Kinins IV pp 453-459 | Cite as

In Vivo Determinations of Ki Values for Angiotensin Converting Enzyme Inhibitors

  • John D. Catravas
  • Betty L. Anthony
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 198A)


We present two methods for calculating Ki values of angiotensin converting enzyme (ACE) inhibitors, such as captopril, in anesthetized or conscious rabbits. Both methods are based on indicator-dilution type determinations of single pass transpulmonary metabolism of the ACE substrate benzoyl-phe-ala-pro (BPAP). The first method involves two determinations of Michaelis-Menten constants Km and Amax (product of Vmax and lung capillary plasma volume) of endothelial-bound ACE for BPAP. Thirty seconds before the second determination of kinetic constants, the inhibitor is administered iv (e. g. captopril, 12 nmol/kg). Comparisons of the apparent Km and Amax values, obtained after the inhibitor to the control values obtained from the first determination, provide Ki values. With the second method, the ratio Amax/Km is obtained, under first-order reaction conditions, before and 30 sec after administration of inhibitor. These apparent and control ratios are used to calculate Ki values. In both methods, plasma levels of the inhibitor at the time of the determination of apparent kinetic constants are estimated by injecting radio-labelled inhibitor (e. g. 3H-captopril), analyzing radioactivity in arterial samples and correcting for plasma protein binding. These methods are potentially applicable to the clinical evaluation of new ACE inhibitors, in vivo, under normal or pathologic conditions.


Angiotensin Converting Enzyme Angiotensin Converting Enzyme Inhibitor Pulmonary Blood Flow Evans Blue Anesthetize Rabbit 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. 1.
    J. D. Catravas and R. E. White, Kinetics of angiotensin converting enzyme and 5’-nucleotidase, in vivo, J. Appl. Physiol. 57: 1173–1181 (1984).PubMedGoogle Scholar
  2. 2.
    J. D. Catravas, Michaelis-Menten kinetics of pulmonary angiotensin converting enzyme in the conscious rabbit, in: “Kinin IV” (1986).Google Scholar
  3. 3.
    I. H. Segel, “Enzyme Kinetics,” Wiley, New York (1975).Google Scholar
  4. 4.
    J. W. Ryan, Assay of peptidase and protease enzymes, in vivo, Biochem. Pharmacol. 32: 2127–2137 (1983).PubMedCrossRefGoogle Scholar
  5. 5.
    D. W. Cushman, H. S. Cheng, E. F. Sabo, and M. A. Ondetti, Design of new antihypertensive drugs: Potent and specific inhibitors of angiotensin converting enzyme, Prog. Cardiovasc. Pis. 21: 176–182 (1978).CrossRefGoogle Scholar
  6. 6.
    D. W. Cushman, H. W. Cheng, E. F. Sabo, and M. A. Ondetti, Design of potent competitive inhibitors of angiotensin converting enzyme. Carboxyalkanoyl and marcapto alkanoyl amino acids, Biochem. 16: 5484–5491 (1977).CrossRefGoogle Scholar
  7. 7.
    F. A. O. Mendelsohn, J. Csicsmann, and J. S. Hutchinson, Complex competitive and non-competitive inhibition of rat lung angio- tensin-converting enzyme by inhibitors containing thiol groups: Captopril and SA 446, Clin. Sci. 61: 277s–280s (1981).Google Scholar
  8. 8.
    X. Chen, B. R. Pitt, R. Moalli, and C. N. Gillis, Correlation between lung and plasma angiotensin converting enzyme and the hypotensive effect of captopril in conscious rabbits, J. Pharmacol. Exp. Ther. 229: 649–653 (1984).PubMedGoogle Scholar

Copyright information

© Plenum Press, New York 1986

Authors and Affiliations

  • John D. Catravas
    • 1
  • Betty L. Anthony
    • 1
  1. 1.Department of Pharmacology and ToxicologyMedical College of GeorgiaAugustaUSA

Personalised recommendations