The incorporation of14C-glycerol into different species of diglycerides and triglycerides in rat liver slices

The relative rates of de novo synthesis of species of diglycerides and triglycerides from¹⁴C-glycerol were examined in rat liver slices. Diglycerides containing one or two double bonds per molecule and triglycerides containing four or more double bonds per molecule represented 70% and 60% respectively of the newly synthesized diglycerides and triglycerides. The newly synthesized triglycerides were more unsaturated than the endogenous triglycerides. Our results suggest that a nonrandom synthesis of species of diglycerides occurred followed by an almost random utilization of the various diglyceride species for the biosynthesis of triglycerides.     

The structure of triglycerides in selected oils containing erucic acid

The fatty acid compositions of 7 oils containing different amounts of erucic acid (1.4 to 57.2%) have been investigated. Fatty acid distribution between the 1,3- and 2-positions of the glyceride molecules was estimated by the pancreatic lipase splitting technique. On the basis of this experimental data, it is possible to speculate on the rules governing glyceride composition in the oils investigated. Presented at the AOCS Meeting in Houston, April 1965 Part of the T.P. Hilditch Symposium on Analysis of Natural Fat Triglycerides (JAOCS, September through December, 1965).     

Incorporation ofcis-octadecenoic acids into the rat liver mitochondrial membrane phospholipids and adipose tissue triglycerides

The incorporation of the dietarycis 18∶1 (n−12) andcis 18∶1 (n−10) into liver mitochondrial membrane phospholipids and adipose tissue trigly cerides was studied in 4 groups of rats fed diets containing 10 weight percent (wt%) of fat with the following contents of octadecenoic acids: 50%cis 18∶1(n−12) +9%cis 18∶1 (n−9); 25%cis 18∶1 (n−12)+32%cis 18∶1 (n−9); 50%cis 18∶1 (n−10)+10%cis 18∶1 (n−9); or 54%cis 18∶1 (n−9). Dietary linoleic acid was 3 wt% in all 4 groups. In the mitochondrial membranes, the isomeric octadecenoic acids were primarily incorporated into the 1-position of phosphatidylcholines and phosphatidylethanolamines at the expense of saturated fatty acids. The maximal incorporations observed in the 1-position of phosphatidylethanolamines were 4.8% 18∶1 (n−12) and 8.9% 18∶1 (n−10). No effects on the contents of polyunsaturated fatty acids in the phospholipids were seen. In the adipose tissue, the isomeric octadecenoic acids were incorporated at a level of 13%cis 18∶1 (n−12) or 23%cis 18∶1 (n−10), paralleled by a reduction in the content of oleic acid. Presented in part at the 9th Scandinavian Symposium on Lipids, Visby, Sweden, June 1977.     

Stereospecific analysis of hepatoma,host liver,and normal rat liver triglycerides from animals on chow and fat free diets

Triglycerides from normal liver, host liver, and hepatoma of rats maintained on chow and fat-free diets were subjected to stereospecific analysis. Normal and host liver triglycerides from animals on the same diet did not exhibit significant differences. Fat-free diet reduced polyunsaturated fatty acids in normal and host liver triglycerides, but had no effect upon hepatoma triglycerides. Each position of hepatoma and liver triglyceride glycerol exhibited a characteristic fatty acid composition. Palmitate concentrations were reduced dramatically and stearate levels were increased significantly at the 1 position of hepatoma triglycerides, relative to the corresponding position of liver triglycerides which were affected little by diet or tumor. Except for higher percentages of C-20 and higher fatty acids, common to all three positions, the composition of hepatoma triglycerides at the 2 position appeared normal. The 3 position of hepatoma triglycerides contained significantly higher percentages of stearate than liver. Data obtained previously for Ehrlich ascites cell triglycerides were in good agreement with this hepatoma. Data from these two neoplasms suggest that the metabolic system that regulates or controls the fatty acid composition at the 1 and 3 positions of normal tissue triglycerides does not function normally in neoplasms.     

Application of thin-layer chromatography to the quantitative estimation of tissue triglycerides II. Influence of methyl parathion on the composition of liver triglycerides in the rat

Methyl parathion fed at 10 ppm in a high protein low fat diet inhibited 46.9% of the total liver carboxylesterase activity. The total fatty acid composition of liver triglycerides was not significantly altered. However, the methyl parathion-fed rats showed a higher percentage of saturated acids in the 2-position of the glyceride molecule. Triglyceride analysis employing the multiple TLC-GLC technique (5) also showed a slightly higher percentage of saturated glycerides and those containing 1 and 2 double bonds than those in the control group. Triglyceride patterns in both groups were in general agreement with those calculated from the fatty acid distribution as suggested by Vander Wal (11). Presented at the AOCS meeting in Houston, Texas, April, 1965.     

