White adipose tissue is the major energy source in animals and humans. A very large part (95%) of total body triacylglycerols (TAG) is located in fat stores and TAG are central metabolic substrates. Adipose tissue makes a major contribution to the regulation of lipid metabolism, as it is a site of clearance of postprandial lipaemia through the action of lipoprotein lipase (EC 3.1.1.34; LPL) on chylomicron TAG and an important site of lipolysis where TAG are hydrolysed intracellularly by the hormone-sensitive lipase (EC 3.1.1.3; HSL), so named because of its responsiveness to catecholamines and insulin. In the post-absorptive state, this enzyme controlling fat cell lipolysis plays a determinant role in whole-body lipid-fuel availability. The mobilization of white-fat-cell TAG provides the body with a vital supply of fuel in the form of fatty acids (FA) and of gluconeogenic precursors in the form of glycerol. Adipose tissue is the major site of production of non-esterified FA (NEFA) and largely determines the plasma NEFA levels. NEFA have been recognized as the main energy source during starvation, various stressful situations (cold exposure, burn injury, surgical trauma etc.), as well as during exercise (Coppack et al. 1994). Plasma NEFA also represent a major source of energy in post-absorptive states because of their high energy content. Some organs such as the heart utilize NEFA almost exclusively to reach their metabolic requirements. FA are also precursors of essential organic molecules (e.g.prostaglandins, leukotrienes and thromboxane) and appear to be involved in the control of gene expression, cell proliferation and immune responses.
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