Evidence of active transport (filtration?) of plasma proteins across the capillary walls in muscle and subcutis.

Under slight lymphatic stasis (tilting the body 15 degrees) we measured the arrival of locally injected I-albumin 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 131 I-albumin clearance of 1.7%/hour in the horizontal body position we conclude that maximally one percent of the interstitial albumin can have a local transendothetial 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 comcentration is about half the plasma concentration then also diffusion and or pinocytosis from the plasma of albumin is negligble in the resting normal man. We suggest filtration through big leaks as the main mechanism for transendothelial protein transport.