AbstractEndothelial cells, including human umbilical vein endothelial cells (HUVEC), bovine aortic endothelial cells (BAEC), and bovine capillary endothelial cells (BCEC) in culture synthesize basic fibroblast growth factor (bFGF) and transforming growth factor type beta (TGF-beta). Basic FGF was cell-associated and synthesis was demonstrated by (i) the presence of bFGF mRNA species, (ii) binding to heparin-Sepharose and elution at 1.5 M NaCI, (iii) cross-reactivity with anti-bFGF antibodies when analyzed by electrophoretic blotting, and (iv) biological activity. Basic FGF was found in cell lysates at 2.3 ng/306cells in HUVEC, 2.0 ng/106cells in BCEC, and 13 ng/106cells in BAEC. TGF-beta was secreted into media, and synthesis was demonstrated by (i) presence of TGF-beta mRNA species, (ii) cross-reactivity with anti-TGF-beta antibodies when analyzed by immunoprecipitation, (iii) competitive binding with authentic human platelet-derived TGF-beta that was blocked by TGF-beta specific blocking antibodies, and (iv) inhibition of [3H]TdR incorporation in CCI-64 cells. TGF-beta was secreted in an inactive form and required acid activation for detection. HUVEC synthesized 2.0 ng TGF-beta/106cells per 12 hr; BCEC, 3.5 ng; and BAEC, 3.5 ng. HUVEC proliferation was not affected by treatment with exogenous TGF-beta, while BCEC proliferation was decreased by treatment with TGF-beta. Vascular endothelium is thus a source for these two potent multifunctional regulatory molecules, both of which may affect the growth of endothelium and neighboring fibroblasts, smooth muscle cells and white blood cells. The activation or release of these factors by endothelium may be a precipitating event in important cellular processes such as wound healing, organogenesis, and angiogenesis.