The mode of action of KRN2391 [N-cyano-N'-(2-nitroxyethyl)-3- pyridinecarboximidamide monomethanesulfonate] in coronary circulation was examined in anesthetized dogs in comparison with those of nicorandil and nifedipine. Administration of KRN2391 (10 micrograms/kg i.v.), nicorandil (300 micrograms/kg i.v.), and nifedipine (3 micrograms/kg i.v.) caused an increase in coronary blood flow (CBF) and decreases in mean blood pressure (MBP) and in coronary vascular resistance (CVR). Heart rate (HR) was slightly and simultaneously increased by the drugs. Glibenclamide (5 mg/kg i.v.) blocked the changes of these parameters caused by KRN2391 and nicorandil, but not those caused by nifedipine. The present study suggests that the mechanism of action through ATP-sensitive K channels which are blocked by glibenclamide may contribute, at least in part, to the effects of KRN2391 and nicorandil on CBF and blood pressure (BP).