Studies on vascular permeability. I. Description and evaluation of methods.

Three methods for assessing the extravasation of serum albumin in tissues (skin) and intended to demonstrate increased vascular permeability (IVP) in (immunopathological) inflammation sites have been compared. The radioassay (extravasated I-serum albumin counting) gave the values theoretically expected and was chosen as the reference technique. Two colorimetric techniques based on extravasation of Evans' blue bound to endogenous serum albumin were compared with it at cutaneous sites in which the vascular permeability had been increased by graded histamine reactions and delayed hypersensitivity reactions. The first technique makes use of a densitometer and has been found more precise than the second. A correlation curve was established between extravasated blue serum albumin (densitometric units) and extravasated radiolabelled serum albumin (c.p.m.). The second technique assesses the area of the blue spot, and the concentration of blue (by naked eye comparison with a carefully prepared and calibrated reference skin). It was found to be reliable and reasonably satisfactory, especially for studies including a great number of IVP sites.