A Purified Fraction of Thioflavine-S (Vasoflavine)

Summary and Conclusions

A more fluorescent and less rapidly diffusible dye with a strong affinity for the walls of the blood vessels has been described. This dye is a purified, water soluble fraction of Thioflavine-S and has been named Vasoflavine. Studies leading to a more accurate characterization of this dye are described. These include paper chromatography, dialysis, and spectrophotometry.

The following conclusions are offered: 1. Vasoflavine approaches the ideal dye for the visualization of blood vessels under ultraviolet light and is much superior to the Thioflavine-S previously used. 2. The solution of dye probably exists as an equilibrium between monomeric and various polymeric forms. 3. The higher the concentration of an aqueous solution of the dye the more of the polymeric forms exist. 4. The yellow-green fluorescence is apparently produced by the higher form and the bluish by the monomeric form. 5. The polymers are probably too large in molecular size to pass the barrier of the vessel walls readily, while the monomeric form quickly diffuses out of the vessels, thus explaining the yellow-green fluorescence of vessels and the bluish fluorescence of the surrounding tissue. It should be noted that Vasoflavine exhibits no apparent toxic effects in experimental animals (rats, rabbits, and dogs) in blood concentrations as high as 275 mg %percnt;, but extensive toxicity studies have not been carried out.