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Stearic Acid Metabolism by Mammary Cells

Department of Food Science, Cornell University, Ithaca, New York 14850

ABSTRACT

Dispersed cells, from lactating bovine and rat mammary glands, and bovine mammary tissue slices avidly absorbed and metabolized substrate 1-¹⁴C-stearic acid. Absorbed stearic acid was extensively desaturated to oleic acid by ruminant cells. Freshly dispersed cells from the cow surpassed all other preparations in absorption and desaturation of stearic acid.

The preponderance of radioactive substrate was esterifled into glycerides, mainly triglycerides (>70%); the remainder (15 to 20%) was incorporated into phospholipids and 1 to 2% into cholesterol esters. Measurable labeled triglycerides were secreted into the culture media from functional bovine and rat cells. In bovine and rat mammary cells, radioactive stearic and oleic acids were esterifled mostly into triglyceride molecules with C40 to C52 aggregate acyl carbons, i.e. high molecular weight triglycerides, resolved by gas chromatography.

The preponderance of the radioactivity in the phospholipids was associated with phosphatidylcholine, though all classes including phosphatidic acid contained measurable radioactivity.

Distribution of radioactivity between stearic and endogenous oleic acid in various lipid classes and on specific positions of glycerolipids was also examined. Relative concentration of oleic acid was greatest in phospholipids where it was on positions sn1 and sn2 of the glycerol moiety. In triglycerides labeled oleic acid was mostly on the primary positions of the glycerol moiety.

These observations are discussed with respect to corresponding data from in vivo studies of milk lipid biosynthesis.