ABSTRACT
Trandolapril (RU 44570), a new non-sulfhydryl angiotensin-converting enzyme (ACE) inhibitor chemically related to enalapril, and its diacid (RU 44403), were investigated for their ability to inhibit angiotensin-converting enzyme. Trandolapril attenuated angiotensin I (Ang I)-induced pressor responses following i.v. administration to rats and dogs with ID50 values of 13.1 +/- 1.3 and 21.1 +/- 2.3 micrograms/kg. RU 44403 produced corresponding values of 9.9 +/- 0.7 and 7.2 +/- 2.3 micrograms/kg. Trandolapril (3-300 micrograms/kg) produced a dose-related attenuation of Ang I-induced pressor responses (ID50 30 micrograms/kg) following oral administration to rats. Oral administration of trandolapril (30-1000 micrograms/kg) to dogs inhibited Ang I pressor responses for over 6 h. The depressor action of bradykinin in the rat was potentiated by i.v. trandolapril and RU 44403 with ED50 values of 5.5 +/- 0.8 and 4.9 +/- 0.3 micrograms/kg respectively. Trandolapril was 2.3-10-fold more potent than enalapril in all experiments, depending on species or route of administration. RU 44403 and MK 422 were approximately equipotent, implying that trandolapril was more readily hydrolysed than enalapril. Trandolapril (0.3-30 mg/kg) produced dose-related, long-lasting (greater than 24 h) reductions in blood pressure (BP) in spontaneously hypertensive rats (SHR) following oral administration. The anti-hypertensive effect was potentiated significantly in hydrochlorothiazide-pretreated SHR when the plasma renin activity was increased. Enalapril was 10-fold less potent than trandolapril in reducing BP. The anti-hypertensive action of trandolapril (3 mg/kg) was abolished in SHR that were bilaterally nephrectomized 24 h beforehand, but was maintained in SHR pretreated by indomethacin (5 mg/kg p.o.). Trandolapril (1 mg/kg i.v.) produced a modest and transient reduction in BP in anesthetized dogs. Trandolapril produced dose-related (30-1000 micrograms/kg) reductions in BP, total peripheral resistance and heart work in dogs pretreated with hydrochlorothiazide to increase plasma renin activity.
