AbstractThis study reports that exposure of endothelial cells [bovine aortic endothelial cells (BAEC) and porcine aortic endothelial cells (PAEC)] to ionizing radiation leads to activation of the basic fibroblast growth factor (bFGF) and platelet‐derived growth factor (PDGF)‐B genes. Nuclear RNA run‐on experiments showed an increase in nuclear RNA of these factors within 90 min after delivery of a dose of 4 Gy. In addition, there was a dose‐and time‐dependent transient increase in bFGF and PDGF‐B mRNA transcripts, although there were differences in the kinetics of these responses between BAEC and PAEC. Radiation‐induced activation of the bFGF and PDGF‐B genes was also manifested by secretion of the corresponding proteins into the culture media of the irradiated endothelial cells. In contrast, the acidic fibroblast growth factor (aFGF), PDGF‐A, and transforming growth factor beta (TGFβ) genes were not concomitantly activated in these cells, as indicated by lack of increase in their mRNA levels. Activation of specific growth factor genes and the extracellular secretion of their products may play an important role in modulating the radidation response via autocrine or paracrine mechanisms. © 1