Lipid composition of prepartum human mammary secretion and postpartum milk.

Changes in lipid composition of mammary secretions of five women were studied at two prepartum periods and compared with composition of colostrum, transitional, and mature human milk. Fat content was approximately 1 g/dl during early (-42.0 days before parturition) and late (-9.5 days) prepartum periods and increased to 3-4 g/dl in colostrum (3.0 days post partum), transitional (7.2 days), and mature milk (56.2 days). Most of the lipid present was triglyceride either pre- (93%) or post- (97%) partum. All fat globule core lipids, with the exception of 1,3-diglycerides, increased from prepartum concentrations to levels usually found in milk. Prepartum secretions contained higher amounts of the membrane components, phospholipid (3.2 g/dl), cholesterol (2.3 g/dl), and cholesteryl ester (1.1 g/dl), which declined postpartum to 0.65, 0.37, and 0.09 g/dl, respectively. Thus, the content of core lipids exhibited an opposite pattern to the content of membrane lipids pre- and postpartum. With regard to synthesis of fatty acids, prepartum secretory mechanisms appeared to be very similar to those occurring postpartum since fatty acid composition of prepartum secretions closely resembled that of postpartum milk.