Insulin storage/secretion

Zn occurs in enzymes that realize the synthesis and the metabolism of DNA and RNA [45] it influences the metabolism and the synthesis of proteins [5] it participates in glycolysis and neoglucogenesis and also in prostaglandin synthesis and cholesterol metabolism it prevents lipid peroxidation and maintains membrane structures [46], Other roles of zinc [5,47] include its effect on the storage, secretion, polymerization, and receptive fixation of insulin [5,47,48] it influences the biosynthesis of ACTH [5,47] it occurs in biologically active proteins such as growth factor [47] or gustin [49]. 

Insulin is secreted by the pancreatic P-cells and is required for the S5mthesis of the glucose storage polymer glycogen and is also required for the entry of glucose into tissues. Reduced glucose entry into tissues is the major effect of insulin deficiency and this produces an increased level of... 

Ascorbate can also serve as a signal. In cultured cells, which are usually deficient in vitamin C, addition of ascorbate causes an enhanced response to added iron, inducing synthesis of the iron storage protein ferritin.11 Ascorbate indirectly stimulates transcription of procollagen genes 1 and decreases secretion of insulin by the pancreas.)) However, since its concentration in blood is quite constant this effect is not likely to cause a problem for a person taking an excess of vitamin C. 

CM and VLDL secreted by intestinal cells and VLDL synthesized and secreted in the liver have similar metabolic fates. After secretion into the blood, newly formed CM and VLDL take up apoprotein (apo-C) from HDL and are subsequently removed from the blood (plasma half-life of less than 1 h in humans [137]) primarily by the action of lipoprotein lipase (LPL). Lipoprotein lipase is situated mainly in the vascular bed of the heart, skeletal muscle, and adipose tissue and catalyzes the breakdown of core TG to monoglycerides and free fatty acids, which are taken up into adjacent cells or recirculated in blood bound to albumin. The activity of LPL in the heart and skeletal muscle is inversely correlated with its activity in adipose tissue and is regulated by various hormones. Thus, in the fasted state, TG in CM and VLDL is preferentially delivered to the heart and skeletal muscle under the influence of adrenaline and glucagon, whereas in the fed state, insulin enhances LPL activity in adipose tissue, resulting in preferential uptake of TG into adipose tissue for storage as fat. 

Fig. 21.2 Major effects of AMPK activation on numerous tissues. AMPK plays a key role in regulating whole body energy storage and expenditure. In hypothalamus, AMPK is involved in regulation of satiety and food intake. Activation of AMPK in the hypothalamus increases food intake, whereas inhibition decreases intake. In peripheral tissues such as skeletal muscle and liver, activation of AMPK increases energy expenditure by stimulating mitochondrial genesis and energy substrate utilization. AMPK also regulates lipolysis in adipose tissue and insulin secretion in pancreas.

The storage of triacylglycerols in adipose tissue is mediated by insulin, which stimulates adipose cells to secrete lipoprotein lipase and to take up glucose, the source of glycerol for triacylglycerol synthesis. 

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