RELEASE OF PLATELET-DERIVED GROWTH-FACTOR ACTIVITY FROM PIG VENOUS ARTERIAL GRAFTS

Intimal smooth muscle cell proliferation and superimposed atheroma are the main causes of late failure of saphenous vein bypass grafts. It h as been suggested that these reactions are caused by the production of growth factors from the cells of the vessel wall. To test this hypoth esis, we cultured segments of pig venous arterial grafts, removed 1 an d 4 weeks after implantation, in serum-free medium for 24 hours. Tissu e viability as assessed by adenosine triphosphate concentration was ma intained throughout the 24-hour culture period (239 +/- 21 nmol/gm wet weight [standard error of the mean], n = 26, 0 hours; 240 +/- 24 nmol /gm wet weight, n = 17, 24 hours). Cell proliferation occurred and aut oradiography showed proliferating cells to be located in the neointima l and medial layers. These cells were identified as smooth muscle cell s by means of a monoclonal antibody to cr-actin. Graft-conditioned med ia were tested for mitogenic activity by means of a fibroblast prolife ration assay. Media conditioned for 24 hours produced significant stim ulation of cell growth (284% +/- 30%, n = 17) above that obtained in c ulture medium alone (100%). This mitogenic activity was inhibited by 6 1% +/- 9%, n = 8, with a polyclonal-neutralizing antibody to platelet- derived growth factor. Reverse-transcription polymerase chain reaction analysis and Northern blots demonstrated platelet-derived growth fact or B messenger ribonucleic acid (mRNA) in vein grafts but not in ungra fted vein. Analysis of graft tissue sections by in situ hybridization demonstrated an abundance of platelet-derived growth factor B mRNA pos itive cells in the endothelial and neointimal layers, as well as in th e endothelial cells of the adventitial vessels. These data constitute direct evidence for active growth factor production within the cells o f the vein graft. They also suggest that endogenously produced platele t-derived growth factor may play a role in regulating smooth muscle ce ll proliferation in this model.