Animal endogenous triglycerides: II. Rat and chicken adipose tissue

The endogenous adipose tissue triglycerides of rat and chicken differ markedly in composition from those of swine although all three contain the same major fatty acids. The main difference is that the swine triglycerides have saturated fatty acids in the middle position, whereas in rat and chicken that position is preferentially occupied by unsaturated acids. In swine adipose tissue triglycerides the order of preference for the middle position is 16∶0>16∶1>18∶0>18∶1, whereas in rat and chicken triglycerides the order is 18∶1>16∶1>18∶0>16∶0. Generalizing, in swine the order of preference for the 2 position is chain length over unsaturation, shorter chains over longer chains, and saturation over unsaturation. In rat and chicken, the degree of unsaturation prevails over chain length, longer chains over shorter chains, and unsaturation over saturation.     

Animal endogenous triglycerides: I. Swine adipose tissue

The objective of this study was to define the composition of endogenous glycerides of swine adipose tissues as a basis for further studies on the influences of diet and other environmental factors. It was also hoped that the endogenous triglyceride composition might suggest a fresh approach to the problem of the biosynthetic pathway of natural triglyceride mixtures. Swine were fed a fat-free diet from the age of 17 days to 5 months, and the triglycerides of their mesenteric, perirenal and inner and outer back adipose tissues analyzed by silver ion thin layer chromatography and gas liquid chromatography. Four silver ion fractions were found, S₃, S₂M, SM₂ and M₃ (S, saturated; M, monounsaturated fatty acids). Corresponding fractions from different adipose tissues had identical fatty acid composition. The fatty acid compositions of the 2 position of the fractions were also identical. However, the fatty acid composition of the unfractionated triglycerides varied from tissue to tissue. It is concluded therefore, that the various adipose tissues of swine contain the same triglycerides in varying concentrations. Stearic and oleic acids were located mainly in the combined 1 and 3 positions. Myristic, palmitoleic and palmitic were in the 2 position, with almost 90% of the saturated acids being palmitic. This specific distribution of the major fatty acids can explain the marked simplicity of swine endogenous triglycerides.     

Fatty acid composition of tissue lipids from miniature swine: Influence of dietary sucrose and starch

The fatty acid composition of serum, liver and adipose tissue from Pitman-Moore miniature swine was determined following their consumption of starch- or sucrose-containing diets for a period of one year. Among the tissues studied there were no significant differences in the fatty acid composition due to the type of dietary carbohydrate (starch or sucrose). The cholesteryl ester fatty acid composition of all samples studied remained quite constant. There were minor fluctuations in fatty acid composition of phospholipids and triglycerides from serum collected at diferent intervals following initiation of the diets.     

Lipid metabolism in plasma,liver, and adipose tissue of rats with experimental chronic nephrotic syndrome

Plasma, liver, and adipose tissue lipid composition and synthesis from [1-¹⁴C] acetate were studied three months following induction of nephrotic syndrome in rats by injection of antiglomerular basement membrane protein. Plasma triglyceride concentrations and specific radioactivities were elevated, and the triglycerides contained increased proportions of oleic acid. Plasma cholesterol and phospholipid concentrations were also increased, but free fatty acid levels were not. Liver triglyceride concentrations were decreased and incorporation of [1-¹⁴] acetate into liver triglycerides was also depressed below that of normal controls. Nephrotic rat liver triglycerides contained a higher proportion of oleic acid and lower arachidonic acid than did controls. Incorporation of [1-¹⁴C] acetate into adipose tissue lipids of the nephrotic rats was increased, and the proportion of palmitic acid was decreased. In the chronic nephrotic rat, the major source of the increased plasma triglycerides may be fatty acids mobilized from adipose tissue stores.     

