The antihypertensive and cough suppressant mechanisms of DU-1777 ((2S,3aS,7aS)-1-(N2-nicotinoyl-L-lsyl-gamma-D-glutamyl )octahydro-1H-indole-2 -carboxylic acid, CAS 116662-73-8), a new long-acting angiotensin-1-converting enzyme (ACE) inhibitor, were investigated in vivo and in vitro. The antihypertensive effects of DU-1777 at 10 mg/kg p.o. and cromakalim at 0.3 mg/kg p.o. were partially (about 60%) or fully antagonized by glibenclamide at 10 mg/kg i.v. in 2-kidney, 1-clip renal hypertensive rats (2K-1C RHR). The antihypertensive effects of a Ca blocker (nifedipine) and other ACE inhibitors (captopril, alacepril, enalapril, lisinopril, imidapril and quanapril) were not antagonized by glibenclamide. In deoxycorticosterone acetate-salt hypertensive rats (DOCA-HR), the antihypertensive effects of DU-1777 at 3-30 mg/kg p.o. were fully antagonized by glibenclamide. However, in vitro, DU-1777 (10(-6)-10(-3) mol/l) did not affect aortic ring contractions induced by high K (30 mmol/l). In guinea pig, citric acid induced cough was increased by ACE inhibitors, captopril, alacepril, enalapril and lisinopril (10 and 30 mg/kg p.o.). DU-1777 had a tendency to decrease citric acid induced cough and the effect was antagonized by glibenclamide. These results suggest that while DU-1777 itself does not open ATP-dependent K channel, it indirectly produces these effects through unknown mechanisms in vivo. Moreover, these effects contributed to the antihypertensive effect in DOCA-HR and cough suppressant effect in guinea pigs.