Kinetics of Vascular and Extravascular Protein Exchange in Unbled and Bled Dogs

¹ From the Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana

Unanesthetized, healthy greyhounds were infused with 25% albumin or bled, injected with I¹³¹-labeled albumin and albumin specific activities determined. It is shown that the albumin specific activity curves can be altered by changing the ratio of the vascular to extravascular albumin masses in a manner predicted from the mathematics of a two-compartment system. Increase of vascular albumin mass relative to extravascular mass results in a smaller initial disappearance of albumin specific activity from the blood stream and a faster approach to equilibrium. Decrease of vascular albumin mass relative to extravascular mass by bleeding shows that 50% of albumin replacement after hemorrhage appears to be accomplished within 24 hours. Almost all of this protein comes from the extravascular compartment. Rapid anabolism accounts for the replenishment of protein for the next 2–5 days, during and after which there is a reduced catabolism of the existing plasma albumin. The results indicate that an extravascular albumin mass exists as a separate entity and net movements may occur from this mass into the plasma when the equilibrium between the vascular and extravascular masses is disturbed.