Fatty acid turnover rates in the adipose tissues of the growing chicken (Gallus domesticus)

The purpose of this study was to investigate the mobility of fatty acids in adipose tissue of the chicken and to determine whether adipose tissue dynamics are altered by dietary repartitioning agents. To this end, the turnover rates of fatty acids and triglycerides were estimated in adipose tissue of growing chicks by using isopentadecanoic acid (IPDA) and elaidic acid (EA) as marker dietary fatty acids. The half-life of IPDA in abdominal and sartorial adipose tissues of birds over 6 to 10 wk of age were 20±4 and 23±6 d, respectively. The half-life for the remaining total carcass lipids was 23±3 d. The corresponding half-life for EA in abdominal fat tissue of birds over 2 to 7 wk of age was 18±3 d, a half-life not significantly different from the IPDA half-lives. On the other hand, a thyromimetic repartitioning agent (L-94901) fed to birds at the 2 ppm level from 2 to 7 wk of age significantly decreased the half-life of EA in abdominal fat tissue to 6±2 d. The data suggest that fatty acids were released from a more labile adipose site and subsequently reincorporated into abdominal and sartorial tissues and that fat mobilization occurred at the same time as did adipose tissue deposition in the growing chicken. Presented in part at the XVIII World Poultry Congress, Nagoya, Japan, September 1988. Reference to a brand or firm name does not constitute an endorsement by the U.S. Department of Agriculture over others of a similar nature not mentioned.     

Cholesterol and fatty acid synthesis in swine

In incubation studies with swine tissue slices, acetate-1-¹⁴C or glucose-U-¹⁴C as substrates were incorporated more readily into fatty acids and cholesterol in adipose tissue than other tissues tested. Cholesterol and fatty acid synthesizing activity was substantial in the small intestine. When acetate was available, liver, small intestine, and adipose tissue were important sites for cholesterol synthesis. Heart and aortic tissue had marginal levels of cholesterol synthesizing ability. Lipogenesis in adult swine liver, heart, and aortic tissue was extremely low. As in tissue slices, incorporation of acetyl-1-¹⁴C CoA into fatty acids by adipose homogenates indicated high lipogenic activity. Subcellular fractionations of heart and aortic tissue indicated that the heart microsomal fraction had the highest lipogenic activity as measured by the incorporation of acetyl-1-¹⁴C CoA into fatty acids. In adult swine adipose tissue, the incorporation of glucose-U-¹⁴C into fatty acid was higher than its incorporation into glyceride-glycerol. The synthesis of glyceride-glycerol from glucose-U-¹⁴C or acetate-1-¹⁴C in liver was higher than for fatty acid synthesis. The activity of acetyl CoA carboxylase, fatty acid synthetase, citrate cleavage enzyme, nicotinamide adenine dinucleotide phosphate-malate dehydrogenase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase was considerably higher in adipose tissue than in other tissues tested, paralleling its high lipogenic capacity. A preliminary report of this paper was given at the AOCS 66th Annual Spring Meeting, Dallas, Texas, April 30, 1975, Abstr. No. 109. In partial fulfillment of the requirement for the PhD degree in Nutritional Sciences at the University of Illinois at Urbana-Champaign.     

Effect of dietary fat supplementation on the composition and positional distribution of fatty acids in ruminant and porcine glycerides

Dietary fats which were protected from ruminal metabolism were fed to ruminants, and the constituent fatty acids subsequently appeared in the glycerides of tissues and secretory products. These dietary fat induced alterations in tissue lipid composition were particularly apparent when the fat source was enriched with linoleic acid. Similarly, when pigs were fed linoleic-enriched fats, the linoleic acid was incorporated into the adipose tissue triglycerides. Stereospecific analyses were carried out on triglycerides from various tissues and secretory products obtained from animals fed control or linoleate-enriched diets. The analysis of adipose tissue triglycerides showed that linoleate and oleate were preferentially esterified to positions 2 and 3 (cattle and sheep), and positions 1 and 3 (pigs). Of the other major adipose tissue fatty acids, palmitate was preferentially esterified at position 1 (ruminants) and position 2 (pigs), and stearate was preferentially esterified at positions 1 and 3 (ruminants), and position 1 (pigs). Stereospecific analysis of high mol wt milk triglycerides showed that linoleate was either evenly distributed on all three positions (goats), or predominantly on position 3 (cows). Furthermore, the incorporation of this linoleate did not markedly alter the positional specificity of the other major milk triglyceride fatty acids. Of these fatty acids, the short and medium chain length acids (butyratelaurate) were mainly on position 3, myristate and palmitate on positions 1 and 2, and stearate and oleate evenly distributed. Thoracic duct lymph triglycerides from sheep tended to show preferential incorporation of linoleate at position 3, palmitate at position 2, and stearate at position 1 and 3; oleate, on the other hand, tended to be evenly distributed on all three positions of the lymph triglyceride. The stereospecific arrangement of fatty acids in sheep liver triglycerides was similar to that of lymph triglycerides, and this may reflect the uptake of intact or partially hydrolysed chylomicron and/or very low density lipoprotein triglycerides by the liver. There were also some analogies in the stereospecific arrangement of fatty acids on ruminant lymph and milk triglycerides and this may reflect an incomplete hydrolysis of chylomicron and/or very low density lipoprotein triglycerides prior to uptake by the mammary gland. An unusual feature of lymph from sheep fed linoleate was the presence of phospholipids which contained large amounts of linoleate in ca. equal proportion at both positions 1 and 2 of the phospholipid molecule.     

