Наука и Здравоохранение

Background: Human thyroid gland is generally regarded as a relatively low-risk organ in terms of developing radiation-induced tumorigenesis. However, a rapid increase in the incidents of thyroid cancer after the Chernobyl nuclear reactor accident in 1986 provided additional insight into the risk of thyroid cancer. Three key risk factors have been identified to be involved in this increase: (1) internal irradiation from ¹³¹I fallout, (2) young age, and (3) a low-iodine diet. Our previous study demonstrated that the thyroid radiation dose was highest in the newborn rats fed with low-iodine diet when rats of varying ages were internally exposed to ¹³¹I at the same radioactivity per body weight.

Objective: To examine the short-term effects of a low dose internal irradiation of ¹³¹I on the status of the thyroid hormone in rats of three different ages maintained on either standard diet or low-iodine diet.

Methods: ¹³¹I was injected intraperitoneally in F344 rats at the ages of 1, 4, and 9 weeks. Animals were maintained with an iodine-deficient (IDD) or a standard (SD) diet. Changes in serum levels of triiodothyronine (T₃), thyroxine (T₄), and thyroid-stimulating hormone (TSH) were examined.

Results: Dramatic changes in hormone levels were found only in the rats belonging to 1-week-old IDD group, in which T₃ levels rapidly dropped and TSH levels increased after ¹³¹I irradiation, whereas they remained unchanged in the SD group. In 4- and 9-week-old rats, hormone levels were also steady after irradiation, with no differences between the IDD and SD groups.

Conclusions: These data suggest that under low-iodine conditions, the status of thyroid hormone of newborn rats is particularly sensitive to internal irradiation of ¹³¹I.