Thiouracil Modification of Effect of Radioiodine (I131) on the Thyroid

Publisher Website
Google Scholar
Abstract
The rather thorough destruction of the thyroid gland by injection of experimental animals with large doses of radioiodine has been demonstrated by Reinhardt (37), Leblond (28), Chapman (9), Findlay and Leblond (13), Gorbman (18), Chaikoff and Taurog (8), Freedberg and Kurland (14), Winchester, Comar, and Davis (46), Shapiro (41), and Rugh (38, 39). It is of interest to determine whether the histologic reaction of the intact thyroid to injected radioiodine might be altered by pretreatment of the animal with one of the antithyroid compounds, namely thiouracil. The salamander, Triturus pyrrhogaster, was chosen because it has a relatively low metabolic rate and any changes that occur could be studied over an extended period. A further advantage is the fact that the constituent cells of the amphibia are among the largest and the most satisfactory for study in the entire animal kingdom. Materials and Method The specimens of Triturus pyrrhogaster, the Japanese fire salamander, had been kept under laboratory conditions for over a year. Fully grown, sexually mature females weighing at least 8 gm. were selected for this study. The animals were maintained at a constant temperature of 15° C., in tap water, and were fed raw liver once each week. The thiouracil was received from Parke, Davis and Co. in powder form and was used in a 1 per cent suspension in saline. It was injected intraperitoneally on days 1, 4, 6, and 20. Since 10 mg. of the drug were injected each time, over the three-week period, each of the salamanders thus treated received a total of 40 mg. of the antithyroid substance. The radioiodine was received directly from the pile at Oak Ridge and was in the form of carrier-free sodium iodide (NaI131). It was diluted with distilled water so that the final concentration was 100 μc.∕c.c. A single intraperitoneal injection of 0.25 c.c, —25 μc. of radioiodine—was given some of the experimental animals on the twenty-second day following the first injection of the thiouracil. The observation period began as of the day the I131 injection was made, the thiouracil-treated animals having had a pretreatment with the antithyroid drug of three full weeks. A total of 48 salamanders was involved in these experiments, divided into four groups as follows: 12 controls, 12 treated with thiouracil, 12 treated with radioiodine, and 12 treated with thiouracil followed by radioiodine injection. At intervals of one week, one month, two months, and seven months, 3 animals from each of the above groups were sacrificed. The thyroid and the anterior pituitary glands were preserved in Bouin's fluid and subsequently sectioned at 5 microns and stained with Masson trichrome stain or Delafield's hematoxylin.