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Early pulmonary endothelial enzyme dysfunction after phorbol ester in conscious rabbits
J R McCormick1, R Chrzanowski, J Andreani
1Veterans Administration Medical Center, Augusta, Georgia.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|November 1, 1987
Summary
Phorbol myristate acetate (PMA) causes pulmonary capillary injury in rabbits, leading to decreased angiotensin converting-enzyme (ACE) activity and endothelial cell dysfunction. This functional injury occurs before any observable structural damage to the lungs.
Area of Science:
- Pulmonary physiology
- Enzymology
- Endothelial cell biology
Background:
- Angiotensin converting-enzyme (ACE) plays a crucial role in cardiovascular regulation.
- Phorbol myristate acetate (PMA) is known to induce inflammatory responses and affect endothelial cells.
- Understanding the early functional changes in pulmonary endothelium is vital for diagnosing and treating lung injury.
Purpose of the Study:
- To investigate the effect of PMA on ACE activity in conscious rabbits.
- To determine if PMA-induced changes in ACE activity are due to altered enzyme kinetics or reduced endothelial surface area.
- To assess early functional injury to pulmonary capillaries.
Main Methods:
- Conscious rabbits were administered PMA intravenously.
- ACE activity was measured in vivo using transpulmonary metabolism of a synthetic substrate ([3H]BPAP).
- Enzyme kinetics (Km and Amax) were analyzed to differentiate between enzyme dysfunction and changes in surface area.
Main Results:
- PMA administration led to granulocytopenia and thrombocytopenia.
- Transpulmonary metabolism of [3H]BPAP and apparent ACE activity decreased significantly post-PMA.
- Increased Km for ACE and 5'-nucleotidase at 1 hour after PMA, with unaffected Amax, indicated enzyme dysfunction independent of surface area.
- No histological lung injury was observed.
Conclusions:
- Low-dose PMA induces functional injury to pulmonary capillary endothelial cells.
- This injury is characterized by enzyme dysfunction rather than a reduction in capillary surface area.
- Functional endothelial damage precedes structural damage in PMA-induced lung injury.