Leptin and the adipocyte endocrine system.

Although adipose tissue has long been considered to be metabolically passive and primarily responsible for energy storage, recent scientific advances have dramatically altered our understanding of the function of this ubiquitous tissue. The fat cell is a transducer of energy supply for the changing metabolic needs of the body, modulating glucose homeostasis, hypothalamic function, sympathetic output, vascular tone, immune response, and reproduction. Through endocrine/autocrine and paracrine actions, adipocyte-derived molecules defend the body during periods of energy deficit and stress. With the development of obesity, maladaptive responses to adipose excess result in pathologic states of inflammation, coagulopathy, and altered insulin sensitivity.