Chromosomal Changes in Rat Thyroid Cells during Iodine Depletion and Repletion¹

Chromosomal analyses of the thyroid cells of 72 inbred Fischer rats are reported here. Twenty-one rats fed an adequate iodine diet, were sacrificed in groups of 2–3 at 0.5- to 1-month intervals; their thyroid gland cells were grown in tissue culture and prepared for chromosome analyses. All but 1 had nonmodal chromosomal complements of 0–6% and no other abnormalities. Forty-one rats were fed Remington low-iodine diet for 0.5–6 months and sacrificed in groups of 2–4 at 0.5-month intervals; their thyroid cells were grown in tissue culture for chromosomal analyses. Chromosomal abnormalities were detected when thyroid hyperplasia was recognized. At 1–2.5 months of iodine deciency, 19–30% of the thyroid cells had a nonmodal number of chromosomes. The hyperdiploid cells were more numerous than the hypodiploids at this stage. The number of nonmodal cells was 30–44% at 3–6 months of iodine deficiency, but the hypodiploid cells were more numerous than the hyperdiploids at this interval. Marker chromosomes and structural abnormalities appeared at this late interval.

Ten rats were started on iodine repletion after 3 months of iodine deficiency; 6 were sacrificed at 1 month of repletion and 4 at 2 months; their thyroid cells were prepared for chromosomal analyses in the same way as the cells of the other rats. At 3 months of iodine deficiency, 33–36% of the thyroid cells were nonmodal; at 1 month of repletion 22% were nonmodal; and at 2 months of repletion 17% were nonmodal. The modal number of a transplanted thyroid tumor has shifted to 43, with several types of marker chromosomes.