Combination of Evans blue with plasma protein; its significance in capillary permeability studies, blood dye disappearance curves, and its use as a protein tag.

The use of isotopes has proved to be an important tool in the study of the metlabolism of body constituents (1). The employment of such tracer substan,ces has developed an awareness for easily identifiable substances which can be combined with a particular body constituent, in order to tag it for study purposes. It is understandable, therefore, that the announcement by Rawson(2) that Evans blue dye (T-1824) combines selectively with the albumin of blood plasma would foster studies employing this dye as a tracer for serum albumin. Thus, for example, Cope and Moore (3) studied the problem of capillary permeability to albumin in burn shock utilizing radioactive dibromo Evans blue as a tracer for albumin. Evans blue dye (T-1824) has come into wide clinical use as a dyestuff suitable for determining blood volume. Gregersen and Rawson (4), in studies of the disappearance of T-1824 from the blood of dogs, observed that there was an early logarithmic phase of disappearance lasting for approximately one hour. This was followed by.a linear phase during which time the dye disappeared from the blood at a constant rate. In view of Rawson’s (2) demonstration that the dye combines selectively with albumin, the logarithmic phase of disappearance was considered as a measure of capillary permeability to albumin. Accordingly, its disappearance after the logarithmic phase would possibly mean that a definite quantity of albumin has been removed with the dye from the plasma. Since plasma protein concentration is maintained within narrow limits, that amount of dye-protein removed would have been replaced by protein uncombined with dye. From these considerations, the definite possibility exists that the rate of disappearance of dye from the blood stream would mirror the rate of albumin turnover in the body. The potentialities of this attractive idea for the development of a clinical test for quantitating albumin regeneration rates prompted US to explore this concept experimentally. It is known that basic dyestuffs accumulate in high concentrations in the juice of actively secreting stomachs (5, 6) and acid dyestuffs, in the alkaline pancreatic juice. In these. studies it has usually been considered that it was the permeability to the dye molecules alone which was being investigated. However, in the case of Evans blue, protein complex, whose chemical one and would be following the behavior of a dyephysical properties are necessarily different