Quantitative effects of dietary polyunsaturated fats on the composition of fatty acids in rat tissues

A method combining data on fatty acid composition into subsets is used to illustrate general relative competitive selectivities in the metabolic and transport events that maintain fatty acid compositions in tissue lipids and to minimize differences among tissues or species in the amount of individual fatty acids. Fatty acid compositions of triglycerides and phospholipids in several tissues of the rat were maintained with simple relationships between the exogenous n−3 and n−6 dietary polyunsaturated fatty acids and the endogenous n−7 and n−9 types of fatty acid. The general pattern of fatty acids in triglycerides was similar for liver, plasma and adipose tissue, averaging about 30% as saturated acids, 67% as 16- and 18-carbon unsaturated acids and only about 2% as 20- and 22-carbon highly unsaturated acids. The tissues maintained a linear relationship between the amount of 18-carbon polyunsaturated fatty acids in the diet and in the tissue triglycerides, with the proportionality constant for 18∶3n−3 being 60% of that for 18∶2n−6. The total phospholipids of liver, plasma and red blood cells maintained about 45% of the fatty acids in the form of saturated fatty acids and 20–30% as 20- and 22-carbon highly unsaturated fatty acids irrespective of very different proportions of n−3, n−6 and n−9 types of fatty acids. In all three tissues, the 20-carbon highly unsaturated fatty acids of the n−3, n−6 and n−9 type were maintained in a competitive hyperbolic relationship with apparent EC₅₀ values for dietary 18∶2n−6 and 18∶3n−3 near 0.1% of dietary calories. The consistent quantitative relationships described in this study illustrate an underlying principle of competition among fatty acids for a limited number of esterification sites. This approach may be useful in predicting the influence of diet upon tissue levels of the substrates and antagonists of eicosanoid biosynthesis.     

Effect of dietary saturated fatty acids and linoleic acid upon the structures of triglycerides in rabbit tissues

Five groups of rabbits were given a diet supplemented with safflower seed oil and safflower seed oil partially replaced by lauric, myristic, palmitic, and stearic acids respectively. After 10 weeks, plasma samples were taken from the animals in the fasted and nonfasted state; the animals then were killed, and the livers and samples of adipose tissue were removed. Lipids were extracted from the tissues, then separated into classes; and the fatty acid composition of each class was determined. In addition, the triglycerides were isolated and the structures determined by stereospecific analysis. There were marked differences in the compositions and structures of the triglycerides in the plasma from fasted and nonfasted animals. Feeding specific dietary fatty acids also greatly changed the metabolism of linoleic acid by the animals. The results are discussed in terms of the biosynthesis of triglycerides in plasma, liver, and adipose tissue.     

Esterification of fatty acids by bovine intramuscular and subcutaneous adipose tissues

Exogenous fatty acid esterification in intramuscular and subcutaneous adipose tissues from 72-hr fasted orad libitum fed Angus cattle was investigated. Intramuscular (interfascicular) and subcutaneous adipose tissue snips were obtained from the longissimus dorsi muscle and were incubated with radioisotopically labeled fatty acids (palmitate, stearate, oleate, linoleate or linolenate) at three different concentrations (0.3 mM, 0.6 mM and 2.0 mM) to assess rates of fatty acid incorporation into glycerolipids. Rates of fatty acid esterificationin vitro increased with fatty acid concentration in both intramuscular and subcutaneous adipose tissues. For all of the fatty acids investigated, triglycerides were the predominant products (60–85%). Subcutaneous adipose tissue had larger adipocytes and more actively (P<0.05) esterified fatty acids, with the exception of palmitate, than intramuscular adipose tissue. The rate of palmitate esterification was not different between tissues, although intramuscular adipose tissue esterified a greater proportion (P<0.10) of palmitate as triglyceride (85%) than did subcutaneous adipose tissue (75%). Relative rates of incorporation of fatty acids into lipids in intramuscular and subcutaneous adipose tissues were: palmitate > linolenate > linoleate > stearate. In general, 72-hr fasting did not significantly reduce the rates of fatty acid incorporation in bovine adipose tissues. Results of this study revealed that: i) rates of exogenous fatty acid incorporation into adipose tissue lipids were dependent on the medium fatty acid concentration and adipose tissue depot; and ii) the relative esterification rates of the various fatty acidsin vitro did not necessarily reflect the proportion of these fatty acids in bovine adipose tissues. Published as technical article 24910, Texas Agricultural Experiment Station.     

