This proposal was prepared in response to the announcement of a Research Program on Breastfeeding and Human Milk. We are specifically addressing th section of the program announcement headed Processes Involved in Milk Formation and Secretion, proposing studies which will determine how choline influences milk formation and secretion. Choline is necessary for normal growth and development. It is a precursor for the biosynthesis of phospholipids - essential components of all membranes, it is an important methyl donor, and it is needed to make acetylcholine. Most mammals derive much of their daily choline requirements from their diets, and milk is an important dietary source of choline. Choline moiety is needed to make the phosphatidylcholine which coats the secretory vesicles and milk fat globule made within the mammary epithelial cell. In hepatocytes, choline is absolutely required for the export of a fat globule (VLDL). It is possible that varying the availability of choline might alter the excretion of casei and lipid by the mammary epithelial cell. Our laboratory has made the following observations: 1) Neonatal rats, ferrets and humans have extremely high blood choline concentrations - making more choline available to tissues; 2) The above is, in part, due to ingestion of milk which is high in choline content; 3) There is a large increase (6-fold) in the choline concentration of human milk just after the start of lactation, followed by an equally large decrease in choline content 4-5 days later; 4) Mammary epithelial cells are capable of accumulating choline via mediated transport so that milk choline concentration can be 70-fold higher than is maternal blood choline concentration; 5) Mammary epithelial cells are capable of de novo biosynthesis of choline moiety. We propose to culture rat and human mammary epithelial cells on a matrix. We will characterize choline transport and metabolism, de novo biosynthesis of choline, as well as formation and secretion of milk fat globules and casein using this cell culture system. We will examine the changes that occur during differentiation of the cells, and during exposure to varying levels of prolactin, insulin hydrocortisone, progesterone, estradiol-17beta or oxytocin. We will also examine the effects of varying the availability of choline upon each of these parameters. In some tissues, carnitine transpor depends upon choline availability, we plan to determine whether this is tru in the mammary epithelial cell.
| Rohlfs, E M; Louie, D S; Zeisel, S H (1993) Lipid synthesis and secretion by primary cultures of rat mammary epithelial cells. J Cell Physiol 157:469-80 |
| Rohlfs, E M; Garner, S C; Mar, M H et al. (1993) Glycerophosphocholine and phosphocholine are the major choline metabolites in rat milk. J Nutr 123:1762-8 |
| Zhang, J; Blusztajn, J K; Zeisel, S H (1992) Measurement of the formation of betaine aldehyde and betaine in rat liver mitochondria by a high pressure liquid chromatography-radioenzymatic assay. Biochim Biophys Acta 1117:333-9 |
| Zeisel, S H (1992) Choline: an important nutrient in brain development, liver function and carcinogenesis. J Am Coll Nutr 11:473-81 |
