J. Tinoco

Linolenic acid deficiency.

Linolenic acid deficiency has not been demonstrated clearly in warm blooded animals, yet circumstantial evidence suggests that n−3 fatty acids may have functions in these animals. The fact that several species of fish definitely require dietary n−3 fatty acids indicates that n−3 fatty acids have important and specific functions in these animals and suggests that such functions may also be present in warm blooded animals. It is also true that n−3 fatty acid distribution in tissues of birds and mammals appears to be under strict metabolic control, and that this complex metabolic control mechanism apparently has survived evolutionary pressure for a very long time. So far, attempts to produce linolenic acid deficiency in mammals have not revealed an absolute requirement for n−3 fatty acids. If functions for n−3 fatty acids do exist in warm blooded animals, it seems probable that they may be located in the cerebral cortex or in the retina, because these tissues normally contain high concentrations of n−3 fatty acids.

Linolenic acid deficiency: Changes in fatty acid patterns in female and male rats raised on a linolenic acid-deficient diet for two generations

Rats were fed for two generations a purified, linolenic acid-deficient diet in which the only source of lipid was purified methyl linoleate. This diet contained about 38 mg linolenic acid/kg diet. Control rats were given the same diet supplemented with methyl linolenate (2,500 mg/kg diet). Male and female rats ranged in age from weanling pups to adults. Lipids were extracted from liver, brain, kidney, spleen, heart, muscle, gastrointestinal tract, lung, ovary, testis, adrenal, plasma, erythrocytes, retina, and adipose tissue. Fatty acids of major phospholipid classes (choline phosphoglycerides, ethanolamine phosphoglycerides, and mixed serine phosphoglycerides plus inositol phosphoglycerides) or of total lipid extracts were measured by gas liquid chromatography. Growth rates and organ weights were similar in control and linolenic acid-deficient rats. The major effect of the deficiency was to lower the proportions of n−3 fatty acids, especially 22∶6 n−3, in all the organs analyzed. Docosahexaenoic acid (22∶6 n−3) was mainly replaced by 22∶5 n−6 in deficient rats. The greatest changes in composition were found in brain, heart, muscle, retina, and liver.

Monolayer interactions of individual lecithins with natural sterols

Abstract In order to find the features of molecular structure responsible for interactions between sterols and lecithins in monolayers at the air-water interface, we have measured mixed monolayers containing one pure sterol and one molecular species of lecithin in different mole ratios. Four naturally-occurring sterols and nine synthetic lecithins were used. Cholesterol, β-sitosterol, dihydrocholesterol, and ergosterol were examined in mixtures with 1,2-dipalmitoyl-, 1-palmitoyl-2-oleoyl-, 1-palmitoyl-2-linoleoyl-, 1-palmitoyl-2-linolenoyl-, 1-palmitoyl-2-arachidonoyl-, 1,2-distearoyl-, 1-stearoyl-2-linoleoyl-, 1-stearoyl-2-linolenoyl- and 1-stearoyl-2-arachidonoyllecithins. In addition, the interactions of 5-α-androstane-3-β-ol with the first three palmitoyl-lecithins were investigated. All sterols condensed strongly with 1,2-dipalmitoyllecithin at low pressures (5 dynes/cm) and this condensation was much less at 40 dynes/cm. Cholesterol and β-sitosterol produced the greatest condensations in all lecithin films, and these condensations were greater at low pressures. These results suggest that differences in the aliphatic side chain have little influence on the behavior of these sterols in mixed monolayers with lecithins. Dihydrocholesterol (cholestanol), ergosterol and 5-α-androstane-3-β-ol produced much smaller condensations in lecithin monolayers, and in these cases also, condensations were usually less at 40 than at 5 dynes/cm. The difference between these sterols and the other sterols is mainly in the B-ring, which suggests that a B-ring with a double bond at C 5 favors condensation much more than either a saturated B-ring (dihydrocholesterol and androstanol) or one with double bonds at C 5 and C 7 (ergosterol).

Depletion of docosahexaenoic acid in retinal lipids of rats fed a linolenic acid-deficient, linoleic acid-containing diet

Rats were raised for 2 generations on a diet in which 1.25% methyl linoleate was the only source of fat. Control rats were given 1.0% methyl linoleate plus 0.25% methyl linolenate. Lipids were extracted from retinas and their fatty acids were analyzed by gas-liquid chromatography. Docosahexaenoic acid accounted for 33.8% of total fatty acids in control retinas, for 13% of fatty acids in first-generation deficient retinas, and for 2.7% of fatty acids in second-generation deficient retinas.

Effects of estradiol and testosterone on the incorporation and distribution of [Me-14C]methionine methyl in rat liver lecithins

Abstract 1. 1. Castrated male rats were injected for 3 weeks with testosterone propionate (2 mg/week), estradiol benzoate (100 μg/week) or sesame oil alone (0.3 ml/week). They were injected intraperitoneally with 3.3 μC of [Me-14C]methionine per 100 g body weight 1 h before they were killed. 2. 2. Liver phosphatidylethanolamines and lecithins were separated by thin-layer chromatography, and radioactivity and fatty acids were determined. In addition, lecithins were separated, according to unsaturation, into tetraenes (mainly 20:4, but contained 22:5 and 22:6 fatty acids also), triene, diene, and monoene subfractions by AgNO3-silicic acid thin-layer chromatography, and counted. 3. 3. Estradiol increased the incorporation of the methyl label into the lecithins, whereas testosterone had neither a stimulatory nor inhibitory effect. 4. 4. Estradiol increased proportions of stearic acid and polyenoic acids (> 20:4) and decreased linoleic acid in liver lecithins as compared with the other groups. 5. 5. The largest part of the methyl label in the lecithins of all groups was in the tetraene subfraction (> 65%) which also had the highest specific activity. The next largest portion was in the diene subfraction. The methyl label incorporation into the lecithin subfractions was closely associated with the amount of a given fraction in the total lecithins. 6. 6. Estradiol increased the stearic acid content and the proportion of the tetraene subfraction while decreasing the relative proportion of the diene subfraction. 7. 7. A close relation between the labeled choline of the lecithins and the content of stearic acid in a given fraction was observed for all groups—a relationship not shown by palmitic, oleic or linoleic acids. 8. 8. The results indicated that estradiol enhanced the methylation of phosphatidylethanolamine and increased the formation of lecithins containing stearic and long-chain polyene fatty acids (20:4 and higher). The relationship of the labeled choline to stearic acid and the highly unsaturated fatty acids suggested that fatty acid composition influenced the methylation of phosphatidylethanolamines.

