Effects of smooth muscle cell derived growth factor (SDGF) in combination with other growth factors on smooth muscle cells.

Recently intimal thickening was shown to be due to stimulation of proliferation of arterial smooth muscle cells (SMC) by autocrine secretion of growth factor(s). We have reported that cultured rabbit aortic SMC secrete a growth factor (SDGF) distinct from other known growth factors. This paper reports on studies on the biological characteristics of SDGF. Putative "competence" and "progression" growth factors synergistically stimulated DNA synthesis of cultured rabbit aortic SMC. Conditioned medium (CM) from SMC containing SDGF stimulated DNA synthesis in SMC synergistically with either the competence factors or the progression factors. This synergistic effect was also observed in the presence of optimal concentrations of both competence and progression factors. The continuous presence of CM was essential for its stimulation of DNA synthesis whereas the presence of PDGF for only the first 4 h of culture was sufficient to induce maximum stimulation of DNA synthesis. These results suggest that SDGF is a new growth factor distinct from either competence or progression factors and that it stimulates a different pathway in SMC from those stimulated by other known growth factors.