The inhibitor of cytochrome P-450 cimetidine was used to assess the role of cytochrome P-450-dependent enzymes for cyclic GMP stimulation by glyceryl trinitrate in a kidney epithelial cell line (LLC-PK1). Pretreatment of the cells with 0.1 mmol/l cimetidine markedly decreased cyclic GMP stimulation by glyceryl trinitrate (0.03-1 mumol/l). In the presence of 0.1 mmol/l cimetidine, the 14-fold cyclic GMP stimulation observed at 1 mumol/l glyceryl trinitrate was reduced by 66%. Glyceryl trinitrate-induced cyclic GMP stimulation remained unaltered by ranitidine (0.1 mmol/l), which has a much lower affinity for the cytochrome P-450 enzyme system. Another inhibitor of cytochrome P-450, miconazole (0.1 mmol/l), also attenuated glyceryl trinitrate-induced cyclic GMP stimulation. In contrast, cimetidine and miconazole did not affect cyclic GMP stimulation by sodium nitroprusside that spontaneously releases nitric oxide. These results suggest that in intact cells, glyceryl trinitrate-induced cyclic GMP stimulation is dependent on cytochrome P-450 enzymes which may be relevant for nitric oxide formation from organic nitrates.