Adipose tissue cells

Norepinephrine secreted at sympathetic nerve endings binds to y8-adrenergic receptors on brown adipose tissue cells and initiates cAMP-dependent triacylglycerol lipase... 

Moreover, further study by Sheldon et al. (1962) has shown that the vesicles in the (jytoplasm of adipose tissue cells represent cross sections through a tuluilar membranous component of the cytoplasm which has... 

Fig. 2. Acylglycerols. Biosynthesis of triacylglycer-ols in liver and adipose tissue cells. EC 1.1.1.8 Glycerol-3-phosphate dehydrogenase (NAD "). EC 2.3.1.15 (j ycerol-3-phosphate acyltransferase. EC 2.3.1.20 Diacylglycerol acyltransferase. EC 2.3.1.51 1-AcylgIycerol-3-phosphate acyltransferase. EC 3.1.3.4 Phosphatidate phosphatase. EC 6.2.1.3 Long-chaln-fatty acid-CoA ligase.

Effect of Insulin and Diabetes on Adipose Tissue. For a long time, the role of adipose tissue in metabolism was underestimated. It is now clear that the adipose tissue cell is more than a site of lipid storage. It is also an actively metabolizing cell—performing lipid synthesis and breakdown—with well-developed... 

Azain, M.J., Hausman, D.B., Sisk, M.B., Flatt, W.P., and Jewell, D.E. 2000. Dietary conjugated linoleic acid reduces rat adipose tissue cell size rather than cell number. Journal of Nutrition 130, 1548-1554. 

These findings make it probable that disruption and resynthesis of the ester bonds play a role at some phase of the facilitated transport of triglycerides into the adipose tissue cells. It is, however, not yet settled where these processes take place. Lipoprotein lipase has been implicated in this process. A lipoprotein lipase, similar to that appearing in blood following heparin injection, has been extracted from adipose tissue (Korn 1955 a) and is released into the medium when adipose tissue is incubated in a solution containing heparin (Hollenberg 1959 Cherkes and Gordon 1959 Robinson 1960). 

In contrast to oil from plant tissue, the recovery of animal fat is not restricted by rigid cell walls or sclerenchyma supporting tissue. Only heating is needed to release fat from adipose tissue (dry or wet rendering with hot water or steam). The fat expands when heated, tearing the adipose tissue cell membrane and flowing freely. Further fat separation is simple and does not pose a technical problem (Fig. 14.1). 

Activation of intracellular hormone-sensitive lipase. This catalyses the hydrolysis of the triacylglycerol stored in adipose tissue cells, leading to release into the bloodstream of free fatty acids (which are transported bound to albumin) and glycerol, which is an important substrate for gluconeogenesis in the liver. 

Although it would be desirable to measure sugar transport in isolated adipose tissue cells as well as in intact epididymal fat pads we have so far been unable to make satisfactory measurements of galactose space in the isolated cells. We have instead used the incorporation of radioactivity from glucose-U-into CQ2 and lipid as an indication of glucose transport. 

Free fatty acids (FFA) and glycerol are released from adipose tissue following the action of a hormone-sensitive lipase which hydrolyses triglycerides (TG). This lipase is activated by a variety of hormones, notably catecholamines, ACTH, TSH and glucagon These hormones, when added to incubated adipose tissue preparations. induce a prompt accumulation of glycerol into the medium, of FFA in the medium (when albumin is present) and in adipose tissue cells. 

Metaraminol is almost devoid of lipolytic activity and it acts therefore as a powerful inhibitor of FFA mobilization The well-known observation that insulin can decrease the release of FFA and glycerol from adipose tissue in vitro, even in the absence of glucose and lipolytic hormones, has prompted investigators to see whether drugs known to lower blood glucose such as sulphonylureas have a similar activity. In isolated adipose tissue cells, sulphonylmeas (tolbutamide, tolazamide) decrease the rate of FFA release in a way similar to that of insulin. This effect is not mediated by insulin because it is still present when anti-insulin is added and it seems to be a direct effect, possibly at the level of adenyl cyclase activation. Accordingly, the intravenous injection of tolbutamide in man reduces plasma FFA levels. 

Cuatrecasas, P., 1971a, Insulin-receptor interactions in adipose tissue cells Direct measurement and properties, Proc. Natl. Acad. Sci. USA 68 1264. 

Cuatrecasas, P., and Illiano, G., 1971, Membrane sialic acid and the mechanism of insulin action in adipose tissue cells, J. Biol. Chem. 246 4938. 

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