The influence of dietary medium chain triglycerides on rat mammary tumor development

The N-nitrosomethylurea rat mammary tumor model was used to compare the tumor-promoting effects of a highfat (HF) diet containing a 3:1 mixture of medium chain triglycerides (MCT) and corn oil with that of a HF and a low-fat (LF) corn oil diet. The serum and tumor lipid content and fatty acid (FA) composition were also determined in the three dietary groups. It was found that the MCT-containing diet failed to promote tumor development compared with the HF corn oil group. Tumor incidence in the HF-MCT group was similar to that of the LF corn oil group (5% fat, w/w), but significantly decreased compared to the HF corn oil group. Total serum cholesterol levels were significantly depressed in the HF corn oil group compared to the HF-MCT and LF corn oil groups. Analysis of serum and tumor FA profiles indicated that the HF corn oil group exhibited approximately twice the amount of linoleic acid (LA) as the other two treatment groups. Differences among the three groups in the major FA metabolite of LA, arachidonic acid, were minimal. These results are consistent with the hypothesis that tumor promotion by dietary fat is more a function of the type than the amount of fat ingested. In addition, they indicate that MCT, due at least in part to their unique structural and physiological properties, exert markedly different effects on mammary tumor development than conventional long chain unsaturated fatty acids. Presented at the symposium on “Specialty Lipids and Their Biofunctionality” at the annual meeting of the American Oil Chemists' Society, Philadelphia, May 1985.     

Nutritional evaluation of medium-chain triglycerides in the rat

Nutritional evaluation of a medium-chain triglyceride (MCT) preparation, containing about 75% octanoic acid and 25% decanoic acid, was carried out in short- and long-term experiments in rats. A casein diet containing 19.6% MCT and 2.5% safflower oil, the latter to supply essential fatty acids, was compared with similar diets containing conventional dietary fats. Data obtained in a 47-week study showed that the MCT diet supported normal growth and development. At autopsy, carcass protein and ash levels, vital organ weights and composition were similar to those in rats fed conventional fats. Histological study showed that intestinal and liver sections were normal after 47 weeks on the MCT-containing diet. In general, rats fed MCT had slightly lower growth rates and caloric efficiency values, less carcass fat and smaller epididymal fat pads than animals fed conventional dietary fats. Little C₈ and C₁₀ were found in depot fat. The MCT diet also supported normal reproducton, as indicated by litter size and number. During lactation the volume of milk secreted by the rats receiving the MCT diet was smaller and contained a lower level of fat than that secreted by the rats receiving an oleo oil diet, resulting in slower gains in weight in the MCT group. After weaning, growth of the rats fed MCT compared favorably with that attained by the animals on the diet containing oleo oil.     

Animal endogenous triglycerides: III. Swine,rat and chicken liver: Comparison with adipose tissue

The endogenous triglycerides of swine, rat and chicken livers were fractionated by silver ion thin layer chromatography and the resulting fractions were analyzed for their fatty acid composition and distribution. Whereas the endogenous triglycerides of swine adipose tissue differ markedly from those of rat and chicken adipose tissue in the location of the major fatty acids, the liver triglycerides of the three species are quite similar. They also resemble rat and chicken adipose triglycerides.     

On the structure of the liquid state of triglycerides

Neutron diffraction data on trilaurin were recently presented by Cebulaet al. [Cebula, D.J., D.J. McClements, M.J.W. Povey and P.R. Smith,J. Am. Oil Chem. Soc. 69:130 (1992)] with an interpretation of a liquid structure related to the nematic state of liquid crystals. Arguments for an alternative interpretation, consistent with curved stacks of bilayer units proposed earlier, are presented in this paper, based mainly on the analogy in diffraction behavior with polar lipid liquids/L2-phases.     

