Endocrine Abstracts

Brown adipose tissue presently attracts broad interest due to the possibility that it may have the potential to counteract development of obesity and may have other positive metabolic effects, e.g. on glucose and lipid handling. As brown adipose tissue is found, to different extent, in nearly all humans up to middle age, the possibility to affect its activity may be of significance for human health. Brown adipose tissue is affected by several (neuro)endocrine factors. Best studied are the effects of the sympathetic nervous system; the released norepinephrine not only directly induces the thermogenic processes in the tissue but also promotes the differentiation process and, uniquely, also cell proliferation and anti-apoptosis. The interaction with thyroid hormone is not well understood. Apparently, the effects of centrally administered thyroid hormone on body metabolism are mediated via a stimulation of the sympathetic nervous system whereas the increased metabolic rate observed after peripheral thyroid hormone treatment is not dependent on brown fat thermogenic activity. At thermoneutrality, glucocorticoid treatment diminishes the thermogenic capacity of brown adipose tissue but the increased obesity observed during such treatment is not due to the inactivity of the tissue. There is no direct effect of leptin on brown adipose tissue activity but leptin increases body temperature if given to leptin-deficient mice; this is an effect directly on the apparent set point for the body temperature. The hormonal basis for the increased recruitment and activity of the tissue seen during so-called diet-induced thermogenesis is still not identified.