Adipogenic activity in human plasma. Effects of feeding state and obesity

The potential of plasma from obese and non-obese subjects to stimulate the formation of new adipocytes was studied by assays in rat adipose precursor cells in primary culture. Adipogenic activity was followed in terms of rate of lipid filling, analysed by determination of triglyceride contents per unit protein, stimulation of multiplication, measured as rate of incorporation of labelled thymidine into DNA, and stimulation of differentiation, followed as an increase in glycerophosphate dehydrogenase activity. Plasma from obese subjects contained an excess of activity stimulating lipid filling, closely associated to the recent body weight histories with increased activity with a recent increase of body weight and vice versa. There was also a strong association with plasma concentration of triglyceride. The importance of the latter was demonstrated by acute feeding experiments with triglyceride, as well as by addition of isolated very-low-density lipoprotein and chylomicron fractions which caused increases of lipid filling activity closely in parallel to triglyceride contents of the culture medium. Specific stimulatory properties of plasma from weight-increasing obese subjects on adipose precursor cell multiplication and differentiation were not found. It was suggested that human obesity with an increased number of adipocytes is not characterized by elevated circulating specific stimulatory factors of new fat cell formation. Such factors are present in excess in both non-obese and obese subjects. It was hypothesized that the elevated lipid filling capacity in obese subjects might modify local inhibitory factors of adipocyte formation.