Effectiveness of zinc in regulating thyroid function following I-131 treatment to wistar rat

Studies were conducted to elucidate the role of zinc on status of thyroid hormones and TSH, as well as enzymes namely Na+/K+ ATPase, SOD (superoxide dismutase) and catalase related with oxidative stress. To carry out the investigation, 32 wistar rats were segregated into 4 groups viz normal control, I-131 treated, zinc controls and combined zinc + I-131 treated. All the rats were given diet and water ad libitum. Rats belonging to groups 2 and 4 were administered a dose of 37 Mbq of I-131(carrier free) intraperitoneally. Zinc (as ZnSO4.7H2O ) at a dose level of 227mg/L in drinking water, given to the rats belonging to groups 3 and 4. Blood samples were drawn, by ocular vein puncture under mild ether anesthesia at 1 and 4 week interval. 2 and 24 hr radioiodine thyroid uptake values were obtained following single intraperitoneal dose of 0.37 Mbq at 1st and 4th week interval. All the animals belonging to different groups were sacrificed after subjecting them to ether anesthesia at the end of a 4 week study, for the assessment of enzymes activities of Na+/K+ ATPase, SOD and Catalase. Significant decrease in 2 and 24hr I-131 uptake values were observed in animals belonging to groups 2 and 4. Interestingly, zinc supplementation alone showed a significant enhancement in 24 hr I-131 uptake values. The investigations also revealed a significant suppression in levels of T3 at 1st and 4th week, after I-131 administration to rats. However, the levels of T4 were found to be significantly depressed only after 4 week of I-131 administration. Interestingly Zinc supplementation to normal rats resulted in significant elevation of T4 levels after 4 weeks. Further rats receiving combined zinc + I-131 treatment also showed a significant elevation in T4 levels. The levels of TSH were significantly elevated after 1st week of I-131 administration to normal rats, but were within normal limits after 4 weeks of its administration. Interestingly, zinc supplementation also lead to a significant increase in the concentration of TSH, after 1 week of its administration. The study also revealed that the TSH levels which were significantly high after both the time intervals were significantly reduced following zinc administration to I-131 treated rats. SOD levels were significantly depressed in the I-131 treated group. Interestingly, zinc supplementation alone showed significant rise in activities of SOD. However, the SOD values were brought to within normal limits by zinc supplementation to I-131 treated group.Activities of Na+/k+ ATPase levels were found to be significantly decreased following I-131 treatment, thus substantiating the depressed thyroidal I-131 uptake values. On the contrary, Zn supplementation has shown increase of Na+/K+ ATPase activities as compared with I-131 treated group. There was no change in Catalase activities in rat treated with I-131, when compared to normal rat. However, zinc supplementation alone showed significant rise in catalase activity. Conclusion - Hence the present study reveals that zinc is able to restore some of the thyroid functions affected by I-131 treatment