Interactions between Transforming growth factor- [TGF- ] and nitric oxide [NO] are important in the pathophysiology of unilateral ureteral obstruction [UUO]. Dopamine [DA] is a vasoactive renal mediator active at the D_1A receptor [D_1AR], which has not been studied in UUO; therefore we examined the interactions of DA, TGF- and NO in UUO. In vivo, UUO was carried out in rats with or without concurrent treatment with 1D11, a monoclonal antibody to TGF- , for 14 days. In vitro, NRK-52E cells [normal rat kidney tubules], were treated with DA, and NO and TGF- release were examined. UUO resulted in a 70% decrease in the expression of renal D1AR, confirmed by both western blot analysis and immunohistochemistry. 1D11 treatment restored expression to 60% of control values. DA treatment decreased NRK-52E release of TGF- by 80% ; conversely, DA significantly increased NO release from NRK-52E cells. These results suggest that DA modulates the release of cytokines which are involved in the fibrotic and apoptotic sequelae of UUO and that these effects are independent of DA's known vasoactive properties.