Radioactive iodide ( 131I ？) protection studies have focused primarily on the thyroid gland and disturbances in the hypothalamic-pituitary-thyroid axis. The objective of the current study was to establish 131I ？ urinary excretion profiles for saline, and the thyroid protectants, potassium iodide (KI) and ammonium perchlorate over a 75 hour time-course. Rats were administered 131I ？ and 3 hours later dosed with either saline, 30 mg/kg of NH 4ClO 4 or 30 mg/kg of KI. Urinalysis of the first 36 hours of the time-course revealed that NH 4ClO 4 treated animals excreted significantly more 131I ？ compared with KI and saline treatments. A second study followed the same protocol, but thyroxine (T 4) was administered daily over a 3 day period. During the first 6–12 hour after 131I ？ dosing, rats administered NH 4ClO 4 excreted significantly more 131I ？ than the other treatment groups. T 4 treatment resulted in increased retention of radioiodide in the thyroid gland 75 hour after 131I ？ administration. We speculate that the T 4 treatment related reduction in serum TSH caused a decrease synthesis and secretion of thyroid hormones resulting in greater residual radioiodide in the thyroid gland. Our findings suggest that ammonium perchlorate treatment accelerates the elimination rate of radioiodide within the first 24 to 36 hours and thus may be more effective at reducing harmful exposure to 131I ？ compared to KI treatment for repeated dosing situations. Repeated dosing studies are needed to compare the effectiveness of these treatments to reduce the radioactive iodide burden of the thyroid gland.
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