Interrelationships between the major fatty acids present in the lecithin isolated from the plasma of experimental rabbits

Dietary fatty acids and the plasma phospholipids of the lactating cow

Cows were given either a low-fat concentrate mixture or a concentrate mixture that contained 5 or 10% ‘stearic acid’ (85% pure) or 10% ‘palmitic acid’ (85% pure). The concentrate mixtures were given with a high roughage diet that supplied 4·4 kg of hay and 2·7 kg of sugar-beet pulp/day. Blood samples were taken from the cows on each dietary treatment and the plasma phospholipids were analysed.

Phosphatidyl choline accounted for 70% of the plasma phospholipids when the cows were given the low-fat diet and about 86% of the plasma phospholipids when the cows were given the diets supplemented with the fatty acids. The inclusion of the fatty acids in the concentrate mixtures decreased the relative proportions of the plasma phosphatidyl ethanolamine, sphingomyelin and lysophosphatidyl choline but the relative proportion of the plasma phosphatidyl serine remained unchanged.

When the diet was supplemented with stearic acid the concentrations of 18:0 and 16:0 in the phosphatidyl choline were unaltered but the concentration of 18:1 was increased and the concentration of 18:2 was decreased. When the diet was supplemented with palmitic acid the concentrations of 16:0 and 18:1 in the phosphatidyl choline were increased and the concentrations of 18:0 and 18:2 were decreased. In contrast, the inclusion of stearic acid in the diet increased the concentration of 18:0 in the phosphatidyl serine and decreased the concentration of 16:0; the concentrations of 18:1 and 18:2 were unchanged. The fatty acid composition of the plasma phosphatidyl ethanolamine was unaffected by dietary treatment. The effects of diet on the fatty acid compositions of the phosphatidyl choline and lysophosphatidyl choline were similar. Supplementation of the diet with stearic acid increased the concentrations of 18:0 and 18:1 in the plasma sphingomyelin and decreased the concentrations of 16:0 and 18:2. The addition of palmitic acid to the diet increased the concentration of 16:0 in the sphingomyelin but it decreased the concentrations of the other constituent fatty acids.

Dietary linoleic acid and the plasma phospholipids of the rabbit

1. Groups of rabbits were given diets containing different proportions of butterfat and maize oil. After the animals had been given the experimental diets for 40 weeks the plasma phospho- lipids were fractionated and the fatty acid composition of each fraction was determined.

2. Phosphatidyl choline and lysophosphatidyl choline accounted for about 75 and 12% respectively of the total plasma phospholipids: phosphatidyl ethanolamine, sphingomyelin and phosphatidyl serine accounted for only about 5.3, 5.0 and 2.6% respectively. Changes in the linoleic acid content of the diet had little effect on the relative proportions of the individual plasma phospholipids, but there was an over-all decrease in the concentration of total phospholipids in the plasma as the linoleic acid content of the diet was increased from 0.25 to 10.6%.

3. When the diet contained 0.25 % linoleic acid, the linoleic acid:oleic acid ratio in the phosphatidyl choline (1.3) was similar to that in the phosphatidyl ethanolamine (1.2), but as the linoleic acid content of the diet was increased to 10.6% the linoleic acid:oleic acid ratio in the phosphatidyl choline increased to 48, whereas that in the phosphatidyl ethanolamine increased only to 2.2. Increases in the linoleic acid content of the diet resulted also in increases in the linoleic acid:oleic acid ratios in the phosphatidyl serine, lysophosphatidyl choline and sp hingomyelin.

4. When the linoleic acid content of the diet was increased, the stearic acid:palmitic acid ratio in the phosphatidyl choline increased, whereas it decreased in the phosphatidyl ethanol- amine and remained relatively unaltered in the phosphatidyl serine. The stearic acid contents of the lysophosphatidyl choline and sphingomyelin were unaltered by dietary treatments, but the palmitic acid content of these two phospholipids decreased as the linoleic acid content of the diet increased.

5. The results are discussed in terms of the metabolic relationships that exist between the various phospholipids.

The effect of diets containing different proportions of butterfat and maize oil on plasma lipids and aortic atherosis in rabbits

1. Seven groups of male rabbits (thirteen to fifteen per group) were givenad lib. a diet consisting of 80 parts of a low-fat basal ration to which were added 20 parts of fat in the form of butterfat, maize oil or various mixtures of the two.

2. After 40 weeks, samples of blood were taken and the animals were killed. The concentrations of total cholesterol and phospholipid in the plasma and the fatty acid compositions of the plasma cholesteryl esters and phospholipids were determined. The degree of atheromatous degeneration was determined in the aortas.

3. Little aortic atherosis was observed in the rabbits given the diets containing 0, 10 and 12% butterfat, but as the butterfat content of the diet was increased above 12%, pronounced increases occurred in the extent of atheromatous degeneration of the aorta. The concentration of cholesterol in the plasma increased progressively as the butterfat content of the diet was increased and the maize oil content was decreased. There was an inverse curvilinear relationship between the degree of aortic atherosis and the phospholipid: cholesterol ratio in the plasma.

4. The concentration of linoleic acid in the plasma cholesteryl esters was inversely related to the concentration of cholesterol in the plasma, and the concentration of linoleic acid in the plasma phospholipids was inversely related to the concentration of phospholipids in the plasma. There was a positive linear relationship between the stearic: palmitic acid ratio and the linoleic: oleic acid ratio in the plasma phospholipids.

The transport of phospholipids from the yolk to the yolk-sac membrane during the development of the chick embryo

A study was made of the concentrations and fatty acid compositions of the various phospholipid fractions in the yolks and yolk-sac membranes at different stages in the development of the chick embryo. Phosphatidyl choline was the major component of both the yolk and membrane phospholipids. The composition of the yolk phospholipids was broadly similar to that of the membrane phospholipids. In both the yolk and membrane phospholipids, the proportions of phosphatidyl choline and phosphatidyl ethanolamine tended to decrease, whereas the proportions of phosphatidyl serine, sphingomyelin, and lysophosphatidyl choline tended to increase as incubation proceeded. The fatty acid composition of the yolk phosphatidyl choline did not change during incubation, but there was a progressive decrease in the palmitic acid: stearic acid ratio in the membrane phosphatidyl choline. The changes in the fatty acid composition of the yolk phosphatidyl ethanolamine indicated that there was a preferential absorption from the yolk of phosphatidyl ethanolamine with stearic acid in the α position and arachidonic or docosahexaenoic acids in the β position. The lysophosphatidyl choline in the yolk and membrane evidently consisted of mixtures of the 1-acyl and 2-acyl isomers. There was no evidence that extensive breakdown and resynthesis of phospholipids occurred during the transport of lipids from the yolk to the yolk-sac membrane.