The proliferative response to platelet-derived growth factor of smooth muscle cells isolated from synthetic vascular grafts in a canine model

Objective: Previous studies on graft healing have shown increased platelet-derived growth factor (PDGF) production in graft segments versus native aortic segments. The purpose of this study was to characterize the proliferative response of graft smooth muscle cells (SMCs) to PDGF. Methods: Thoracoabdominal grafts were implanted in beagles. SMCs were harvested from the graft and the proximal and distal aortas. Basal proliferation was assessed with growth curves in primary culture. The proliferative response to PDGF then was compared with [³H]thymidine uptake studies and cell counts. Finally, PDGF receptors were characterized with radio-labeled ligand binding assays. Results: The growth curves showed that the graft SMCs entered log- phase growth 2 days earlier than did the aortic SMCs. Stimulation of quiescent early-passage graft SMCs with PDGF (10 ng/mL) resulted in a 1.7 ± 0.1-fold increase in [³H]thymidine incorporation, which was significantly less than that of the SMCs from both the proximal aorta (11.8 ± 3.0) and the distal aorta (10.2 ± 1.9; P< .5). Similarly, the 1.1 ± 0.1-fold increase in graft SMC cell number was significantly less than the increases for both proximal (2.8 ± 0.5) and distal (2.9 ± 0.8) aortic SMCs (P < .5). Binding studies on quiescent first-passage cells showed fewer PDGF receptors available for binding in the graft SMCs (185 ± 70 fmol/million cells) as compared with both the proximal (419 ± 147 fmol/million cells) and the distal (387 ± 112 fmol/million cells) aortas (P < .5). Binding affinity was similar for the three groups. Conclusion: Graft SMCs exist in a chronic proliferative state but exhibit a decreased proliferative response to PDGF and have fewer receptors available for binding PDGF than do aortic SMCs in vitro.