The autonomic nervous system, adipose tissue plasticity, and energy balance

In most mammals, two types of adipose tissue, white and brown, are present. Both are able to store energy in the form of triacylglycerols and to hydro lyze them into free fatty acids and glycerol. Whereas white adipose tissue can provide lipids as substrates for other tissues according to the needs o f the organism, brown adipose tissue will use fatty acids for heat producti on. Over the long term, white fat mass reflects the net balance between ene rgy expenditure and energy intake. Even though these two parameters are hig hly variable during the life of an individual, most adult subjects remain r elatively constant in body weight throughout their lives. This observation suggests that appetite, energy expenditure, and basal metabolic rate are li nked. An important characteristic of the adipose tissue is its enormous pla sticity for volume and cell-number variations and an apparent change in phe notype between the brown and white adipose tissues. The present review focu ses on the cellular mechanisms participating in the plasticity of adipose t issues and their regulation by the autonomic nervous system. There is compe lling evidence with regard to the importance of the nervous system in the r egulation of adipose tissue mass, either brown or white, by acting on the m etabolic pathways and on the plasticity (proliferation, differentiation, tr ansdifferentiation, apoptosis) of these tissues. A better comprehension of the different mechanisms involved in the feedback loop linking the brain an d these two types of adipose tissue will lead to a better understanding of the pathophysiology of various disorders including obesity, cachexia, anore xia, and type II: diabetes mellitus. Nutrition 2000;16:903-908. (C) Elsevie r Science Inc. 2000.