Although pathologic and hemodynamic changes in monocrotaline (MCT)-induced pulmonary hypertension have been studied extensively, relatively little is known about the inter- and intracellular signaling mechanisms underlying such alterations. As a first step to delineating signaling mechanisms governing adverse structural alterations in the hypertensive lungs, we examined changes in the steady-state levels of mRNAs encoding several growth factors including transforming growth factors (TGF), platelet-derived growth factors (PDGF), vascular endothelial cell growth factor (VEGF) and endothelin (ET) as a function of time in MCT-induced pulmonary hypertension in rats. These studies demonstrated a very diverse pattern of growth factor gene expression in response to MCT administration. In general, alterations in the steady-state levels of mRNAs encoding the growth factors preceded the onset of MCT-induced pulmonary hypertension. TGF-β1, -β2 and -β3 transcripts were seen to be elevated, whereas that of TGF-α and PDGF-A remained unchanged. Transcripts for PDGF-B and ET were increased in the early stages but declined to less than controls in the latter stages of MCT-induced hypertension. In contrast, levels of VEGF mRNA decreased to less than controls as the disease progressed. Viewed collectively, the diverse pattern of expression suggests that alterations in the levels of the growth factor transcripts may have a significant role in the development of pulmonary hypertensive disease and may be relevant to the pathological and structural changes in MCT-induced pulmonary hypertension.