An adipogenic serum factor in genetically obese rodents.

The adipose conversion of 3T3-Li cells depends on a serum factor present in high amounts in fetal calf serum, which is heat stable and can be extracted from serum by ethanol precipitation. Sera of two genetically obese rodent species, fa/fa Zucker rats and C57Bl/KsJ-db/db mice, contain a high adipogenic activity which is very similar to that found in fetal calf serum. In contrast, sera of their lean siblings (Fa/Fa-Zucker rats and C57Bl/KsJ-+/+ mice) are devoid of adipogenic activity.