The lipid composition of normal rat thymus

Abstract

Thymic lipids (representing 2.6% of tissue wet weight) from two strains of normal, adult, white rats have been subjected to a variety of chromatographic techniques and chemical analyses leading to the complete separation and quantification of lipid components. Neutral lipids and phospholipids were separated on silicic acid by a batch procedure; neutral lipids represented from 66 to 80% of total lipids. Individual neutral lipids were separated isolated using column chromatography on Florisil; neutral lipids were mainly triglycerides (82–85%), with cholesterol (6–10%) and cholesterol esters (3–4%) representing significant contributions to the total; smaller amounts of lower glycerides and free fatty acids were also present. Individual phospholipids were separated isolated by two-dimensional thin-layer chromatography on Silica Gel G; 8 phospholipids were identified with phosphatidyl choline (49–50% of total), phosphatidyl ethanolamine (19%), phosphatidyl inositol (12%), sphingomyelin (10–11%), phosphatidyl serine (5–7%) representing the main components; small amounts of lysolecithin, phosphatidic acid and cardiolipin were also present. The fatty acid composition of the isolated lipid fractions was determined by quantitative gas-liquid chromatography. Among the neutral lipids, unsaturated fatty acids predominated (48–80% of total acids); among unsaturated fatty acids, oleic linoleic represented the largest proportion, although in certain of the lower glycerides hexadecatrienoic acid represented 35 to 52% of total fatty acids; of the saturated acids, palmitic, stearic and arachidic acids constituted the majority. Unsaturated fatty acids predominated in most, but not all, of the phospholipids; this relationship depended on the strain of rat. Although oleic, linoleic and linolenic acids comprised a large portion of the unsaturated acids, large amounts of C 20 to C 24 polyunsaturated acids were also found in all phospholipids. Palmitic, stearic, arachidic and behenic acids represented the bulk of the saturated acids in phospholipids; however, large amounts of 26: o were also found in a number of phospholipids.