Hydrolysis of triglycerides in the isolated perfused rat lung

The purpose of this study was to investigate the hydrolysis of saturated and unsaturated triglycerides by lung lipoprotein lipase and to measure the incorporation of triglyceride fatty acids into lung tissue lipids. Lipolytic activity was studied in the isolated ventilated rat lung, perfused for 100 min in a recycling system with Krebs Ringer bicarbonate containing bovine serum albumin, 5.6 mM glucose, and 1.5 or 10 mM triglyceride. Saturated triglycerides were hydrolyzed at significantly (p<0.05) lower rates than unsaturated triglycerides; tricaprylin, trimyristin and tripalmitin were hydrolyzed at 8.1+1.8, 5.4+1.5 and 9.5+1.8 μmol free fatty acids/g dry wt/100 min, respectively, whereas triolein and trilinolein were hydrolyzed at 20.2+1.8 and 20.6+0.3 μmol free fatty acids/g dry wt/100 min, respectively. The polyunsaturated triglycerides, trilinolein and triarachidonin were hydrolyzed at even higher rates (44.3+3.0 and 50.9+5.4 μmol free fatty acids/g dry wt/100 min, respectively). Intralipid infused at a concentration of 10 mM triglyceride was hydrolyzed at a significantly higher rate than at 1.5 mM triglyceride (58+6.3 μmol free fatty acids/g dry wt/100 min vs 16.6+1.7 μmol free fatty acids/g dry wt/100 min, respectively). Labeled unsaturated triglycerides were broken down at significantly higher rates than labeled saturated triglycerides. Incorporation of triglyceride-fatty acid into lung lipid was greater into neutral lipids than into phospholipids. The data suggest that (a) the factors that appear to affect lung lipoprotein lipase activity are composition and concentration of circulating triglyceride, (b) uptake of fatty acids into the tissue was proportional to the rate of hydrolysis of the emulsion, and (c) triglyceride-fatty acids could therefore be used by the lung for metabolic needs. The data presented in part at the Annual Meetings of the American Physiological Society, Atlanta, GA, April 1981, and the American Thoracic Society, Detroit, MI, May 1981, and published in abstract form-Fed. Proc. 40, 621 (1981), andAm. Rev. Respir. Dis. 123, 219 (1981).     

Changes in the structure of soybean triglycerides during maturation

Soybeans of the Hawkeye variety were picked at eleven periods from 30 to 111 days after flowering and extracted with chloroform-methanol. The triglyceride fraction of five pickings, selected 35 to 91 days after flowering (when synthesis of lipid was most active), were isolated by silicic acid thin layer chromatography (TLC) and species composition determined using argentation TLC and lipase hydrolysis. The triglyceride content of the total lipid increased from 6.5% at 30 days after flowering to 85% in the mature bean (111 days). The major changes in fatty acid composition of the triglycerides occurred during the first 52 days after flowering. During this period linolenic acid decreased from 34.2% to 11.7%, the percentages of linoleic and oleic acids increased, stearic remained fairly constant and palmitic decreased slightly. Large quantitative changes occurred in the molecular species of the triglycerides of the bean during maturation; some triglycerides containing linolenic acid could not be detected approximately 66 days after flowering. Although changes occurred in the percentage and amount of each triglyceride species, the positional distribution of fatty acids remained virtually unchanged throughout maturation. Linolenic acid was distributed fairly uniformly between the β-position and the α-positions, linoleate favored esterification in the β-position, and oleate the α-positions. Most of the stearic and palmitic acids were esterified in the α-positions. The consistency of the positional arrangement of the fatty acids indicated that the mode of glyceride synthesis was established very early during maturation and molecular species composition was controlled by the fatty acids available for synthesis.     

Changes in structure of triglycerides from maturing kernels of corn

Kernels of corn inbred H51 were collected at five intervals after hand pollination. The triglyceride content of the total lipids increased from 8.6% at 10 days after pollination to 78.3% at 60 days. The most active period of triglyceride synthesis occurred from 20 to 45 days after pollination, when the weight of triglycerides per kernel increased from 1.1 to 7.5 mg. Over all the collection periods the percentages of palmitic, linoleic and linolenic acids decreased while oleic acid increased, but from 30 to 60 days after pollination the fatty acid composition of the triglycerides was nearly constant. Stereospecific analysis revealed a general fatty acid pattern for the triglycerides, in which the concentration of the saturated acids was highest in position 1, linoleic acid in 2 and oleic acid in 3. From 20 to 60 days after pollination there was little change in the fatty acid composition at the 1 position, but the largest changes occurred at the 3 position where palmitic and oleic acids decreased 5.1% and 7.3%, respectively, and linoleic acid increased 13.4%. The variations in the molecular species of the triglycerides were determined by silver nitrate thin layer chromatography and were found to be small from 20 to 60 days after pollination, except for an increase in trilinolein from 5.2 to 11.9%. Stereospecific analyses of four major triglycerides species, SMD, M₂D, SD₂, and MD₂, revealed larger changes in fatty acid distribution at individual positions during maturation than were apparent from analyses of the total triglycerides. Presented in part at the AOCS Meeting, Ottawa, September 1972.     

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.     

The distribution of labeled palmitic acid into the diglycerides and triglycerides of rat adipose tissue

After in vitro incubation of rat epididymal fat pads with radioactive palmitic acid, the distribution of the label in the different lipid classes and in different triglycerides was determined by silica gel and silver nitrate-silica gel thin-layer chromatography (TLC). The radioactivity of the diglycerides was approximately half of the triglycerides. This ratio did not change with alteration in the time of incubation. It remained unaltered even after a subsequent 10-min incubation in a nonradioactive medium. When the fat pads were incubated, first with¹⁴C-, then with³H-labeled palmitic acid, the³H/¹⁴C ratio was slightly lower in diglycerides than in triglycerides. The fully saturated molecules contained 38% of the radioactivity of triglycerides. Addition of oleic acid or norepinephrine to the labeled palmitic acid-containing medium decreased this value. Subsequent incubation with these compounds did not alter the distribution of radioactivity.     

