Composition of molecular species of triacylglycerols in bovine milk fat.

Triacylglycerols from bovine milk fat were fractionated by reversed-phase liquid chromatography. The fatty acid and triacylglycerol compositions of each fraction were determined by capillary gas chromatography. These data were used to determine the accurate proportions of 223 individual molecular species of even-numbered triacylglycerols, accounting for 80% of total triacylglycerols (all percentages are expressed as moles per 100 mol). The three major triacylglycerols were butyroylpalmitoylacylglycerols, namely butyroylpalmitoyloleoylglycerol (4.2%), butyroyldipalmitoylglycerol (3.2%), and butyroylmyristoylpalmitoylglycerol (3.1%). Twenty-two triacylglycerols (> 1%) contained at least two of the four major long-chain fatty acids (C14:0, C16:0, C18:0, and C18:1). Among them were eight butyroyldiacylglycerols, the proportions of which reached 19% in total but only 12% when calculated on the basis of a random distribution of the fatty acids in the triacylglycerol molecules. More generally, most of the triacylglycerols that are composed of a short-chain fatty acid (C4:0 or C6:0) and two fatty acids in the range of C12 to C18 are preferentially synthesized by the mammary gland; their proportions (36% in total) were higher than the corresponding random values (24% in total). Conversely, the total amounts of simple (.4%) and mixed (2.9%) saturated long-chain (C14:0 to C18:0) triacylglycerols were much lower than those expected from random calculation (1.9 and 6.1%, respectively).

Age-related changes in delta 6 and delta 5 desaturase activities in rat liver microsomes.

Age-related changes in delta 6 desaturation of [1-14C]alpha-linolenic acid and [1-14C]linoleic acid and in delta 5 desaturation of [2-14C]dihomo-gamma-linolenic acid were studied in liver microsomes from Wistar male rats at various ages ranging from 1.5 to 24 mon. Desaturase activities were expressed both as specific activity of liver microsomes and as the capacity of whole liver to desaturate by taking into account the total amount of liver microsomal protein. delta 6 Desaturation of alpha-linolenic acid increased from 1.5 to 3 mon and then decreased linearly up to 24 mon to reach the same desaturation capacity of liver measured at 1.5 mon. The capacity of liver to desaturate linoleic acid increased up to 6 mon and then remained constant, whereas microsomal specific activity was equal at 1.5 and 24 mon of age. The capacity of liver to convert dihomo-gamma-linolenic acid to arachidonic acid by delta 5 desaturation decreased markedly from 1.5 to 3 mon. It then increased to reach, at 24 mon, the same level as that observed at 1.5 mon. Age-related changes in the fatty acid composition of liver microsomal phospholipids at the seven time points studied and of erythrocyte lipids at 1.5 and 24 mon were consistent with the variations in desaturation capacity of liver. In particular, arachidonic acid content in old rats was slightly higher than in young rats whereas contents in linoleic and docosahexaenoic acids varied little throughout the life span.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of simvastatin on desaturase activities in liver from lean and obese Zucker rats.

The effect of simvastatin, a hypocholesterolemic drug, on the biosynthesis of arachidonic acid was studied in obese and lean Zucker rats. After administration of 2 mg/kg body weight/d for 13 d, delta 6 and delta 5 desaturase activities were measured in liver microsomes at two substrate concentrations. In untreated rats, the delta 6 desaturation rate was similar in the obese and lean rats when measured at saturating substrate levels, whereas delta 5 desaturation was lower in the obese animals. Treatment with simvastatin did not change delta 6 desaturation in either phenotype but increased delta 5 desaturation in obese rats to reach the unchanged rate observed in lean animals. The changes were not reflected in the fatty acid composition of liver microsomal phospholipids when expressed as micrograms fatty acid/g of liver.

Determination of bovine butterfat triacylglycerols by reversed-phase liquid chromatography and gas chromatography.

Triacylglycerols (TGs) from a sample of summer butterfat (bovine milk) were analysed and fractionated by reversed-phase liquid chromatography (RPLC). Fatty acid and TG composition of eac of the 47 RPLC fractions ranging from 0.1 to 6.9% were determined by capillary gas chromatography. The data were used together to determine the quantitative composition of the molecular species of TGs. A large number of TG species, accounting for 80% of the total, could be unequivocally identified and individually determined. The combination of the chromatographic methods used proved to be a powerful and accurate approach for the determination of molecular species of TGs in a complex fat, but also a difficult and time-consuming task.

Effects of age and dietary essential fatty acids on desaturase activities and on fatty acid composition of liver microsomal phospholipids of adult rats.

The combined effects of age and dietary n-6 and n-3 fatty acids were studied in 3-, 6- and 9-month-old rats. At each age, two groups were fed diets containing 5% (w/w) of vegetable oils rich in either 18:3n-6 (borage group) or 18:3n-6 plus 18:4n-3 (black currant group), for a period increasing with age. A control group was fed the essential fatty acids 18:2n-6 and 18:3n-3 only. For each group, delta 6, delta 5 and delta 9 desaturase activities were measured in liver microsomes, and fatty acid composition was determined in microsomal phospholipids. Desaturase activity varied as a function of age and dietary lipids. delta 6 Desaturation of 18:3n-3 was more sensitive to these factors while delta 6 desaturation of 18:2n-6 and delta 9 desaturation were more dependent on season than the other two. Desaturase activity was influenced more by the black currant than by the borage diet, especially at 6 and 9 months of age. A large proportion of arachidonic acid was maintained in the microsomes independent of the diet. Changes in the fatty acid composition did not strictly reflect the differences in desaturase activities. The effects of the two factors (age and diet) on the activities of the desaturases are complex, suggesting that the enzymes are susceptible to other factors as well.