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G. Flik, ZigZAGging through Fat Stores, The Journal of Clinical Endocrinology & Metabolism, Volume 94, Issue 12, 1 December 2009, Pages 4668–4670, https://doi.org/10.1210/jc.2009-2199
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Extract
When reading how in the 1950s and 1960s Bürgi and Schmid (1) at Harvard purified and isolated from human blood plasma a glycoprotein by zinc precipitation, which is now best known as Zn-α2-glycoprotein (ZAG), one can only wonder about the complete and detailed biochemical approach and pure marvel of biochemistry at that time. In the present-day world of ZAG, this seminal paper deserves a status similar, for instance, to that of the work of Lowry and colleagues on protein determination (reviewed in Ref. 2). What Bürgi and Schmid did not know, nor could they anticipate, was the role played by “their” glycoprotein in endocrinology and metabolism. At that time, discussions still concerned questions such as whether a cell could produce only one hormone or maybe more. Hormones came from designated glands such as the pituitary gland, the endocrine pancreas, or adrenals. Tissues and organs, such as the skin, heart, liver, and kidney, were only later revealed as sources of endocrine signals. Now, almost 50 yr later, production of multiple signals by a single cell type is the rule rather than the exception, and the notion that tissues other than the classical endocrine glands, tissue such as liver and adipose, are endocrine tissues is established. Because many signals in our body serve functions beyond the classical endocrine function, viz. as intracrines, autocrines, and paracrines, we should be alert to the possibility of finding signals in body fluids other than blood plasma and not be prejudiced with regards to function because of exotic appearances of as yet poorly-defined signal substances. Such a notion would certainly apply to adipose tissue as an endocrine tissue and the complex web of adipo(cyto)kines produced by fat and liver cells involved in regulation of our energy stores and communication between these stores, other peripheral tissues of mesenchymal origin such as bone, or the immune system, and the central nervous system (3, 4).
