EFFECT OF PTU ADDED TO A LOW IODINE DIET ON PEROXIDASE-ACTIVITY AND OTHER PARAMETERS OF THYROID-FUNCTION IN RATS

The evolution of peroxidase activity was followed in relation to other parameters of thyroid function in rats when PTU was added to a low iodine diet (LID). Ten days of PTU treatment brings about an equivalent increase in thyroid weight and iodide peroxidase activity at whatever time PTU was added to LID (10, 35, 54 and 50 days). It is shown that the effect of PTU treatment on thyroid weight and peroxidase activity is proportionately higher when PTU ia added after 10 days of LUD alone than after 80 days. The effect of various durations of PTU treatment was studied more closely when the addition began on day 10 of LID. On day 1 after addition of PTU thyroid weight increased significantly and no significant change was found in peroxidase activity. In contrast 5 days of PTU induced a significant elevation in enzymatic activity which is greater than that of thyroid weight. For a longer period of PTU treatment (10 days or more), the percent increase of thyroid weight and peroxidase activity evolved parallely. Already on day 1 of PTU treatment very rapid change were noted on T4, T3 and TSH levels; there was a decrease in T3 level (26 ± 5.6%), while an increase in T4 level (26.4± 4.7%) and TSH level (30 ± 5%) was observed when the iodine content was still high (about 11 μg/thyroid gland). Thereafter T3 and T4 decreased and stayed at the same level after 10 days of PTU, while TSH increased rapidly and reached a plateau between 18 and 35 days. When PTU was added to LID treatment the increase in TSH was mostly due to a decrease of T3. The percent increase in serum TSH level is always higher than that of thyroid peroxidase activity.