Zinc sulphate following the administration of iodine-131 on the regulation of thyroid function, in rats.

Hyperthyroidism in men is often treated with high doses of iodine-131 ((131)I), which may induce radiation side effects to patients and their environment. These therapeutic doses of (131)I could be decreased, if the (131)I uptake of the thyroid gland of the patients could be increased. Zinc sulphate has been considered to exercise a protective role by maintaining the cellular integrity of the thyroid under various pathological states. The aim of our study was to study in Wistar rats whether zinc sulphate can after treatment of the thyroid gland with (131)I: a) increase the uptake of (131)I in the thyroid and b) stabilize the function of the follicular cells. If such a stabilization finally exists in men we could have favorable results like fewer cases of hypothyroidism after (131)I treatment of hyperthyroidism. To carry out these investigations, rats were divided into four groups comprising of eight animals each. Group I animals served as normal controls. Group II animals received a dose of 3.7 MBq of (131)I. Group III animals were supplemented with zinc (227 mg/L of drinking water) and animals in Group IV were given (131)I together with zinc sulphate as above. Our results showed that in Group II, serum levels of tetra-iodo-thyronine (T(4)) and tri-iodo-thyronine (T(3)) decreased significantly as a function of time following (131)I treatment. An increase in the levels of serum thyroid stimulating hormone (TSH) was noticed one week after (131)I treatment, becoming less pronounced with time. In Group II, thyroid uptake at 2h and at 24h was significantly decreased. In the same Group biological half life (T(biol)) of (131)I in the thyroid gland, was significantly elevated four weeks after the administration of (131)I and decreased eight weeks after. In Group IV animals, zinc sulfate after four weeks, induced normalization of elevated serum TSH levels and a further increase in the T(biol) of (131)I. After eight weeks in these animals, serum T(3) became normal and TSH remained at normal levels. Thyroid (131)I uptake at 2 and 24 h was increased as compared to Group II. Group III animals showed some increase in the levels of Na(+)K(+)ATPase and type 1,5'-deiodinase (5'-DI) as compared to normal rats of Group I. In conclusion, this study suggests the protective potential of zinc sulphate in the disturbed after (131)I treatment, thyroid function, thyroid hormones and TSH while the (131)I uptake was reduced. Thus, if this result is further confirmed, zinc sulphate may show to be a promising radioprotective agent for the thyroid gland.