Recently, there has been rapidly growing interest in cell culture models that allow the study of the adipose differentiation process in vitro, as well as the long-term regulation of fat cell metabolism in human adipose tissue (AT) material. Although valuable clonal preadipocyte cell lines of rodent origin have been available for more than 20 yr, it became more and more obvious from subsequent studies that substantial differences exist in the developmental stage and regulation of differentiation, as well as in specific adipocyte functions, between rodent and human AT (1 –3 ). This knowledge makes it necessary to use human cell culture models, if specific questions concerning human AT metabolism and the mechanisms that may lead to either hypertrophic or hyperplastic growth in humans are investigated. Another aspect that is currently attracting considerable attention is the secretory function of adipocyte precursors and fat cells. Numerous factors are released from these cells, and maintain an intense crosstalk with distant organs, or act at the local level (4 ).
