Induction of sensitivity of fibroblast cultures to pituitary growth hormone by a thermostable serum factor

This paper presents data to show that highly purified pituitary growth hormone (GH) preparations, themselves unable to stimulate DNA biosynthesis in cultures of adult human skin fibroblasts, acquire this ability if the cells are treated simultaneously with a factor present in a thermostable and acid-resistant fraction of rat blood serum. Activity of this factor in rat blood serum has been shown to depend on the pituitary, and to increase after hypophysectomy. Human GH, while not exhibiting activity itself, if added to the medium simultaneously with serum fraction from hypophysectomized rats, stimulated DNA biosynthesis by fibroblasts significantly. The increase in tritium-thymidine incorporation under the influence of the hormone together with the serum fraction amounted to 233%. It is important to not that serum fraction of intact rats of the same age in a concentration of 1% was unable to induce sensitivity of the fibroblasts to human GH