Cicletanine ((+/-)3-(4-chlorophenyl)-1,3-dihydro-7-hydroxy-6-methylfuro-[3,4-c] pyridine) 3-(4-chlorophenyl)-1,3-dihydro-7-hydroxy-6-methylfuro-[3,4-c] pyridine) is a novel antihypertensive vasodilator with an incompletely understood mechanism of action. In the studies described here, the release of nitric oxide and superoxide (O2-) stimulated by cicletanine was measured simultaneously in the endothelium of isolated rat aortic rings. Highly sensitive electrochemical nitric oxide and O2- microsensors were placed near the surface of endothelial cells and the kinetics of nitric oxide and O2- release were monitored in situ. The response times for nitric oxide and O2- microsensors were 100 micros and 50 micros, respectively, and detection limit was 10(-9) M. Cicletanine stimulated nitric oxide release in aorta endothelium at (micromolar) therapeutic concentrations that were consistent with the concentrations of the compound to induce endothelium-dependent vasorelaxation in isolated rat aorta. The peak concentration of nitric oxide was 160+/-8 nM. This concentration was about 70% and was 60% lower as compared with the nitric oxide peak concentration observed after stimulation with receptor-independent agonist (calcium ionophore A23187) and receptor-dependent agonist (acetylcholine), respectively. However, after administration of cicletanine, only a small concentration of O2- was recorded (peak 3.1+/-0.2 nM) contrary to a large concentration (27+/-1.35 nM) observed after stimulation with A23187). Cicletanine not only stimulated nitric oxide release but also was a potent scavenger of O2- at nanomolar level. Both of these effects may contribute to potent vasorelaxation properties of cicletanine and its long-term therapeutic actions, resulting in cardiovascular tissue protection.