PHYSIOLOGICAL APPROACH TO MATURATION OF BROWN ADIPOCYTES IN PRIMARY-CELL CULTURE

Molecular and metabolic aspects of differentiation of brown adipocytes of the Djungarian hamster (Phodopus sungorus) were studied in primary culture. Expression of uncoupling protein and lipoprotein lipase were investigated by Western and Northern blotting and indirect immune-flu orescence microscopy. The activity of 5'-deiodinase type II was determ ined by a radioactive enzyme assay. Activity of cytochrome-c-oxidase a nd cell respiration rates were measured with a Clark electrode. We eva luated functional differences of developmental stages by measuring the reaction to beta-adrenergic stimulation throughout the differentiatio n process. The results show that differentiation of hamster brown adip ocytes is an at least two-step development with physiologically discri minable cell types. Generation of triiodothyronine (T3) from thyroxine by activation of the 5'deiodinase occurs in immature brown adipocytes and is mediated primarily by beta 1- rather than beta 3-adrenergic re ceptors. The thermogenic capacity is subsequently increased in mature brown adipocytes. beta-Adrenergic receptor stimulation increases UCP e xpression of mature adipocytes but is not able to recruit new brown ad ipocytes. (C) 1997 Elsevier Science B.V.