FD-AND-C RED NO-105 (ROSE-BENGAL-B) NEUTRALIZES THE THYROID-TUMOR PROMOTING EFFECT OF IODINE-DEFICIENT DIET IN RATS

The effect of 3,4,5,6-tetrachloro-2',4',5',7' -tetraiodo-fluorescein s odium salt (Rose Bengal B or FDandC Red No.105, molecular weight 1017. 6) on the thyroid of rats treated with N-bis(2-hydroxypropyl)-nitrosam ine (DHPN) and iodine-deficient (I-def) diet is studied. Six-week-old male F344 rats were divided into seven groups (20 each) and given a si ngle subcutaneous injection of DHPN (2800 mg/kg body wt.). From week 2 to 20, I-def diet was given in combination with either FR105 (1.25, 5 .0, or 20 mg/l) or potassium iodide (KI, 12.5, 50.0 or 200 mu g/l) in drinking water. As a result, an amount of 1.25 mg/l of FR105 was sligh tly more effective than 200 mu g/l of KI in terms of inhibition of the effect of I-def diet on thyroid weight, morphology, thyroid-related h ormones and thyroid tumor development. It was calculated that 1 mu mol /l of FR 105 was slightly more potent than 1 mu mol/l of iodide ion. A s each FR105 molecule has four iodide residues, at least 25% of total iodide residues were calculated to be utilized by the rats given I-def diet,