Thermogenesis in XXXX brown adipose tissue and skeletal muscle induced by sympathomimetic stimulation.

@entity1 @entity6358 @entity28 @entity235 @entity1373 @entity26 @entity35
The aim of the present work was to elucidate the importance of brown adipose tissue (BAT) and skeletal muscle for @entity6358 -induced thermogenesis, and to examine the effect of chronic @entity6358 treatment on energy expenditure. The investigations were carried out in vivo on @entity1 , as well as on @entity35 and @entity235 . In rodents BAT is the major site of cold-induced nonshivering thermogenesis and of facultative thermogenesis: the component of food-induced thermogenesis storage of nutrients. BAT thermogenesis is mediated through an activation of the sympathetic nervous system. Via a sustained stimulation of the sympathetic nervous system, acclimation to cold and overfeeding induces @entity1373 of BAT, and subsequently an increased thermogenic capacity. In a number of @entity28 syndromes in rodents the sympathetic mediation is defective, and this leads to extreme sensitivity to cold and to @entity28 . BAT has been reported to be present also in @entity1 , and there has been focused mainly on the interscapular subcutaneous tissue. An @entity6358 -induced increase of the interscapular skin temperature has been interpreted as evidence of the presence of thermogenic BAT. This lead to the assumption that BAT, also in @entity1 , plays a significant role in the regulation of energy balance. Likewise, the hypothesis has been advanced that a diminished thermogenesis in BAT may be the cause of some types of @entity1 @entity28 . After validation of the xenon clearance method in @entity35 for blood flow measurements in BAT, the method was applied on @entity1 to examine the @entity6358 -induced increase in the interscapular temperature. The warmest interscapular skin area was localized by thermography during @entity6358 stimulation. In a second study subcutaneous blood flow and temperature were measured in this area during @entity6358 stimulation and compared to the response of white adipose tissue in the lumbar area. The results showed that the increases in blood flow and temperatures were of similar magnitude in the two locations. Biopsies taken from the warmest interscapular spots did not contain brown adipocytes. A histological study on @entity1 autopsies confirmed that BAT is rare in the interscapular tissue, but frequently occurring in the perirenal depot. In the next study, the thermogenic function of the perirenal BAT was examined by measurements of blood flow and local temperature. Perirenal BAT thermogenesis was uninfluenced by @entity6358 in 4 of 5 subjects. It was estimated that BAT thermogenesis in the single responding subject could account for maximally 15% of the @entity6358 -induced increase in whole body @entity26 consumption.(ABSTRACT TRUNCATED AT 400 WORDS)
