CELLULAR STRUCTURE AND FUNCTION OF RAT FAT-CELLS IN THE PRIMARY CULTURE

A primary culture of undigested fat tissue fragments was used to obtai n fat cells in vitro. On day 2 of culture, immature fat cells, which a re fibroblast-like fat cells containing fine lipid droplets, appeared, surrounding the fat tissue fragments, and began to proliferate extens ively. Afterwards, these fibroblast-like fat cells grew to become mult ilocular fat cells containing larger intracytoplasmic lipid droplets, and differentiated further into unilocular fat cells containing a sing le large intracytoplasmic lipid droplet. Treatment with dibutyryl-cAMP , which is a second messenger of the lipolytic factor, caused the cult ured fat cells to retract, and the intracytoplasmic lipid droplets of those fat cells became finely granulated and decreased along with an i ncrease of hormone-sensitive lipase activities. Conversely, administra tion of insulin caused the lipid droplets in the fat cells to increase and become larger along with an increase of alpha-glycerophosphate de hydrogenase activities. These findings indicate the occurrence of lipo lysis and lipogenesis of fat cells in vitro. Immuno-cytochemistry reve aled that vimentin surrounded intracytoplasmic lipid droplets, and bec ame distinct with an increase of lipid droplets through lipogenesis in the fat cells. Vimentin seems to be correlated to the behavior of lip id droplets in the fat cells. Fat cells in this study showed the appro priate cellular structures and functions in response to stimulation of lipolysis and lipogenesis under culture conditions. It is expected th at in vitro culture of fat cells will facilitate cell biological eluci dation of obesity in the future.