ABSTRACT
Brown adipocytes represent a unique type of cell by virtue of their content of a specific uncoupling protein (UCP-1). Indeed, the presence of UCP-1 defines an adipocyte as brown (Himms-Hagen and Ricquier, 1998). This protein, which is not found in any other mammalian cell, has a key role in the production of heat (thermogenesis) in the body. In experimental animals, this role has been shown to be important in the maintenance of body temperature in a cold environment, and in the maintenance of energy balance. Thermogenesis in brown adipocytes is brought into play by impulses from the central nervous system reaching the adipocytes via sympathetic nerves. The nervous stimuli arriving at the brown adipocytes release noradrenaline which, by reacting with adrenergic receptors on the cell surface, initiates the adipocytes’ thermogenic response. Prolonged sympathetic stimulation can also induce hyperplasia of the brown adipocytes, with proliferation of their mitochondria, and thereby lead to hypertrophy of the brown adipose tissue (BAT). In most species, the principal adrenergic receptor of brown adipocytes is the ß3-adrenoreceptor (ß3AR). This receptor is not, however, unique to brown adipocytes but is also present in white adipocytes.
