Mammary gland lipids

Tanioka, H., Lin, C. Y., Smith, S. and Abraham, S. 1974. Acyl specificity in glyceride synthesis by lactating rat mammary gland. Lipids 9, 229-234. 

Ellis, L.A., Hamosh, M. 1992. Bile salt stimulated lipase comparative studies in ferret milk and lactating mammary gland. Lipids 27, 917-922. 

The perturbation of the incorporation of linoleic add metabolites into mammary gland lipids by CLA metabolism may lead to the hypothesis that CLA is able to create a mild arachidonic acid deficiency condition, in particular in the mammary tissue which is composed mainly of neutral lipids. In fact, because CLA and some of its metabolites are preferentially incorporated into neutral lipids (15), unlike linoleic acid, which is instead incorporated mainly into phospholipids, the preponderance of neutral lipids in the mammary tissue renders the competition between these two fatty acids more favorable toward CLA. It has been demonstrated that mammary tumorigenesis requires essential fatty acids, and eicosanoid inhibitors are able to reduce tumor incidence in experimental models (22). CLA, likely by decreasing the supply of arachidonic acid and inhibiting eicosanoid formation through its metabolites, may counteract arachidonic acid-derived eicosanoid action. Because the decrease of arachidonic acid, CLA metabolite incorporation, TEB density, and tumor incidence correlated with the (XA dietary intake, we can speculate that TEB density could also be modulated by eicosanoids. More data are required, however, to substantiate this hypothesis and to identify which eicosanoid(s) may be responsible for such effects. 

There are striking similarities in the mechanisms of formation of chylomicrons by intestinal cells and of VLDL by hepatic parenchymal cells (Figure 25—2), perhaps because—apart from the mammary gland—the intestine and liver are the only tissues from which particulate lipid is secreted. Newly secreted or nascent chylomicrons and VLDL contain only a small amount of apolipoproteins C and E, and the frill complement is acquired from HDL in the circulation (Figures 25—3 and 25-4). Apo B is essential for chylomicron and VLDL formation. In abetalipoproteinemia (a rare disease), lipoproteins containing apo B are not formed and lipid droplets accumulate in the intestine and liver. 

Moore, J. H. and Christie, W. W. (1981) Lipid metabolism in the mammary gland of ruminant animals In Progress in Lipid Research Supplement no. 1 (Ed. Christie, W. W.), Pergamon Press, London, pp. 227 276. 

Emulsions are mixture of two (or more) immiscible substances. Everyday common examples are milk, butter (fats, water, salts), margarine, mayonnaise, skin creams, and others. In butter and margarine, the continuous phase consists of lipids. These lipids surround the water droplets (water-in-oil emulsion). All technical emulsions are prepared by some kind of mechanical agitation or mixing. Remarkably, the natural product, milk, is made by organisms without any agitation inside the mammary glands. 

The principal constituents (lactose, lipids and most proteins) of milk are synthesized in the mammary gland from constituents absorbed from blood. However, considerable modification of constituents occurs in the mammary gland the constituents are absorbed from blood through the basal membrane, modified (if necessary) and synthesized into the finished molecule (lactose, triglycerides, proteins) within the mammocyte (mainly in the endoplasmic reticulum) and excreted from the mammocyte through the apical membrane into the lumen of the alveolus. 

Droplets of different density and lipid protein ratios ranging from about 1.5 1 to 40 1 have been isolated from bovine mammary gland. Triglycerides are the major lipid class in droplets of all sizes and represent increasingly greater proportions of total droplet mass in increasingly less dense droplet preparations. Surface coat material of droplets contains cholesterol and the major phospholipid classes found in milk, i.e. sphingomyelin, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and phosphatidyl-serine. 

Rao, G. A. and Abraham, S. 1975. Stimulatory effect of glucose upon triglyceride synthesis from acetate, decanoate, and palmitate by mammary gland slices from lac-tating mice. Lipids 10, 409-412. 

Patton, S. and Jensen, R. G. 1975. Lipid metabolism and membrane functions of the mammary gland. In Progress in the Chemistry of Fats and Other Lipids. R. G. Holman (Editor). Pergamon Press, Oxford, pp. 163-277. 

Keenan, T. W. and Huang, C. M. 1972B. Membranes of mammary gland. VI. Lipid and protein composition of Golgi apparatus and rough endoplasmic reticulum from bovine mammary gland. J. Dairy Sci. 55, 1586-1596. 

Montesano, R., Ravazzola, M. and Orci, L. 1983. Filipin labelling of lipid droplets in lactating rat mammary gland. Cell Biol Intern Rep. 7, 194. 

Stein, 0. and Stein, Y. 1967. Lipid synthesis, intracellular transport, and secretion. II. Electron microscopic radioautographic study of the mouse lactating mammary gland. J. Cell Biol. 34, 251-263. 

Chylomicrons transport dietary triacylglycerol and cholesteryl ester from the intestine to other tissues in the body. Very-low-density lipoprotein functions in a manner similar to the transport of endogenously made lipid from the liver to other tissues. These two types of triacylglycerol-rich particles are initially degraded by the action of lipoprotein lipase, an extracellular enzyme that is most active within the capillaries of adipose tissue, cardiac and skeletal muscle, and the lactating mammary gland. Lipoprotein lipase catalyzes the hydrolysis of triacylglycerols (see fig. 18.3). The enzyme is specifically activated by apoprotein C-II, which... 

Much of my previous research experience had been in lipid biochemistry and DMBA, a polycyclic hydrocarbon, is essentially a lipid xenobiotic. The suggestion had been made by Dao et al O) that the specific induction of mammary tumors by DMBA and other polycyclic hydrocarbons might be due to their tendency, as lipids, to accumulate and persist in the adipose tissue of the mammary gland, thereby increasing the exposure to the susceptible mammary epithelial tissue. If this were indeed a factor in the ability of these compounds to produce mammary tumors, it seemed to us that it might be possible to influence their effectiveness by altering fat metabolism in the body. 

Badawi, A.F. and Archer, M.C., Effect of hormonal status on the expression of the cyclooxygenase 1 and 2 genes and prostaglandin synthesis in rat mammary glands, Prostaglandins. Other Lipid Medial,... 

Milk composition is not constant and is influenced by the timing of feeding and duration of nursing postpartum. Human milk contains about 2-3% fat and a large number of proteins. The pH of milk tends to be lower than that of plasma. Most water-soluble substances are excreted into the milk by simple diffusion, and lipid-soluble compounds are transported along with lipid molecules from plasma into the mammary gland. The amount of a certain substance transferred to the milk depends on the physicochemical properties of the... 

The fatty acids of bovine milk fat arise from two sources synthesis de novo in the mammary glands and the plasma lipids originating from the feed. The fatty acids from these two sources differ in their structure. The fatty acids that are synthesised de novo are short-chain and medium-chain length acids, from 4 0 to 14 0 and also some 16 0, while the Cis fatty acids and some 16 0 arise from the plasma lipids. De novo fatty acid synthesis accounts for approximately 45% (w/w) of the total fatty acids in milk fat, while lipids of dietary origin account for the rest (Moore and Christie, 1979). 

The net result of these processes is that the fatty acids in the mammary gland, which originate from the dietary lipids, consist of substantial quantities of 16 0, 18 0 and oleic acid, small amounts of linoleic and linolenic acids, and limited quantities of other monoenoic and dienoic fatty acids such as llt-18 l and 9c, llt-18 2. 

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