Shin-Ichi Shimoda

Further studies on the mechanism of action of trypan blue and related dyes in suppressing thyroid activity in the rat

Abstract Mechanism of action of trypan blue and related diazo dyes in suppressing thyroid activity was studied in the rat. Five dyes tested had variable effects on thyroidal radioiodine uptake; EB had the greatest effect, NB2B no effect, the others intermediate. This decrease of thyroidal radioiodine uptake corresponded roughly to the decrease in serum PBI. Six dyes all augmented in vitro uptake of labeled T4 by human red blood cell in dilute rat plasma, but there was no correlation between the in vivo thyroid suppressing activities of the dyes and their in vitro T4 displacing effects. However, when plasma from dye injected animals was used, there was a correlation between the amounts of T4 available to the red blood cell and dye effect on thyroid activity. By utilizing muscle, liver and pituitary, this dye effect was also produced. It is concluded that the primary effect of diazo dyes on the thyroid is to inhibit TSH release by displacing T4 from the binding sites of plasma proteins. Unlike T4, T3 uptake by the red blood cell did not change or its uptake by the muscle and liver decrease significantly under the influence of diazo dyes. Although a physiologic significance of this apparent difference between T4 and T3 is not known, the mode of action of diaze dyes in displacing thyroid hormones from the plasma is somewhat different from that of several drugs reported by others.

IN VITRO FORMATION OF FREE IODOTYROSINES AND IODOTHYRONINES BY RAT THYROID LOBES OR ISOLATED FOLLICULAR CELLS.

Summary Free radioiodinated amino acids are released into the medium during a 3- to 6-hour period of incubation with 131I of intact thyroid lobes from severely iodine-deficient rats or of isolated beef thyroid follicular cells. MIT and DIT are found in the medium primarily in peptide-bound form, but T4 and T3 are apparently found only as free amino acids. T4 enters the medium more readily than T3.