Structure and Synthesis of Milk Fat. IV. Role of the Mammary Gland with Special Reference to the Cholesterol Esters

Abstract

Using intramammary infusion of both labeled and unlabeled fatty acids, it was demonstrated that cholesterol esters, glycerides, and phospholipids of milk are all made from fatty acids within the mammary gland. Diverse evidence from this and other studies suggests that most, if not all, of the ester lipids of milk are synthesized from a common pool of fatty acids within the mammary gland. A remarkably active metabolic role is indicated for the cholesterol esters of milk. In the case of both labeled (palmitate-l-Cl4) and unlabeled (linoleate) infusates, uptake by the cholesterol ester fraction was more intense and, by tracer, more rapid than for the glycerides or phospholipids. Some compositional data on cholesterol esters of milk are also presented.