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Restricted dextran transport in the sheep lung lymph preparation
Summary
Researchers studied large molecule transport in sheep lungs. Findings suggest lung lymph pathways are smaller, around 22-35 nm, not 100 nm as previously thought.
Area of Science:
- Pulmonary Physiology
- Lymphatic Transport
- Biophysics
Background:
- Previous studies suggested large pores (≥100 nm radius) in sheep lung lymphatics for protein transport.
- This hypothesis was based on the observed ease of entry for plasma proteins and large solutes.
Purpose of the Study:
- To investigate the transport of very large solutes into sheep lung lymph.
- To determine the size limitations of the lymphatic transport pathway in the lung.
Main Methods:
- Prepared fluorescein isothiocyanate (FITC)-labeled dextran fractions with radii from 10–150 nm.
- Administered FITC-dextran to five sheep and collected plasma and lung lymph samples.
- Analyzed fluorescence intensity in relation to molecular size in paired samples.
Main Results:
- FITC-dextran (10 nm radius) reached 30% of plasma concentration in lymph.
- Transport decreased significantly with increasing dextran size; no fluorescence detected above 35 nm radius.
- Observed transport restrictions were inconsistent with a ≥100 nm pore pathway.
Conclusions:
- The data contradict the existence of large pores (≥100 nm) in sheep lung lymphatics.
- The findings support a narrower pore pathway, estimated at 22–35 nm in radius.
- This study refines our understanding of macromolecule permeability in the pulmonary lymphatic system.