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Assay of Pulmonary Microvascular Endothelial Angiotensin Converting Enzyme, in Vivo: Comparison of Three Methods

  • S. E. Orfanos
  • X-L Chen
  • J. W. Ryan
  • A. Y. K. Chung
  • S. E. Burch
  • J. D. Catravas
Part of the NATO ASI Series book series (NSSA, volume 257)

Abstract

We monitored the activity of pulmonary microvascular endothelial-bound angiotensin converting enzyme (ACE), in vivo, by means of multiple indicator-dilution type techniques, utilizing three different probes: the hydrolysis of two substrates, 3H-benzoyl-Phe-Ala-Pro (BPAP) and 14C-benzoyl-Ala-Gly-Pro (BAGP), and the binding of the inhibitor 3H-RAC-X-65 (RAC), all measured during a single transpulmonary passage in anesthetized rabbits, placed on total heart by-pass, so that both systemic and pulmonary circulations were fully supported by means of a two-channel extracorporeal pump. Experiments were performed at pulmonary blood flows ( \(\mathop Q\limits\) b) of 250, 400, 560 and 800 ml/min, in control or indomethacin pretreated rabbits. We also investigated the activity of pulmonary microvascular endothelial-bound 5′-nucleotidase (NCT), by measuring the dephosphorylation of its natural substrate 14C-5′-AMP. We calculated substrate utilization, mean lung transit time ( \(\mathop t\limits\) ), and volume of distribution (i.e., central blood volume) of all three substrates, as well as inhibitor binding. We also calculated Amax/Km and Bmax, the modified parameters for substrates and inhibitor, respectively. As \(\mathop Q\limits\) b increased, Amax/Km values for all three substrates and Bmax increased linearly, indicating microvascular recruitment. In experiments where either BPAP and 5′-AMP metabolism, or BAGP metabolism and RAC binding were studied concomitantly, a linear relationship was observed between \(\mathop Q\limits\) b-induced changes in Amax/Km values of BPAP vs 5′-AMP as well as in Amax/Km of BAGP vs B. of RAC. Similarly, increasing \(\mathop Q\limits\) b increased central blood volume and decreased \(\mathop t\limits\), substrate utilization and inhibitor binding.

Keywords

Angiotensin Converting Enzyme Natural Substrate Substrate Utilization Pulmonary Circulation Pulmonary Blood Flow 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Copyright information

© Springer Science+Business Media New York 1993

Authors and Affiliations

  • S. E. Orfanos
    • 1
  • X-L Chen
    • 1
  • J. W. Ryan
    • 2
  • A. Y. K. Chung
    • 2
  • S. E. Burch
    • 3
  • J. D. Catravas
    • 1
  1. 1.Department of Pharmacology & ToxicologyMedical College of GeorgiaAugustaUSA
  2. 2.Department of MedicineUniversity of Miami School of MedicineMiamiUSA
  3. 3.Department of RadiologyMedical College of GeorgiaAugustaUSA

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