Development of the capacity of mouse mammary glands for medium chain fatty acid synthesis during pregnancy and lactation.

The time-course for appearance of fatty acid synthetase and thioesterase II, enzymes required for the synthesis of medium chain (C8--C12) fatty acids by the mammary gland, has been studied in the mouse and compared with that in the rat. The development of high levels of fatty acid synthetase in the mouse mammary gland during the early days of lactation coincided with an observed increase in the overall lipogenic capacity of the gland, assessed by measuring the incorporation of radioactive acetate into fat in tissue slices. Both the level of thioesterase II in the gland and the proportion of medium chain fatty acids synthesized from acetate by tissue slices began to increase in late gestation but did not reach a maximum until lactation was well established. In this regard the mouse is distinctly different from the rat, which establishes maximum levels of thioesterase II in the mammary gland prior to parturition. The significance of this difference as it relates to mammary gland development is discussed.