A Purified Fraction of Thioflavine-S (Vasoflavine): Valuable Agent for Visualization of Blood Vessels.

Abstract

Thioflavine-S, a fluorescent dye, has provided a new medium for the visualization of blood vessels under more physiological conditions than heretofore. It has a definite affinity for the vessel walls and is retained there sufficiently long to allow for removal of the organ, and examination under u.-v. light. There seemed to be two fractions in this dye, one which was retained by the vessel walls and imparted to them a yellowish-green fluorescence, and another which diffused out of the vessels rapidly and imparted to the surrounding tissues a bluish fluorescence. A water extract of a more highly purified commercial Thioflavine-S (Erie-flavine-S, concn. 130% ) was more suitable from the standpoint of greater fluorescence and less diffusion out of the vessels. An attempt was made to determine the character of this substance by paper chromatography, dialysis, and spec-trophotometry. The evidence pointed to the following conclusions: (1) The solution of dye probably exists as an equilibrium between monomeric and polymeric forms. (2) The yellow-green fluorescence is apparently produced by the higher forms and the bluish by the monomeric form. (3) The higher the concn. of an aqueous soln. of the dye the more of the polymeric forms exist. (4) The polymers are probably too large in molecular size to pass the vessel walls readily, while the monomeric form diffuses rapidly out of the vessels.