Scleral fibroblasts of the chick embryo proliferate by an autocrine mechanism in protein-free primary cultures: Differential secretion of growth factors depending on the growth state

Abstract Scleral fibroblasts of the chick embryo in primary culture proliferated in a protein-free medium. Conditioned medium (CdM) from the culture contained plural growth-promoting factors, which were active to the same cell type. The activity of one of the growth-promoting factors (SAF-I) was heat-resistant and the rest (SAF-II) were heat-sensitive. SAF-I accumulated in the CdM only during the growing phase; on the other hand, SAF-II accumulated in the CdM during the stationary phase. SAF-I showed the same time course of DNA synthesis-promoting activity as human PDGF. However, the activity of the SAF-I was not neutralized by anti-human PDGF. On the other hand, a part of the SAF-II (SAF-IIa) showed a strong affinity for heparin.