Contribution of growth hormone to the adipogenic activity of serum

GH promotes the conversion of cultured preadipose 3T3 cells into adipose cells. The serum of most animals also promotes this differentiation. In order to determine the extent to which GH is responsible for the adipogenic activity of serum, we used a specific antiserum able to suppress completely the adipogenic activity of rat and bovine GH. This antiserum also suppressed all the adipogenic activity secreted into culture medium by a rat pituitary cell line as well as all the adipogenic activity of crude bovine pituitary extract. When tested against the adipogenic activity of serum, the antiserum to GH reduced the activity by one third to half. It is concluded that 1) GH in the concentration and form present in serum is an effective promoter of adipose differentiation, and 2) there exists in serum another adipogenic activity not immunochemically recognizable as GH. This activity is presumed to be of nonpituitary origin.