Endocrine Abstracts

The occurrence of obesity and the related metabolic syndrome increases dramatically worldwide. A positive energy balance causes obesity. Facultative thermogenesis, which is the increase in energy expenditure in response to cold or diet, may be an effective way to affect the energy balance.

Several studies have confirmed that humans show significant (mild) cold induced thermogenesis, i.e. without shivering. Tissues shown to be involved in adults are skeletal muscle and brown adipose tissue (BAT). The most likely cellular mechanism in both tissues is mitochondrial uncoupling. Recently functional BAT has been rediscovered in adult humans.

At the functional level, adipocytes can be subdivided into white and brown. The most important function of white adipocytes is energy storage, while the main function of brown adipocytes is heat production. Brown adipocytes are located in BAT or white adipose tissue, the latter is called ‘BRITE’ (brown-in-white).

From metabolic studies it is known that the facultative thermogenesis is blunted in obese humans, although there is a large individual variation. Intriguingly, functional and active BAT is also inversely correlated with body mass index (BMI) and body fat percentage in humans. An important aspect in the current studies is to find our whether BAT can be activated and recruited in obese subjects. Animal and human studies indicate that recruitment and activation of brown and brite adipocytes can potentially be accomplished by pharmacological, nutritional or environmental intervention. Crucial in the activation of adaptive thermogenesis and brown adipocytes are the sympathetic nervous system and the thyroid hormone axis.

Finally, thermogenic BAT is a major site for lipid breakdown and glucose uptake, and thus the thermogenic capacity of even small amounts of brown adipocytes has emerged as an attractive target for anti-diabesity therapies.

Results will be given from studies on BAT activity in lean, obese and morbid obese subjects before and after weight reduction.