PET Assessment of Brown Fat

摘要

Brown fat or brown adipose tissue (BAT) is an organ specific to mammals. The brown adipocyte is discerned from the white by having numerous fat vacuoles and a much higher number of iron-containing mitochondria creating the brown color. Brown fat is richly innervated by sympathetic nerves and is characterized by its unique protein, uncoupling protein-1 (UCPI)orthermoge-nin, which is essential for the function of brown fat: to convert food into heat. UCP1 uncouples mito-chondrial respiration from adenosine triphosphate (ATP) synthesis, thereby stimulating heat production at the expense of energy in the form of ATP ("nonshivering" thermogenesis). Brown fat plays a crucial function in maintaining normal body temperature in small rodents and in newborn infants.In human autopsy series from several decades ago, it was shown that brown fat was distributed widely across the body in the first decade, but disappeared from most areas with increased age only to persist around the kidneys, adrenal glands, aorta, and in the neck and mediastinum.