Lactating mammary glands

Figure 20-6. Pathway of conversion of (A) galactose to glucose in the liver and (B) glucose to lactose in the lactating mammary gland.

Wilson E, Butcher EC. CCL28 controls immunoglobulin (Ig)A plasma cell accumulation in the lactating mammary gland and IgA antibody transfer to the neonate. J Exp Med 2004 200 805-809. 

Triacylglycerol (i) chylomicrons (ii) very low density lipoproteins intestine (diet) liver adipose tissue, muscle, lactating mammary gland... 

Figure 7.3 The action of lipoprotein lipase in the hydrolysis of triacylglycerol in the blood and the fate of the fatty adds produced. Lipoprotein Lipase is attached to the luminal surface of the capillaries in the tissues that are responsible for removal of triacylglycerol from the bloodstream (e.g. adipose tissue, muscle, lactating mammary gland).

Aerobic muscle Lactating Mammary gland Heart... 

All three enzymes are present at high activities in the liver and in the lactating mammary glands. 

The most active organs in fatty acid synthesis are the liver and the lactating mammary gland. 

Oxytocin (Pitocin, Syntocinon) causes milk release (letdown) by stimulating contraction of the myoepithelial cells of the milk ducts in lactating mammary glands this forces milk from the alveoli of the breast. Oxytocin release is stimulated by suckling and by auditory and visual stimuli, such as a baby s cry. Oxytocin is available as a nasal spray, which is used as an aid to lactation when milk ejection is impaired. 

The oxidative portion of the pentose phosphate pathway consists of three reactions that lead to the formation of ribulose 5-phosphate, C02, and two molecules of NADPH for each molecule of glucose 6-phosphate oxidized (Figure 13.2). This portion of the pathway is particularly important in the liver and lactating mammary glands, which are active in the biosynthesis of fatty acids, in the adrenal cortex, which is active in the NADPH-dependent synthesis of steroids, and in erythrocytes, which require NADPH to keep glutathione reduced. 

PA is the precursor of many other phosphoglycerides. The steps in its synthesis from glycerol phosphate and two fatty acyl CoAs were illustrated in Figure 16.14, p. 187, in which PA is shown as a precursor of triacylglycerol. [Note Essentially all cells except mature ery-. throcytes can synthesize phospholipids, whereas triacylglycerol synthesis occurs essentially only in liver, adipose tissue, lactating mammary glands, and intestinal mucosal cells.]... 

Most fatty acids are synthesized in the liver following a meal containing excess carbohydrate and protein. Fatty acids are also synthesized in lactating mammary glands and, to a lesser extent, in adipose and kidney. 

Jarasch, E. D., Bruder, G., Keenan, T. W. and Franke, W. W. 1977. Redox constituents in milk fat globule membranes and rough endoplasmic reticulum from lactating mammary gland. J. Cell Biol. 73, 223-241. 

Nemanic, M. K. and Pitelka, D. R. 1971. A scanning electron microscope study of the lactating mammary gland. J. Cell Biol. 48, 410-415. 

Sasaki, M., Eigel, W. N. and Keenan, T. W. 1978. Lactose and major milk proteins are present in secretory vesicle-rich fractions from lactating mammary gland. Proc. Natl. Acad. Sci. USA 75, 5020-5024. 

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... 

Although there are many gaps in our knowledge of the synthesis and secretion of milk proteins by the lactating mammary gland, the essential features at the cellular level bear a close resemblance to pathways identified in many other eukaryotes (Mercier and Gaye, 1983 Kelly, 1985 Keenan and Dylewski, 1985). 

Uptake of Non-Lipid Metabolites by Lactating Mammary Glands... 

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