Increased sheep lung vascular permeability caused by histamine.

Area of Science:

• Pulmonary Physiology
• Vascular Biology
• Pharmacology

Background:

• Histamine is a known mediator of vascular permeability in systemic circulation.
• Its role in increasing lung vascular permeability to proteins requires further elucidation.

Purpose of the Study:

• To investigate the effect of histamine on lung vascular permeability to proteins in unanesthetized sheep.
• To compare histamine's effects with those of mechanically elevated lung vascular pressures.

Main Methods:

• Utilized steady-state infusions of histamine in unanesthetized sheep with surgically implanted catheters.
• Measured pulmonary artery pressure, left atrial pressure, lung lymph flow, and lymph protein content.
• Assessed permeability-surface area (PS) products for various protein fractions.

Main Results:

• Histamine caused a dose-related, reversible increase in lung lymph flow and lymph protein clearance.
• Unlike mechanically elevated pressures, histamine did not decrease lymph-plasma protein ratios despite increased lymph flow.
• Permeability-surface area products for proteins were significantly higher with histamine, indicating increased permeability.

Conclusions:

• Histamine increases pulmonary vascular permeability to proteins.
• The observed effects suggest histamine is a potential mediator of increased lung vascular permeability.
• The impact on lung vessel porosity is more modest compared to systemic microvessels.