Prolonged incubation with 1 nmol/L interleukin-1 induced high levels of nitric oxide release and cytotoxicity in vascular smooth muscle cells. NG-Monomethyl-L-arginine, an inhibitor of nitric oxide synthesis, inhibited interleukin-1-induced cytotoxicity at a concentration of 3 mmol/L. Furthermore, prolonged incubation with 0.1 mmol/L sodium nitroprusside, a nitric oxide donor, also induced cytotoxicity. On the other hand, endothelin-1 at concentrations from 10(-10) to 10(-7) mol/L induced a concentration-dependent enhancement of cytotoxicity induced by interleukin-1. However, endothelin-1 did not affect interleukin-1-induced nitric oxide production. Coculture study of vascular smooth muscle cells and endothelial cells without direct cell contact revealed that incubation for 72 hours with interleukin-1 induced high levels of nitric oxide release from cocultured vascular smooth muscle cells to the same degree as release from vascular smooth muscle cells alone. However, interleukin-1-induced cytotoxicity was more enhanced in cocultured vascular smooth muscle cells than in vascular smooth muscle cells alone. Furthermore, coincubation with 20 nmol/L BQ-485, an antagonist of one type of endothelin receptor (ETA), prevented the enhancement of interleukin-1-induced cytotoxicity in cocultured vascular smooth muscle cells. These findings suggest that endothelin-1 secreted from endothelial cells may enhance nitric oxide-induced cytotoxicity by means of the ETA receptor in vascular smooth muscle cells.