorporation of glucose into lipid in the fat cells of the older animals receiving safflower seed oil. Differences in osmolarity produced large differences in utilization of glucose and release of lipid from isolated fat cells, but no significant differences were observed between the cells from animals fed the fat-free diet and those from the controls fed safflower oil. The results demonstrated the effects of diets containing fat or no fat on enzyme activities and membrane properties of fat cells of the epididymal fat pads of essential fatty acid deficient rats.     

Synthesis of cholesterol and total lipid by male and female rats fed beef tallow or corn oil

Male and female weanling rats were fed diets containing 2 or 42% of calories as corn oil or 40% as beef tallow plus 2% as corn oil until they were 12 or 18 weeks of age. Incorporation of C¹⁴-acetate into lipids of serum and liver and concentration of lipids in serum, liver, and carcass at the end of these periods were determined. Net synthesis of noncholesterol lipid was repressed by changing the diet from 2% to 42% of calories from either dietary fat in both sexes and at both ages. Cholesterol net synthesis was enhanced 29-fold in males and 22-fold in females fed 42% corn oil compared to 2% corn oil to the age of 12 weeks. It was enhanced only 2.6-fold for males and 3.4-fold for females by 40% beef tallow plus 2% corn oil. At 18 weeks of age cholesterol synthesis in males fed 42% corn oil was 7.3 and in females 9.1 times the value for those fed 2% corn oil. At this age the values for rats fed 40% beef tallow plus 2% corn oil were 1.2 and 3.7 times those for 2% corn oil fed rats of the respective sexes.     

Stearoyl-CoA desaturase activity in mammary adenocarcinomas carried by C3H mice

Transplantable mammary adenocarcinomas and livers of C3H mice fed a stock diet or a linoleate rich diet (15% corn oil) contain similar amounts of oleate (ca 3 mg/gm tissue). On feeding either a high carbohydrate, fat free or a high carbohydrate, saturated fat-containing (15% hydrogenated coconut or cottonseed oil) diet for 6 weeks, oleate levels increased 2-fold in tumor and 5-fold in liver. The specific activity of stearoyl-CoA desaturase in liver microsomes was similar to that in the corresponding fractions of mammary glands of lactating mice. In liver, this activity was enhanced 2- to 3-fold by feeding a high carbohydrate, fat free or a high carbohydrate, saturated fat diet. The desaturase activity in mammary tumor microsomes, while only 10% of that in hepatic microsomes, remained unaltered regardless of the type of diet fed. These observations suggest that (a) a major portion of the oleate in the mammary tumor is not produced within the tissue, (b) dietary adaptation is not a general characteristic of stearoyl-CoA desaturase in neoplastic tissues, and (c) enhanced desaturase activity in liver is directly related to the absence of linoleate or oleate, or to a large decrease in oleate in the diet.     

Specific inhibition of hepatic fatty acid synthesis exerted by dietary linoleate and linolenate in essential fatty acid adequate rats

Dietary linoleate and linolenate were investigated for their ability to specifically inhibit liver and adipose tissue lipogenesis in meal-fed (access to food 900-1,200 hr), essential fatty acid (EFA) adequate rats. Supplementing a high carbohydrate diet containing 2.5% safflower oil with 3% palmitate 16∶0, oleate 18∶1, or linoleate 18∶2 did not affect in vivo liver or adipose tissue fatty acid synthesis. However, 18∶2 addition to the basal diet did result in a significant (P<0.05) decline of liver fatty acid synthetase (FAS) and glucose-6-phosphate dehydrogenase (G6PD) activities. When the safflower oil content of the basal diet was reduced to 1%, the addition of 3% 18∶2 or linolenate 18∶3 significantly (P<0.05) depressed hepatic FAS, G6PD, and in vivo fatty acid synthesis by 50%. Addition of 18∶1 caused no depression in hepatic FAS activity but did result in a significant (P<0.05) decline in liver G6PD activity and fatty acid synthesis which was intermediate between basal and basal +18∶2-or+18∶3-fed animals. Adipose tissue rates of lipogenesis were completely unaffected by dietary fatty acid supplementation. Similarly, the addition of 3 or 5% 18∶3 to a basal diet for only one meal resulted in no change in lipogenesis relative to that in animals fed the basal diet. The data indicate that, like rats fed EFA-deficient diets, dietary 18∶2 and 18∶3 exert a specific capacity to depress rat liver FAS and G6PD activities and rate of fatty acid synthesis. Michigan Agricultural Experiment station Journal Article No. 7581. D.R. Romsos is the recipient of Career Development Award K04 AM 00112     

Effect of essential fatty acid deficiency on myelin proteins

The effect of essential fatty acid (EFA) deficiency on rat-brain myelin proteins was studied. Rats were maintained on a lipid-free diet and compared with control rats fed the same diet supplemented with 3% corn oil. At 17 days of age, each pup was injected with [³H]leucine and rats from each group were killed over a period of 163 days. Although a large decrease occurred in the total amount of myelin protein per brain, the proportions of constituent myelin proteins remained relatively unchanged. Metabolic studies showed a decrease in the net turnover of myelin proteins analogous to that previously demonstrated for myelin phospholipid (PL).     

Influence of dietary fat on metabolism of (14-14C)erucic acid in the perfused rat liver. Distribution of metabolites in lipid classes

Two groups of rats were fed diets containing 20% by weight of either partially hydrogenated marine oil supplemented with sunflower seed oil (PHMO) or palm oil (PO) for 8 wk. Using a liver perfusion system, the effect of dietary long chain monoenoic fatty acids on the uptake and metabolism of [14-¹⁴C]erucic acid was studied. The perfusion times were 15 and 60 min, respectively. The two groups showed equal ability for erucic acid uptake in the liver but differed in the channeling of the fatty acids into various metabolic pathways. A higher metabolic turnover of 22∶1 in the PHMO livers relative to the PO livers was demonstrated by an increased recovery of total [¹⁴C]labeling in the triglyceride (TG) and phospholipid (PL) fractions, already evident after 15 min of perfusion. The chainshortening capacity was highest in the PHMO group, reflected by a higher [¹⁴C]18∶1 incorporation in both TG and PL, and increasing from 15 to 60 min of perfusion. The amount of [¹⁴C]18∶1 found in PL and TG after 60 min of perfusion of livers from rats fed PO corresponded to that shown for the PHMO group after 15 min. The PL demonstrated a discrimination against 22∶1 compared to TG, and, when available, 18∶1 was highly preferred for PL-synthesis. The total fatty acid distribution in the TG, as determined by gas liquid chromatography (GLC), reflected the composition of the dietary fats. In the total liver PL, 22∶1 and 20∶1 were present in negligible amounts, although the PHMO diet contained 12–13% of both 22∶1 and 20∶1. In the free fatty acid fraction (FFA), the major part of the radioactivity (≈80%) was [14-¹⁴C]erucic acid, and only small amounts of [¹⁴C]18∶1(<2%) were presents, even after 60 min of perfusion. The shortened-chain 18∶1 was readily removed from the FFA pool and preferentially used for lipid esterification.