Uptake of ³H-labelled commercial toluidine blue and subfractions (thionine, toluidine blue, and azur A) in the parathyroids of rabbits.

Chromatographic separation of ³H-labelled commercial toluidine blue demonstrated four dye fractions. Following i.v. injection into rabbits, the uptakes of the dye mixture and of three separated dye fractions were determined by radioactivity assays of parathyroids, thyroid, and muscle. Mean uptake ratio per g parathyroid/thyroid of the dye mixture was 2.6 and of the different fractions varied from 2.2 to 2.7. During continuous infusion of labelled dye mixture, the concentration in the parathyroids was, on an average, 1.6 times that in the thyroids. It follows that as a means for external scintigraphy of the parathyroids, derivatives of dye fraction will probably not prove better than derivatives of the commercial dye mixture. Because of its high toxicity, thionine should be eliminated from commercial toluidine blue when given to patients in amounts necessary to stain the parathyroids.