At present it is unknown whether these effects are due to direct effects of growth hormone on hematopoietic cells or if they are caused by the induction of insulin-like growth factor-1 (IGF-1) synthesis.n support of the second possibility, we have induced apoptosis of both nonadherent bone marrow cells and a myeloid progenitor cell line by depriving these cells of CSFs. Preliminary results indicate that addition of IGF-1 to these cells reduces apoptotic cell death by 50%.