Effects of platelet-contained growth factors (PDGF, EGF, IGF-I, and TGF-beta) on DNA synthesis in porcine aortic smooth muscle cells in culture.

Platelet-derived growth factor (PDGF), epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I), and transforming growth factor-beta (TGF-beta) are potent mitogens present in human platelets. Since they are likely to be released simultaneously at the site of vessel injury, their combined effects on vascular smooth muscle cells are more relevant physiologically than their individual actions. Therefore, we added various concentrations of growth factors to quiescent porcine aortic smooth muscle cells cultured in low-serum (0.5%) medium and measured the amount of [3H]thymidine incorporated into DNA. Effect of TGF-beta alone was concentration-dependent: stimulatory (1.5-fold increase over the basal) at 0.025 ng/ml and inhibitory at greater than or equal to 0.1 ng/ml. Effects of the other three growth factors on DNA synthesis were only stimulatory; their maximally effective concentrations were 20 ng/ml for PDGF (eightfold over the basal), 40 ng/ml for EGF (six-fold increase), and 20 ng/ml for IGF-I (fourfold increase). When PDGF, EGF, and IGF-I were added at submaximally effective concentrations, their effects were additive. TGF-beta at 1 ng/ml inhibited at least 50% of the effects of 20 ng/ml EGF and of 10 ng/ml IGF-I, whereas inhibition of the effect of 10 ng/ml PDGF required 10 ng/ml of TGF-beta. The concentration of TGF-beta needed to inhibit 50% of the combined effect of EGF, IGF-1, and PDGF was 5 ng/ml. These results show complex interrelationships between the growth factors contained in the alpha-granules of human platelets in their effects on porcine aortic smooth muscle cells.