Growth regulation in primary culture of rabbit arterial smooth muscle cells by platelet-derived growth factor, insulin-like growth factor-I, and epidermal growth factor.

Many studies have linked the proliferation of smooth muscle cells (SMC) to the development of atherosclerotic lesions. We examined the effects of platelet-derived growth factor (PDGF), insulin-like growth factor-I (IGF-I), and epidermal growth factor (EGF) on the regulation of SMC grown on type I collagen-coated dishes in serum-free primary culture. When added alone, PDGF (10 ng/ml), IGF-I (20 ng/ml), and EGF (10 ng/ml) produced minimal effects on BrdU (5-bromo-2'-deoxyuridine) incorporation into cellular DNA and on cell growth. However, simultaneous addition of PDGF and IGF-I significantly stimulated DNA synthesis and cell growth. The combination of PDGF, IGF-I, and EGF synergistically stimulated DNA synthesis and cell proliferation. Flow cytometric analysis indicated that type I collagen alone promoted the phenotypic modulation and progression of the cells from the G0 (contractile phenotype) to the G1A phase (intermediate phenotype), PDGF and IGF-I, together, stimulated the rate of cell transition from the G1A to the G1B and S phases (synthetic phenotype), and PDGF, IGF-I, and EGF together stimulated the rate of cell transition into the S and G2+ M phases. In contrast, in quiescent secondary cultured SMC (G1B phase), PDGF alone was able to initiate DNA synthesis, although IGF-I and EGF were required to complete DNA synthesis. These results reveal that PDGF and IGF-I stimulate the cells to complete the G1A phase and proceed to the G1B phase and that EGF regulates the rate of entry into the S phase in rabbit SMC in primary culture. Furthermore, differences in the responsiveness to these growth factors between primary and secondary cultures reflected the varying phenotypic properties of vascular SMC.