Lipolysis and lipogenesis from glucose in human fat cells of different sizes. Effects of insulin, epinephrine, and theophylline.
Lipogenesis from glucose and lipolysis in human omental and subcutaneous fat cells were studied as functions of adipose cell size and number in adult females. Since subcutaneous fat cells were larger than those prepared from the greater omentum, a comparison could be made of the metabolism of different sizes of cells within individual subjects. Rates per cell of glyceride-glycerol and glyceride-fatty acid synthesis from glucose were similar in omental and subcutaneous fat cells incubated in the presence or absence of insulin. However, subcutaneous fat cells exhibited higher rates of basal lipolysis than omental fat cells and these differences were maintained when lipolysis was stimulated with theophylline. Different rates of lipolysis were not demonstrable after incubations with epinephrine, indicating that subcutaneous fat cells were less responsive to this hormone than smaller omental fat cells. Correlation and partial correlation analysis showed that differences in basal and theophylline-stimulated lipolysis between fat cells prepared from different subjects and between omental and subcutaneous fat cells could be accounted for by differences in adipose cell volume. In subcutaneous fat cells highly significant intercorrelations were demonstrated between cell volume, basal lipolysis, and the basal conversion of glucose to glyceride-glycerol. There was no correlation between fat cell volume, age, or relative obesity and the effects of theophylline or insulin on lipolysis or lipogenesis from glucose in vitro when the data were expressed as percentage changes above basal values.