Ability of endothelial cells to condition culture medium

Endothelial cell-conditioned medium contains two classes of factors distinguishable by behavior during dialysis and on specificity for cell type. One species, which diffuses through dialysis tubing with an exclusion limit of 6,000 to 8,000 daltons, supports growth of bovine aortic endothelial (BAE) cells in medium containing a growth limiting concentration of serum (0.2% serum). The production of this material appears to depend upon the presence of serum in the medium being conditioned. The activity increases with time of exposure of BAE cells to serum and with increasing concentration of serum present in the incubation medium. This activity cannot be replaced by exogenous epidermal growth factor, fibroblast growth factor, platelet-derived growth factor, insulin, or thymidine. The second species, the endothelial cell-derived growth factor (ECDGF), is retained by dialysis tubing with an exclusion limit of 6,000 to 8,000 daltons. ECDGF stimulates the growth of smooth muscle cells but does not support BAE cell growth in limiting serum concentrations. unlike the dialyzable species, the production of ECDGF is independent of previous incubation of BAE cell cultures in serum. These studies suggest that BAE cells are able to utilize serum components to produce conditioning factors for their own growth that are distinct from the higher molecular weight ECDGF.