To investigate the presence and the distribution of preproendothelin-1 (prepro-ET-1) mRNA in human kidney, eight human kidneys obtained at surgery from patients affected by localized renal tumors were studied. Northern blot analysis using a human prepro-ET-1 cDNA probe labeled with 32P showed the presence of a single band of approximately 2.3 kb that was present both in the renal cortex and medulla of all the kidneys studied. Densitometric analysis of hybridization signals demonstrated that prepro-ET-1 mRNA levels in the renal medulla were 2.2-fold higher than those in the renal cortex. The distribution of prepro-ET-1 mRNA in human kidney was investigated by in situ hybridization using a human prepro-ET-1 RNA probe labeled with 35S. The greatest density of prepro-ET-1 mRNA was observed in the renal medulla, where hybridization signal was demonstrated in vasa recta bundles and capillaries and in collecting ducts. By combining in situ hybridization with immunohistochemical detection of von Willebrand factor, we demonstrated that 93 +/- 2.5% of nontubular medullary cells containing prepro-ET-1 mRNA were endothelial cells. In the cortex, prepro-ET-1 mRNA was localized in the endothelial layer of arcuate and interlobular arteries and veins and in the endothelial cells of afferent arterioles. The results of the present study demonstrate that ET-1 gene expression is present in vascular and tubular structures of the human kidney. It is possible that ET-1 synthesized locally in the human kidney represents a local system affecting renal hemodynamics and functions through paracrine and/or autocrine actions on different renal structures.