Endocrine regulation of uncoupling proteins and energy expenditure

Regulatory thermogenesis occurs upon exposure to the cold or during food in take. Among a variety of mechanisms leading to heat production, uncoupling of respiration in brown adipocyte mitochondria appears to be a major contri butor to resistance to the cold in rodents. This uncoupling mechanism is du e to the activity of uncoupling protein-1 (UCP-1), a specific carrier prese nt in the inner membrane of mitochondria. The recent identification of UCP- 2 and UCP-3, two homologues of the brown fat UCP, suggested that respiratio n uncoupling could contribute to thermogenesis in most tissues. Activity an d expression of the three UCP's are stimulated by several neuromediators an d hormones such as noradrenaline, tri-iodothyronine and leptin.