Journal of Applied Physiology, Vol 52, Issue 3 585-590, Copyright © 1982 by American Physiological Society
Restricted dextran transport in the sheep lung lymph preparation
J. E. McNamee
The ease with which plasma proteins and other large solutes enter sheep
lung lymph had led previous investigators to conclude that such large
molecules probably move through a pathway that has transport properties
similar to pores 100 nm or larger in radius. To test this hypothesis, the
transport of some very large solutes into lung lymph was measured. Dextran
fractions having Stokes-Einstein radii of 10--150 nm were prepared and
labeled with fluorescein isothiocyanate (FITC). Five sheep were given
2--2.5 g FITC-dextran 24--36 h prior to cannulation of the efferent duct of
the caudal mediastinal lymph node. Analysis of paired plasma and lymph
samples for fluorescence as a function of molecular size gave the following
results. FITC-dextran 10 nm in radius appeared in sheep lung lymph at 0.30
+/- 0.06 of its plasma concentration. Larger FITC-dextran molecules
appeared at still lower concentrations until, above 35 nm, fluorescence
could no longer be detected in lymph. The restriction to transport of
FITC-dextran was found to be inconsistent with values predicted by a pore
pathway 100 nm or larger. These data are compatible with a pore pathway
22--35 nm in radius.
