125I uptake and organification

At postnatal day 8, mothers and litters were fed with an iodine-free diet for 24 hours. At postnatal day 9 (P9), pups were injected intraperitoneally with 1 μCi ¹²⁵I (Perkin Elmer) and left for another 24 hours before sacrifice and thyroid dissection. Both lobes were collected in 2 mM methimazole (Sigma) and homogenized with a glass Potter. Total thyroid ¹²⁵I was measured with an automatic gamma counter “Wizard²” (Perkin Elmer) before protein precipitation using 10% trichloroacetic acid (TCA; Merck). After a single wash in TCA, radioactivity was measured in the protein pellet. Percentage of protein-bound iodide was calculated using the ratio of precipitated cpm/total thyroid cpm (27).