EVIDENCE OF ACTIVE TRANSPORT (FILTRATION?) OF PLASMA PROTEINS ACROSS THE CAPILLARY WALLS IN MUSCLE AND SUBCUTIS*

Abstract

Under slight lymphatic stasis (tilting the body 15°)

we measured the arrival of locally injected ¹³¹I-albu-

min to the plasma pool. From 30 min. to 90 min.

after the injection the return rate was zero i.e. local

back transport in the two tissues studied viz.muscle

and subcutaneous fat is very small.

Compared to a suggested steady state total ¹³¹I-albu-

min clearance of 1.7%/hour in the horizontal body

position we conclude that maximally one percent of

the interstitial albumin can have a local transendothe-

tial escape i.e. can be handled by passive forces as is

diffusion and pinocytosis. As passive flux is proportional

to the concentration and the interstitial albumin

concentration is about half the plasma concentration

then also diffusion and or pinocytosis from the

plasma of albumin is negligible in the resting normal

man. We suggest filtration through big leaks as the

main mechanism for transendothelial protein transport.