Growth factors and the vessel wall.

We have tried to review the large and complex literature on vessel wall growth from the viewpoint of humoral factors. The picture is both simple and complex. Two growth factors, PDGF and EGF, can now be chemically defined, and we have begun to understand the way they interact with cells. For one of these growth factors, PDGF, there is good evidence that it has access to the vessel wall and can promote cell replication. The story of other factors is more complex. We still know very little about growth inhibitors, and there is no conclusive evidence that they exist as functional entities in vivo. The work on heparan sulphate could represent the first clear example of negative control of growth. Of the large variety of other factors, it is likely that macrophage-derived growth factor is produced in the vessel wall, and it is possible that the endothelial cell-derived growth factor is made in vivo as well as in vitro. Perhaps our greatest challenge in the near future will be to learn the relative role of each of these factors, as well as their interactions with one another during the progression of atherosclerotic lesions.