Intimal injury in vivo activates vascular smooth muscle cell migration and explant outgrowth in vitro.

In vivo induced endothelial injury results in an intimal thickening, mainly caused by stimulation of smooth muscle cells (SMC), which migrate into, and proliferate in, the denuded intima. We evaluated the manifestation and persistence of this stimulus in several in vitro explant and growth assays using aortic explants from either balloon catheter-injured rats or from sham-operated controls. SMC outgrowth from control explants started 48 hours after explantation, became half-maximal after 96 hours, with 74% of the explants showing outgrowth. Explants from balloon-injured aortas showed SMC outgrowth within 24 hours, became half-maximal after 48 hours, with 92% of the explants showing outgrowth. An interval of 4 to 7 days between balloon injury and sacrifice was optimal for obtaining accelerated outgrowth, while a 1-day interval showed a weak stimulation and a 21-day interval had no such effect. The in vivo stimulated cells grew more rapidly, resulting in a greater colony size per explant, and they became temporarily serum-independent. Increased growth rate persisted up to the second subculture but returned to normal in subsequent passages. Mechanisms of SMC migration can now be quantitatively assessed by replacing the intima with the tissue culture dish, allowing studies on the extent and persistence of atherogenic stimuli.