Intra- and extravascular distribution of albumin and immunoglobulin in man.

The plasma proteins are constantly shuttling between intravascular and extravascular mass of a specific plasma protein is determined by its individual rate of synthesis and the mean total time it spends in plasma. The ratio of intravascular to total mass (distribution ratio) is determined by the relative rate, at which it passes from plasma to interstitial spaces (transcapillary escape rate: TER) and the relative return rate via lymph. TER in a specific organ depends on the local leakiness of the microvasculature. The overall value in normal man varies with the molecular weight of the protein being about 5%/h of the intravascular albumin mass, 3%/h for IgG and less than 1%/h for IgM. The higher the TER, the lower is the intravascular fraction. Hypertension, diabetes mellitus, burns, myxedema and certain types of liver cirrhosis will increase TER. In hypertension and diabetes this may be compensated for by an increased lymphatic return rate. Hypoproteinemia due to malnutrition or urinary or gastrointestinal loss is accompanied by a shift from the extravascular to the intravascular space.