The vasodepressor mechanism of 2-(1-octynyl)-adenosine (YT-146), a selective adenosine A2 receptor agonist, was compared with that of adenosine in spinally anaesthetized dogs whose blood pressure was kept elevated with i.v. infusion of noradrenaline. Cumulative i.v. administration of YT-146 (1-1000 nmol/kg) caused a slowly developing and long-lasting decrease in mean blood pressure (MBP) and a small decrease in heart rate (HR) at high doses, whereas single i.v. administration of adenosine caused short-lived decreases in MBP and HR. In dogs given glibenclamide (6 mumol/kg i.v.) or theophylline (30 mumol/kg i.v.) dose-response curves for decrease in MBP due to YT-146 underwent parallel rightward shifts. The ED50 values for YT-146 were increased about 5.5-fold with glibenclamide and about 11.9-fold with theophylline. However, no further rightward shifts of the curves were obtainable in dogs given glibenclamide plus theophylline; the increase in ED50 values for YT-146 was about 6.8-fold, being close to the increase obtained with theophylline alone. The ED50 values for adenosine to lower MBP increased about 1.6-fold with theophylline but not with glibenclamide. Glibenclamide and theophylline failed to antagonize the negative chronotropic effects of both drugs. These results suggest that the vasodepressor effect of YT-146 involves two mechanisms following stimulation of adenosine A2 receptors; one is probably a cyclic AMP-dependent mechanism and the other is the opening of glibenclamide-sensitive K+ channels.