Related Experiment Video
Updated: Aug 18, 2026

Receptor Autoradiography Protocol for the Localized Visualization of Angiotensin II Receptors
Published on: June 7, 2016
Pulmonary capillary endothelium-bound angiotensin-converting enzyme activity in humans
S E Orfanos1, D Langleben, J Khoury
1Division of Cardiology, Jewish General Hospital, McGill University, Montreal, P.Q., Canada.
Background:
Pulmonary endothelium has metabolic functions including the conversion of angiotensin I to angiotensin II by angiotensin-converting ectoenzyme (ACE). In this study, we have validated an indicator-dilution technique that provides estimations of dynamically perfused capillary surface area (DPCSA) in humans, and we have characterized pulmonary endothelial ACE in vivo.
Methods And Results:
In 12 adults, single-pass transpulmonary (one or both lungs) hydrolysis of the specific ACE substrate 3H-benzoyl-Phe-Ala-Pro (3H-BPAP) was measured and expressed as % metabolism (%M) and v=-ln(1-M). We also calculated Amax/Km, an index of DPCSA. %M (70.1+/-3.2 vs 67.9+/-3.1) and v (1.29+/-0.14 vs 1. 20+/-0.12) were similar in both lungs and the right lung, respectively, whereas Amax/Km//body surface area decreased from 2460+/-193 to 1318+/-115 mL/min per square meter.
Conclusions:
Pulmonary endothelial ACE activity can be assessed in humans at the bedside by means of indicator-dilution techniques. Our data suggest homogeneous pulmonary capillary ACE concentrations and capillary transit times (tc) in both human lungs, and similar tc within the normal range of cardiac index. Amax/Km in the right lung is 54% of total Amax/Km in both lungs, suggesting that Amax/Km is a reliable and quantifiable index of DPCSA in humans.
Related Concept Videos
Regulation of Angiogenesis and Blood Supply
Transducer Mechanism: Enzyme-Linked Receptors
Major types that are helpful drug targets include:
Heart Failure Drugs: Inhibitors of Renin-Angiotensin System
Treatment for Pulmonary Arterial Hypertension: Endothelin Receptor Antagonists
ETs are synthesized through a complex sequence of enzymatic steps, primarily involving an enzyme referred to as endothelin-converting enzyme (ECE). Of...
Treatment for Pulmonary Arterial Hypertension: Prostacyclin Receptor Agonists
These agonists bind to the IPR receptor situated on the plasma membrane of the pulmonary artery smooth muscle cells. This binding triggers a cascade of reactions known as the GS-AC-cAMP-PKA pathway. This pathway results in the relaxation of smooth muscle...
Heart Failure II: Pathophysiology

