Composition of adipose tissue triglycerides of neonatal and year‐old lambs

Triglyccrides were isolated from perinephric (internal) and subcutaneous (external) adipose tissue obtained from neonatal lambs and from lambs which had been fed, until they were a year old, on a semi‐synthetic ration or on a diet of grass cubes. the triglycerides went analysed for their fatty acid composition (including trans unsaturated acids) and for the intramolecular distribution of these acids between the primary and secondary alcoholic groups of the glycerol moiety. Whereas in the year‐old lambs (and in adult sheep previously examined), the triglycerides of internal adipose tissue had a higher content of stearic acid and trans unsaturated acid than those of external tissues, the triglycerides from the perinephric and subcutaneous tissues of the neonatal lambs were very similar in fatty acid composition. Palmitic acid and C 18 mono‐unsaturated acid together constituted more than 80% of the total acids. This composition resembles that of the subcutaneous triglycerides of the grown animal and suggests that, at all stages of growth, the triglycerides of external tissues are largely the result of endogenous synthesis. The fatty acids of the adipose tissues of the neonatal animals did not contain any of the acids of exogenous origin, such as those with trans double bonds, which characterise the triglycerides of the growing and mature animals, particularly those of the internal depots. Nevertheless, the intramolecular disposition of the fatty acids in the triglycerides formed in utero was similar to that previously observed in triglycerides from both the internal and external depots of the adult sheep. Saturated acids (palmitic and stearic acids) predominated amongst those esterified in the 1‐and 3‐positions of the glycerol moiety and unsaturated acids (almost entirely oleic acid) were the major components esterified in the 2‐position. While the triglycerides from corresponding body sites in the two groups of year‐old lambs were generally quite similar with respect to their content of palmitic acid, stearic acid and C 18 mono‐unsaturated acid, the contribution of trans isomer to the total C 18 mono‐unsaturated acid was considerably greater in the tissues (particularly perinephric tissue) of the animals fed on grass cube than in the tissues of those given the semi‐synthetic ration. This difference between the two groups of lambs was associated with a corresponding difference in the proportions of C 18 trans unsaturated acid in the lipids of the rumen contents of the animals.