The generation of insulin-like growth factor-1--sensitive cells by growth hormone action.

Insulin-like growth factor-1 (IGF-1), a mitogenic polypeptide, is usually considered the sole effector by means of which growth hormone increases tissue mass. However, growth hormone, but not IGF-1, directly promotes the differentiation of cultured preadipocytes to adipocytes. Adipocytes newly differentiated from precursor cells in response to growth hormone were shown to be much more sensitive to the mitogenic effect of IGF-1 than the precursor cells. The result of IGF-1 action is therefore a selective multiplication of young differentiated cells (cloned expansion). This supports the concept of a dual effector system in which the preferred target cells of IGF-1 action are created by the direct action of growth hormone.