Figure 3.

The extent of thyroidal radioiodine accumulation and temporal duration of NIS-mediated thyroidal Na^99mTcO₄ influx activity induced by bTSH is less in Tg-PTC1 mice than that in wild-type mice. (A) Seven-month-old WT and 4-month-old Tg-PTC1 mice were given 12 μg/ml T₃ in drinking water daily. On day 5, mice were injected with either one dose of 60 or 90 μg bTSH. Na¹²³I (20–40 μCi) was injected into the mice at 16 h post bTSH injection. At 6 h (t6) post Na¹²³I injection, mice were euthanized and thyroids were harvested and subjected for counting of activity by a γ counter. Statistical analysis showed that WT mice had significantly higher (P value=0.001) thyroidal radioiodine accumulation at t6 than Tg-PTC1 mice, while there was no significant difference (P value=0.71) between 60 and 90 μg bTSH-induced thyroidal radioiodine accumulation in both WT and Tg-PTC1 mice. (B) T₃-supplemented WT and Tg-PTC1 mice were administered with one dose of 60 μg bTSH. Na^99mTcO₄ (100 μCi), a substrate of NIS yet could not be organified by thyroid, was first injected into mice 16 h post bTSH injection and SPECT images were acquired at 1 h post Na^99mTcO₄ injection, i.e. at 17 h post bTSH injection. A second dose of Na^99mTcO₄ (100 μCi) was injected into mice 40 h post bTSH injection and SPECT images were acquired at 1 h post the second Na^99mTcO₄ injection, i.e. at 41 h post bTSH injection. Two out of three WT mice had comparable NIS-mediated ^99mTcO₄ influx activity at the two different time points, whereas all three Tg-PTC1 mice had decreased NIS-mediated ^99mTcO₄ influx activity at later time point. The difference in duration of NIS-mediated thyroidal ^99mTcO₄ influx activity induced by single dose of bTSH between Tg-PTC1 mice and WT mice was statistically significant (P value=0.014).