Restoration of thyroid function after total thyroidectomy and quantitative thyroid cell transplantation

Abstract

Quantitative thyroid cell transplantation was used to evaluate the reestablishment of thyroid function in surgically thyroidectomized rats. Donor thyroid glands were enzymatically dispersed, and the cells were quantified, serially diluted, and inoculated into the sc fat pads of syngeneic recipient rats 1 day after surgical thyroidectomy. Blood samples were obtained weekly, and serum T3, T4, and TSH levels were determined by RIA. Recipient rats displayed different patterns of restoration of thyroid function depending on 1) the number of thyroid cells inoculated and 2) their dietary iodine intake. We observed cell dose-dependent differences in both the rapidity and extent of thyroid function after cell transplantation. Recipients fed a normal diet and grafted with 6 × 104 or more cells reached near-normal levels of all three hormones. In recipients fed a low iodine diet, T4 and TSH levels remained at significantly hypothyroid levels for the duration of the 7-week study. At the highest cell dose examined (3 × 105), however, serum TSH levels began to decline by the sixth to seventh week. In spite of the iodine deficiency, recovery of T3 levels in these recipients paralleled that in recipients fed normal diets. Intact control animals exhibited the anticipated pattern of decreased T4, increased TSH, and essentially unchanged T3. 125I uptake by the grafts was also dependent on the initial number of thyroid cells grafted independent of diet.