Adipogenic factors in human serum promote the adipose conversion of 3T3-L1 fibroblasts.

The adipose conversion of 3T3-L1 fibroblasts to fully developed adipocytes depends on the presence of serum in the culture medium. This study demonstrates that human serum or plasma also effectively promote the adipose conversion of 3T3-L1 cells. At rising serum concentrations this effect is abolished however by the presence of antiadipogenic factors. Sera of newborns contained the highest adipogenic activity, approximately 1.8-fold higher than sera from lean adults. This difference is probably due to higher growth hormone (GH) concentrations. Adipogenic activity in sera from obese adults under reduction diet and in sera from older persons did not differ from that found in sera from lean young adults. Complete elimination of GH was achieved by heat treatment and ethanol precipitation. About 40-60 percent of the adipogenic activity in serum samples from adults and more than 70 percent of the activity in sera from newborns is due to GH. The remaining adipogenic activity was partially purified by gel chromatography at acidic pH. We conclude from these results that human serum contains at least two adipogenic factors: GH and a heat- and acid-stable low-molecular-weight component.