Influence of age on thyroidal 131I uptake in Beagle pups

Parameters in radioiodine metabolism by the thyroid gland were investigated in 98 beagle pups 0-110 da of age and in 6 adults. Significant age-related differences in thyroidal 131I uptake, uptake/g of thyroid, and retention and subsequent radiation dose were observed. Significant differences were also found in uptake/g, retention and subsequent radiation dose were observed. Significant differences were also found in uptake/g, retention, and dose between litters of the same age. Seventy-da-old pups had the highest mean uptake (approximately 25% of the administered dose) and fastest release rate (effective half-life approximately 3.6 da), whereas neonates less than 12 hr of age showed the highest peak concentration (157% of administered dose/g thyroid). The calculated radiation doses to the thyroid were highest in newborn pups, averaging over 100 rads per microcurie of 131I administered, or about 10 times the dose/muCi for adults.