Sex differences in the metabolism of phosphatidyl cholines in rat liver

Abstract 1. 1. Mature male and female rats were injected intraperitoneally with tracer doses of [ Me - 14 C]methionine, then were killed 20, 40, 60, and 120 min afterwards. 2. 2. Liver phosphatides from both sexes were separated by thin-layer chromatography and the phosphatidylcholine (PC) divided into 3 subfractions. Determinations of fatty acid composition and measurements of radioactivity of the phosphatide fractions were made. 3. 3. The fatty acid composition of the fastest-moving PC subfraction resembled that of the phosphatidylethanolamine fraction and had a higher proportion of stearic and arachidonic acids than did the other slower-moving fractions. 4. 4. Female rats had a higher proportion of stearic and arachidonic acids in their fast moving PC than did males and the specific activity of this fraction was also higher in females. 5. 5. The results indicated that methylation of phosphatidylethanolamine produced PC having a high proportion of stearic and arachidonic acids. The sex difference in these fatty acids in the liver PC appeared to have resulted from the higher rate of PC synthesis via methylation in female rats than in males.

Behavior of specific natural lecithins and cholesterol at the air water-interface

Abstract Individual molecular species of lecithins were mixed with cholesterol and their pressure-area curves were measured at the air-water interface at 22±1°. The lecithins investigated were: L-16:0-16:0-, D-16:0-16:0-, L-16:0-18:3-, L-18:0-18:3-, L-16:0-20:4-, L-18:0-20:4- and L-18:0-18:0-lecithins. All of these except the D-16:0-16:0- and L-18:0-18:0-lecithins have been found in nature. Considerable condensation of monolayers with cholesterol was observed in all cases except that of 18:0-18:0-lecithin, in which there was little condensation. The naturally-occurring structure of lecithins, that is, 1-saturated-2-unsaturated, leads to large condensations in mixed monolayers. This geometrical fit between cholesterol and lecithins may be of importance in enzyme reactions involving cholesterol or lecithins.

A micromethod for fractionation of lipids by silicic acid chromatography

Abstract A micromethod has been presented for separating, by silicic acid chromatography, 1–10 mg of a complex mixture of lipid of biological origin into four fractions: I, cholesterol ester; II, triglycerides; III, free cholesterol, free fatty acids, and mono- and diglycerides; and IV, phospholipids. The method was found to be rapid, convenient in handling, quantitative, and eminently suitable for further analysis of the fractions by gasliquid chromatography.

Monolayers of sterols and phosphatidylcholines containing a 20-carbon chain

Pressure-area curves of monolayer films were measured for phosphatidylcholines (PC) in which the 1-position was occupied by palmitic acid and the 2-positions were occupied respectively by: 20 : 0,20 : 1n9, 20 : 2n6, 20 : 3n3, 20 :3n6, 20 :3n9, 20 :4n6 or 20 : 5n3 fatty acids. The interactions of these PC with cholesterol or desmosterol were studied. Fully saturated PC (16 : 0--20 : 0) displayed a relatively small molecular area. The presence of one double bond greatly increased the molecular area, but a second double bond resulted in only a small additional increase in area. A third double bond caused a further large expansion in area, but the presence of a fourth or fifth double bond had little additional effect. Condensation of molecular area was observed with all sterol/PC mixed films. Approximately equimolar mixtures of sterols and unsaturated PC condensed maximally, but 16 : 0--20 : 0 PC condensed most in mixtures containing 20--30 mol% of either sterol. The extent of condensation varied with surface pressure. The pressure at which maximum condensation occurred depended upon the structure of the PC and was always 20 dyn/cm or lower. The pressure at which maximum condensation with cholesterol occurred increased with increasing unsaturation of the PC.

Feeding pure docosahexaenoate or arachidonate decreases plasma triacylglycerol secretion in rats

Essential fatty acid (EFA)-deficient rats were fed highly purified methyl esters of docosahexaenoate (22∶6n−3), arachidonate (20∶4n−6), alpha-linolenate (18∶3n−3) or oleate (18∶1n−9) (100 mg/day, tube fed for 3–10 days), and their plasma triacylglycerol (TG) secretion rates were measured. Secretion rates of TG into plasma were reduced by tube-feeding 22∶6n−3, 20∶4n−6, 18∶3n−3, but not 18∶1n−9, to EFA-deficient rats. A significant reduction occurred after feeding 22∶6n−3 for only three days. Feeding 22∶6n−3 or 18∶3n−3 to EFA-deficient rats for three days also reduced the activities of liver lipogenic enzymes and sharply increased the proportions of 22∶6n−3 and 20∶5n−3 in liver phospholipid fractions. Mechanisms by which these EFA may reduce lipogenesis are discussed.