A study of the composition of fish liver and body oil triglycerides

Silver-ion high-performance liquid chromatography (Ag⁺-HPLC) was used to study the range and variations in molecular species of triglycerides from industrial, retail and laboratory extracted fish oils. These were contrasted with a typical plant oil. Selected fish oils were fractionated and the fatty acid distribution of the fractions determined by gas-liquid chromatography. Fish oils gave a characteristic Ag⁺-HPLC profile, typified by sharp, intense peaks at the start of the chromatogram and broad, multiple nongaussian peaks for the late eluting components. Triglycerides ranging from those that were wholly saturated to those containing 16 double bonds were isolated. Cod (Gadus spp.), saithe (Pollachius virens) and monkfish (Squatina squatina) liver oils gave similar triglyceride profiles. Mackerel (Scomber scombrus), capelin (Mallotus villosus) and herring (Clupea harengus) body oils gave characteristic triglyceride profiles which were associated with high concentrations of 20∶1 and 22∶1 fatty acids. Only small amounts of these particular triglycerides were observed for menhaden (Brevoortia spp.), South African anchovy (Engraulis capensis) and Indian sardine (Sardinella longiceps) oils, all of which contained minor amounts of these acids. The latter oils contained highly unsaturated triglycerides, whereas only traces of these were noted for the former. Chromatography with Ag⁺-HPLC can be used for the rapid screening of fish oils and for selecting those oils rich in polyunsaturated acids that may be suitable for enrichment. Cottonseed oil gave well-defined and discrete peaks. Similar peaks were observed in the chromatogram of Omega-combination, a mixture of primrose and fish oils. Thus, fish, plant and a mixture of these oils can be readily distinguished.     

The rhodium-catalyzed deuteration of unsaturated triglycerides

Tripalmitolein, triolein, trilinolein and trilinolenin were deuterated with deuterium gas and Wilkinson’s catalyst [(Ph₃P)₃RhCl(I)]. Recrystallization of the products from acetone yielded highly pure deuterium-labelled triglycerides (TG). The deuterated TG were converted to methyl esters and analyzed by gas chromatography/mass spectroscopy to determine the deuterium distribution. Methyl palmitate-9,10-d₂ (from tripalmitolein) and methyl stearate-9,10-d₂ (from triolein) yielded isotopic distributions of 93–97% d₂, methyl stearate-9,10,12,13-d₄ (from trilinolein) of 74% d₄ and methyl stearate-9,10,12,13,15,16-d₆ (from trilinolenin) of only 58% d₆. Because the deuterium-labelled TG were to be used in human metabolism studies, atomic absorption spectroscopy was used to determine if any residual rhodium was present. No rhodium was detected at 70 ppb (the minimum detection limit).     

The component triglycerides of palm-kernel oil

Triglycerides of palm-kernel oil were fractionated by gas liquid chromatography into 13 groups based on their carbon number of 30 to 54. These groups represent 99.9% of the total glyceride content. The proportion of triglyceride types in each group was calculated from the component fatty acids. These groups are defined by the nature of their constituent fatty acids but the position of the acids on glycerol is unknown. These 87 types, 24 of which are given in detail, were found. The two major components are trilaurin (19.8%) and dilauromyristin (14.1%). Only 18 types, occurring in an amount greater than 1%, together represent 80% of the total glycerides. Comparison of the glyceride content with that of coconut oil revealed many similarities between the two oils.     

The structural components of milk triglycerides

Pancreatic lipase hydrolysis and gas chromatographic analysis of two samples of butter fat show that the individual acyl groups are not dispersed at random among all the glyceryl carbons. When considered only as saturated or unsaturated, and not as individuals, they appear to be distributed intermolecularly at random, or nearly so, but tend to assume specific positions intramolecularly. Presented at the 51st annual meeting, American Oil Chemists’ Society, Dallas, Tex., April 4–6, 1960.     

The effect of dietary copper on the structure and physical properties of adipose tissue triglycerides in pigs

The inner back fat of control pigs had a higher melting point and stearic acid-oleic acid ratio than did the outer back fat of the control animals or the inner and outer back fats of pigs given the control diet supplemented with 250 ppm copper. By a combination of argentation thin layer chromatography and pancreatic lipase hydrolysis, it was shown that in the inner back fat of the control animals the proportions of two of the more saturated glyceride species were significantly greater and the proportions of two of the more unsaturated species were less than in the outer back fat of the control animals and in the inner and outer back fats of the copper-fed animals. These findings probably account for the observed differences in melting point. Stereospecific analyses of the glycerides demonstrated that the increased content of stearic acid in the inner back fat of the control pigs was distributed between the 1 and 3 positions.