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

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

The structures of triglycerides from atherosclerotic plaques and other human tissues

Stereospecific analysis of trigly cerides isolated from human liver showed that these were much more asymmetric than the triglycerides from human adipose tissue. Heart muscle triglycerides were similar in structure to adipose tissue triglycerides. The triglycerides from aortic plaques were intermediate in structure between triglycerides of liver and adipose tissue.     

Drugs and Lipid transport

Drugs such as ethanol, carbon tetrachloride, ethionine or ACTH have a profound influence on lipid metabolism. The enzymatic synthesis of triglycerides and phospholipids by the liver, the release of triglycerides from liver to plasma and the transport of free fatty acids from adipose tissue are affected. These changes in lipid metabolism may be considered as resulting from chemically induced stress. In order to study the transport of lipids during a stress not induced by drugs, cold stress was also investigated. The changes in lipid transport following ethanol or ACTH administration were quite different from those observed during cold stress where body temp must be maintained by mobilization of energy producing substrates. However, the alterations in lipid transport during both cold and drug induced stress are dependent on the sex of the rat. The observed effects apparently involve a sexdependent transport of triglycerides from liver to plasma and also a sex-dependent mobilization of energy-producing substrates.     

Dietary fatty acids: Their metabolic fate and influence on fatty acid biosynthesis

Adult rats fed a low-fat diet or diets containing 15% of either tripalmitin, triolein or trilinolein were injected intraperitoneally with H³-labeled acetate. Those which received fat were also given by mouth, simultaneously with acetate, the 1-C¹⁴-labeled sodium salt of the respective dietary fatty acid. The fate of the tagged material was followed by time-spaced biopsies of subcutaneous adipose tissue and by collection of the expired C¹⁴O₂. After 72 hr, 51, 64, and 52% of the dietary palmitate, oleate, and linoleate, respectively, were catabolized, as indicated by the corresponding percentages of the label having been excreted as C¹⁴O₂. Dietary linoleate was relatively less incorporated into body triglycerides than palmitate and oleate. Animals ingesting diets of 15% triolein had only about one-half the amount of phospholipids in their tissues as had the other groups. The distribution of both the C¹⁴ and H³ labels in the tissue triglycerides showed that all diets containing fats decreased fatty acid synthesis but did not inhibit conversion of palmitate to oleate. Conversions of oleate or linoleate appeared to be through acetate. As a result of these factors, the fatty acid composition of the tissue triglycerides after 3 months’ ingestion of tripalmitin was essentially the same as that of the low-fat group, whereas the ingestion of triolein produced triglycerides with a very high content of oleic acid. Trilinolein ingestion produced effects similar to triolein but to a less pronounced degree. Both the respiratory C¹⁴O₂ and the C¹⁴- and H³-labeled fatty acids in subcutaneous adipose tissue exhibited a second rise in specific activity 12 to 24 hours after the administration of the label. Presented at the AOCS meeting, Chicago, 1964.     

Lipids and lipogenic enzymes in adipose tissue of castrated male goats

Male goats (“Criolla Argentina” breed), castrated at 45 days of age, showed altered lipid metabolism 180 days after castration as compared to control goats. Subcutaneous, perirenal and omental adipose tissues of castrated goats showed increases in fatty acid synthetase, glucose-6-phosphate dehydrogenase and NADP-isocitrate dehydrogenase activities. Castration increased the amount of total lipids and triglycerides, but did not modify the amount of cholesterol, phospholipid and protein in the three types of adipose tissue. The incorporation of [1-¹⁴C]acetate into fatty acids of subcutaneous and perirenal adipose tissue was increased in castrated goats in relation to noncastrated goats. Our results suggest that removal of gonadal steroids increases significantly the rate of lipogenesis in adipose tissue of male goats.     

