Growth hormone-dependent serum stimulation of DNA synthesis in chick embryo fibroblasts in culture.

We have investigated the role of GH in the serum requirement for the multiplication of chick embryo fibroblasts (CEF-S) in culture . Serum from hypophysectomized (hypox.) rats is much less effective than normal serum in stimulating the incorporation of (3H-methyl]thymidine into DNA. More importantly, bovine GH(bGH) treatment of the hypox. rat restores 60% or more of the activity in the 3H-thymidine incorporation assay. Bovine GH is inactive when tested directly in the assay. Mixing experiments show that the decreased activity of hypox. serum is not due to the presence of an inhibitor in the hypox. serum. The GH is dependent factor is nondialysable and stable to Boiling at pH5.5. boiling the normal, hypox. and bGH treating hypox. rat sera results not only in enhancement of the activity but also a more linear dose response curve in the 3H-thymidine incorporation assay. The thesis because measurements of cell numbers show the CEFs multiply less well in boiled normal rat serum and bGH treatment of the hypox. rat restores approximately half of the multiplication stimulating activity of normal boiled rat serum. CEFs in culture may provide a satisfactory in vitro system for the study of the mechanism of action of the growth hormone dependent anabolic factors found in serum.