THROMBIN-INDUCED MITOGENESIS OF VASCULAR SMC IS PARTIALLY MEDIATED BYAUTOCRINE PRODUCTION OF PDGF-AA

Previous studies have shown that alpha-thrombin (Thr) is a mitogen for cultured smooth muscle cells (SMC), but controversy exists concerning mechanisms of growth stimulation. The purpose of these studies was to determine whether autocrine production of platelet-derived growth fac tor-AA (PDGF-AA) mediated Thr-induced SMC mitogenesis. SMC derived fro m aortae of Sprague-Dawley rats were grown to confluence, growth arres ted in serum-free medium, and treated. Conditioned medium (CM) was har vested by adding bovine serum albumin as a carrier and hirudin to neut ralize residual Thr. Results demonstrated that CM from Thr-treated SMC (Thr CM) had increased mitogenic activity compared with control CM (C nt CM) and that PDGF-AA levels were increased 12-fold in Thr CM compar ed with Cnt CM. The excess mitogenic activity in Thr CM was markedly i nhibited by PDGF-AA-neutralizing antibodies. Cotreatment with Thr and PDGF-AA-neutralizing antibodies resulted in a 30% decrease in Thr-indu ced [3 H]thymidine incorporation. These results demonstrate that autoc rine production of PDGF-AA partially mediated Thr-induced SMC mitogene sis.