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The effect of the three platelet-derived growth factor (PDGF) isoforms AA, AB, and BB on migration was investigated in cultured human saphenous vein smooth muscle cells. The modified Boyden chamber technique yielded efficacies BB >> AB, AA = 0. However, the BB concentration-response relationship displayed a pronounced peak, occurring between 1 and 10 ng/mL, with no response above this range. Checkerboard analysis showed that the promotion of migration at low concentrations was chemotactic in nature but that the downturn was independent of gradient. Furthermore, at high concentrations BB was able to prevent chemotaxis induced by fetal calf serum and epidermal growth factor (EGF). Experiments using low concentrations of BB in combination with high concentrations of AA to saturate PDGF alpha-receptors in the presence and absence of a neutralizing antibody to alpha-receptors revealed that alpha-receptor activation induced partial inhibition of chemotaxis but this did not account for the inhibition of migration by high concentrations of BB. Despite possessing no significant chemotactic action itself, high concentrations of the AB isoform completely inhibited BB induced chemotaxis. Taken together these results suggest that the chemotactic signal induced by PDGF is dominated by PDGF beta-receptors and switches from positive at low concentrations to negative at higher concentrations. Stimulation of DNA synthesis by the three isoforms (as measured by [3H] thymidine incorporation) yielded saturable responses for the AB and BB isoforms, with similar efficacy and weak or no response for the AA isoform. Concentration-dependent patterns of tyrosine phosphorylation of certain proteins mirrored the form of the chemotactic response and suggest one possible underlying regulatory mechanism to account for the disparity between PDGF-induced chemotaxis and DNA synthesis.

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Background-Vascular smooth muscle cell (VMSC) proliferation is an essential component of myointimal hyperplasia, which is implicated in the failure of 30% to 50% of vascular interventions, such as coronary angioplasty and peripheral vein grafting. We have shown that cells derived from stenotic lesions in infrainguinal vein grafts were significantly more resistant than controls to growth inhibition by heparin. Methods and Results-In a prospective study, we correlated antiproliferative responses to heparin in vitro with graft patency after 1 year. Sixty-two patients with infrainguinal vein grafts were entered into a graft surveillance program for Ն1 year. At operation, saphenous vein segments were explanted for VSMC culture. Cell proliferation in response to fetal calf serum was later determined in the presence and absence of heparin. In 35 cell cultures, including 13 from the above-mentioned patients, [ 3 H]heparin binding was also estimated. VSMCs from patients with patent grafts were significantly more sensitive to growth inhibition by heparin than cells from patients with stenoses (median, 54% versus 20.9%, PϽ0.001), and [ 3 H]heparin binding was strongly correlated with inhibition of proliferation (rϭ0.81). Conclusions-Responsiveness to heparin in cultured VSMCs is a strong predictor of outcome for infrainguinal vein grafts, and reduced sensitivity to heparin is correlated with decreased heparin binding. Relative resistance to the antiproliferative action of heparin may be a marker for aberrant regulation of VSMC growth.