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Endotoxin-induced increased alveolar capillary membrane permeability
Abstract:
In an attempt to define the effects of endotoxin on the permeability of the pulmonary alveolar capillary membrane (ACM) to a variety of substances [molecular weight (MW) varying from 60 to 69,000], we studied the movement of specific molecular species from the pulmonary capillary blood to the saline-filled "alveolus," employing an in vivo dog lung model. Following endotoxin injection (2-2.5 mg/kg) baseline T1/2 values (time, in minutes, for 50% equilibration of the specific solute between the blood and the saline-filled lung) decreased as follows (compared to baseline values): urea (MW 60) - 42.5 +/- 24 to 21.3 +/- 18; sucrose (MW 360) - 201 +/- 72 to 76 +/- 53; 3,000 MW dextran - 1,275 +/- 746 to 686 +/- 433; 10,400 MW dextran - 1,871 +/- 845 to 1,052 +/- 630 (all p less than 0.05). Neither 20,000 MW dextran nor albumin (MW 69,000) showed an increased permeability following endotoxin injection. Histamine analysis revealed a significant increase in all lung liquid samples post-endotoxin injection without a significant increase in blood histamine values. We conclude that, acutely (within 4 hr of injection), endotoxin causes an increase in permeability of the ACM for substances up to 10,400 MW. The role of histamine in this increased permeability remains controversial.
Insights
Endotoxin acutely increases the permeability of the pulmonary alveolar capillary membrane (ACM) to molecules up to 10,400 MW. Larger molecules like albumin were unaffected, and histamine
Area of Science:
- Pulmonary Physiology
- Endotoxin Research
- Capillary Permeability
Background:
- Endotoxin's effects on lung physiology are complex.
- Understanding alveolar capillary membrane (ACM) permeability is crucial for respiratory health.
Purpose of the Study:
- To investigate the impact of endotoxin on ACM permeability.
- To determine the molecular weight cutoff for endotoxin-induced permeability changes.
Main Methods:
- Utilized an in vivo dog lung model.
- Measured the movement of various molecular weight solutes across the ACM post-endotoxin injection.
- Analyzed histamine levels in lung liquid and blood.
Main Results:
- Endotoxin significantly increased ACM permeability for solutes up to 10,400 MW.
- No significant permeability increase was observed for 20,000 MW dextran or albumin (69,000 MW).
- Lung liquid histamine increased, but blood histamine did not, suggesting local effects.
Conclusions:
- Endotoxin acutely enhances ACM permeability for small to medium-sized molecules (up to 10,400 MW).
- The precise role of histamine in this endotoxin-induced permeability increase requires further investigation.