Shear stress influences the release of platelet derived growth factor and basic fibroblast growth factor by arterial smooth muscle cells

Objectives: To determine the correlation between haemodynamic forces and the release of two mitogens for smooth muscle cells (SMC): Platelet Derived Growth Factor (PDGF) and basic Fibroblast Growth Factor (bFGF). Methodology: Bovine aortic smooth muscle cells were seeded on fibronectin coated polystyrene cylinders and allowed to reach confluence. The cells were subjected to a laminar flow of 50 cc/min (3 dyne/cm2), 100 cc/min (6 dyne/cm2) and 150 cc/min (9 dyne/cm2) in an in vitro system. Control cells were subjected to similar incubation conditions without flow. Principal results: Shear stress increased the release of mitogens by SMC. The release of mitogens was proportional to the level of shear stress and was still evident 24 hours after flow cessation. Conditioned serum-free medium from SMC subjected to shear stress increased tritiated thymidine uptake in Swiss 3T3 fibroblasts 13-fold as compared to conditioned serum-free medium from control SMC and not subjected to shear stress (p < 0.01) and threefold as compared to standard control (p < 0.001). Addition of an excess of anti-PDGF antibody reduced the mitogenic activity of the conditioned medium by 30% (p < 0.01). Addition of an excess of anti-bFGF antibody reduced the mitogenic activity of the conditioned medium by 60% (p < 0.01). Conclusions: Increasing shear stress promotes the release of both PDGF and bFGF from arterial SMC in culture and is a possible explanation for atherosclerosis formation.