The assessment of ACE activity in man following angiotensin I challenges: a comparison of cilazapril, captopril and enalapril

Abstract

1. The aim of the studies was to develop a new methodology to estimate the pharmacodynamic properties and potency of angiotensin converting enzyme (ACE) inhibitors in man. 2. Angiotensin I dose-response curves were derived by continuous infusion of angiotensin I in increasing dose steps; steady state was reached within 3 min. 3. Interaction between angiotensin I (agonist) and ACE inhibitors (antagonist) was characterized according to Schild-plot methodology by measuring agonist dose-response curves using diastolic blood pressure in the absence and the presence of varying doses of the antagonist. 4. Cilazapril shifted the angiotensin I dose-response curves to the right. A twofold shift (apparent Ki-dose) was observed with approximately 0.6 mg cilazapril. 5. The effect of angiotensin I on diastolic blood pressure was determined before and up to 36 h after administration of 25 mg captopril, 10 mg enalapril, 4 mg cilazapril and a placebo orally. The pharmacodynamic half-life of captopril was about 2 h, whereas the effect of enalapril and cilazapril was about 4 h. 6. Angiotensin I dose-response curves are useful methods of investigating the pharmacodynamic properties of ACE-inhibitors in man.