PLATELET-DERIVED GROWTH-FACTOR (PDGF) ACCELERATES INDUCTION OF COMPETENCE, AND HEPARIN DOES NOT INHIBIT PDGF-INDUCED COMPETENCE IN PRIMARY CULTURED SMOOTH-MUSCLE CELLS OF RAT AORTA

The time-dependent effect of platelet-derived growth factor (PDGF) on cell proliferation was investigated to clarify whether PDGF accelerates the rate of proliferation or its start in primary cultured smooth muscle cells (SMC) of rat aorta. In synchronized SMC at the G0 phase, 1, 10 and 100 ng/ml PDGF started DNA synthesis at 24, 15 - 18 and 12 hr, respectively, after stimulation by 3% fetal bovine serum (FBS) or hypophysectomized rat plasma (deficient in insulin-like growth factor-I (IGF-I)). Heparin (1, 10 or 100-mu-g/ml) decreased only the rate of DNA synthesis stimulated by PDGF in synchronized SMC. DNA synthesis in non-synchronized cells stimulated by PDGF with FBS was determined up to 10 days in culture. The stimulation with 1 % FBS plus 30 ng/ml PDGF potentiated the DNA synthesis which was saturated with stimulation by 10% FBS alone, suggesting that prolonged treatment of PDGF transforms SMC. These results demonstrated that PDGF concentration-dependently accelerated the induction of competence independently of IGF-I, and heparin did not inhibit PDGF-induced competence but inhibited progression in primary cultured SMC of rat aorta.