Pulmonary capillary permeability to HRP in dogs: a physiological and morphological study

Area of Science:

• Pulmonary Physiology
• Vascular Biology
• Cellular Biology

Background:

• Pulmonary capillary permeability is crucial for maintaining lung fluid balance.
• Understanding the mechanisms of macromolecule passage across pulmonary capillaries is essential.
• Horseradish peroxidase (HRP) is a commonly used tracer for studying vascular permeability.

Purpose of the Study:

• To investigate pulmonary capillary permeability in normal anesthetized dogs.
• To determine the passage of horseradish peroxidase (HRP) across pulmonary capillaries.
• To elucidate the pathways involved in HRP translocation.

Main Methods:

• Measurement of hemodynamic parameters (left ventricular, pulmonary arterial, wedge pressures).
• Collection and analysis of right lymphatic duct (RLD) and thoracic duct lymph.
• Intravenous administration of HRP at varying doses and colorimetric quantification in plasma and lymph.
• Electron microscopy and freeze-cleaving studies to visualize HRP passage and junctional complexes.

Main Results:

• HRP was detected in RLD lymph at all administered dose levels.
• Electron microscopy confirmed HRP passage across pulmonary capillaries under normal physiological conditions.
• Freeze-cleaving suggested HRP translocation occurs via interendothelial pathways, possibly due to tight junction discontinuities.

Conclusions:

• Pulmonary capillaries permit the passage of macromolecules like HRP under normal physiological conditions.
• Discontinuities in the junctional strands of tight junctions may represent pathways for macromolecule transport.
• This study provides insights into the structural basis of pulmonary capillary permeability.