The story of adipose tissueas an endocrine organ begein with discovery of leptin in 1994.
Leptin is a hormonesecreted by adipose tissue and several physiologic functions including satiety viahypothalamic actions. The subsequent researches have identified many moreadipose tissue secreted prodicts like hormones, cytokines and so calledadipokines. A list of these adipose tissue secretd products is shown in Table1. The discovery of these adipose tissueproducts added a new dimension to physiologic role of adipose tissue in health.Adipose tissue can regulate food intake and energy expenditure by secretion ofthese chemical signals.
Therefore capable of orchestrating changes in energybalance and whole body nutritional status. Obesity is associated with bothqualitative as well as quantitative changes in adipose tissue. These pathologicchanges (so called adiposopathy or sick fat) along with its physiologic role inmetabolism have led to the reclassification of adipose tissue as an endocrineorgan. Like other endocrine organs, adipose tissue is composed of several celltypes, though adipocytes are the major constient of this organ. The additionalcell types present in its stroma-vascular fraction include pluripotent stemcells, cells commited to adipogenesis, macrophages (M1 to M2 spectrum),lymphocytes, monocytes, eocinophils, pericytes and endothelial cells etc.
Thesedifferent cell types play important role in adipose tissue physiology viaparacrine and endocrine actions including secretion of adipocytokines mentionedabove. The paracrine relationship between the adipocytes and infiltratingimmune cells regulate adipose tissue function including adipogenesis,inflammation FFA and adipocytokine flux, the mainstream of adipose tissuepatholophysiology. Apart from paracrine effects, adipose tissue-derived secretedfactors (i.
e. endocrine effects) can influence multiple biological systems of the body, whichinclude energy homeostasis (lipid and carbohydrate metabolism, appetite,thermogenesis), the immune system, reproductive function, hemostasia, bloodpressure, and angiogenesis etc. Some of the endocrine actions of the adiposetissue secretion are the the linksbetween obesity and clinical diseases, such as insulin resistance,hypertension, hyperlipidemia, type 2 diabetes, and coronary heart disease.
4
