SIGNAL-TRANSDUCTION IN BROWN ADIPOSE-TISSUE RECRUITMENT - NORADRENALINE AND BEYOND

The classical effect of noradrenaline on brown adipose tissue is stimu lation of heat production, However, it is likely that noradrenaline is also the major regulator of proliferation and differentiation, The ad renergic receptors involved include at least beta(1), beta(3), alpha(2 ), and alpha(1). Heat production is mainly stimulated via beta(3) rece ptors and cAMP. Cell proliferation is mainly stimulated via beta(1) re ceptors and cAMP. Cell differentiation is also adrenergically promoted : at least the expression of the gene for the tissue-specific uncoupli ng protein thermogenin is controlled via B, receptors and cAMP, There is a switch in beta-receptor endowment between young (B,) and mature ( B,) cells. The expression of several transcription factors is also und er adrenergic control: c-Fos gene expression depends synergistically o n beta- and alpha(1), stimulation, mediated via cAMP and [Ca2+](i), in creases. C/EBP beta gene expression is regulated only via beta-recepto rs, but the expression of the C/EBP alpha gene shows a switch during d ifferentiation: in young cells, the expression is repressed through bo th beta- and alpha(1)-receptors; in mature cells, the expression is st imulated via beta-receptors. It is likely that noradrenaline exerts it s proliferation- and differentiation-promoting action through alterati ons in the expression of these or other transcription factors.