A gas chromatography‐mass spectrometry method for the detection of adipocere in grave soils

Adipocere refers to a decomposition product, which forms due to the post‐mortem conversion of adipose tissue into a lipid mixture. During the conversion process, triglycerides present in the adipose tissue convert to free fatty acids via hydrolysis. Under the right conditions, hydrogenation of the free fatty acids will yield adipocere, which is chiefly comprised of saturated fatty acids. In a burial environment, adipocere may form macroscopically on the decomposing remains, but may also leach into the surrounding soil. This paper describes the development of a gas chromatography‐mass spectrometry method which allows for the quantitative analysis of trace levels of adipocere in grave soils.     

Triglyceride sub-classes of various dog adipose tissue sites

Lipids were extracted from four dog adipose tissue sites, perirenal, pericardial, inguinal subcutaneous, and mesenteric. The triglycerides were purified by thin-layer chromatography and the sub-classes separated by silver nitrate-silica gel plates. Gas chromatography was used to delineate the fatty acid composition of each subclass. The major sub-class was 011, followed by 012, 001, 111 and 112 in that order (0=saturated fatty acid; 1=one double bond; 2=two double bonds). The other components were present in minor amounts. The pericardial triglyceride had more 012 while the perirenal adipose tissue contained less 011 and more 001 than other sites. The other sub-classes were essentially similar. The distribution, based on 100%, of each saturated fatty acid was not the same in all sub-classes, although the over-all average was similar in each site. Presented at the AOCS Fall Meeting, Philadelphia, 1966.     

Adipose hormone-sensitive lipase preferentially releases polyunsaturated fatty acids from triglycerides

Rat adipose hormone-sensitive lipase-mediated release of fatty acids from triglycerides was studied in three model systems: i) cultured preadipocytes containing polyunsaturated fatty acid-enriched triglyceride; ii) perfused epididymal fat pads; and iii)in vitro incubations of crude preparations of hormone-sensitive lipase with synthetic triglyceride-analogues as substrates. We found that cultured preadipocytes challenged with 10μM norepinephrine tended to release more ω6 and ω3 polyunsaturated fatty acids than saturated fatty acids. Fat pads perfused with 10 μM norepinephrine preferentially released arachidonate and α-linolenate but tended to retain oleate and linoleate. Finally, crude preparations of hormonesensitive lipase released from the triglyceride-analogue substrates α-linolenate twice as fast as oleate. We conclude that rat adipose hormone-sensitive lipase preferentially releases polyunsaturated fatty acids from triglycerides. We suggest that this may be a mechanism by which these fatty acids are kept from being trapped in fat depots and maintained in the circulation.     

The structures of the principal glycerolipids of pig liver

The lipid composition of pig liver has been determined. The principal glycerolipids, i.e., triglycerides, phosphatdyl choline, phosphatidyl ethanolamine and phosphatidyl inositol, were isolated and the positional distribution of fatty acids in each determined by stereospecific analysis procedures. Previous results for the triglycerides were confirmed, while the phospholipids were similar in structure to those found in most other animal livers. The triglycerides were separated into simpler molecular species by combinations of silver nitrate thin layer chromatography and high temperature gas liquid chromatography, but the proportions found did not agree well with those calculated assuming a 1-random, 2-random, 3-random arrangement. The phospholipids were hydrolyzed with phospholipase C and converted to diglyceride acetates that were fractionated into simpler molecular species by the same procedures as were used with triglycerides. Highly specific fatty acid combinations were found in molecular species, and these specificities were very similar to those reported in similar lipids from the livers of such disparate species as the rat and chicken.     

Effect of lactation on lipolysis in rat adipose tissue

The concentrations of nonesterified fatty acids and glycerol in rat parametrial adipose tissue increased at peak lactation. Adipose tissue from lactating rats showed higher rates of release of nonesterified fatty acids and glycerol when incubated in vitro than did tissue from nonlactating rats, but there was a substantial increase in the esterification of fatty acids during involution. These results support earlier evidence that fat reserves were mobilized during lactation.