Influence of zinc on the biokinetics of I-131 and thyroid functions following lithium therapy

Objectives The present study was designed to explore the potential of zinc in regulating ¹³¹I biokinetics and thyroid functions following lithium therapy.

Methods Female sprague dawley rats weighing 110-140g were segregated into four groups viz. Group I-untreated controls, Group II(lithium treated- Li₂CO₃-1.1 g/kg diet), Group III(zinc treated-227 mg ZnSO₄/L drinking water) and Group IV(combined treated). The treatments were given for time durations of 1, 2 and 4 months.

Results Following intraperitoneal administration of 0.37 MBq carrier- free-¹³¹I, a significant depression in the thyroidal ¹³¹I uptake both at 2 and 24 hrs was observed following lithium treatment for all the durations which however was normalized following zinc treatment. Lithium treatment caused a significant elevation in the thyroidal biological half life of ¹³¹I which was attenuated following 2 and 4 months of zinc supplementation. Lithium supplementation for 2 and 4 months significantly decreased serum T₃ and T₄ levels which however were increased following zinc treatment. Lithium treatment for 4 months caused a significant decrease in the thyroidal activities of Na⁺ K⁺ ATPase and monoamine oxidase which were nearly normalized by zinc. Further, lithium treatment for 4 months raised thyroidal levels of lipid peroxidation and catalase which however were normalized by zinc. On the contrary, thyroidal levels of reduced glutathione and glutathione S transferase decreased significantly following 2 and 4 months of lithium treatment but were significantly increased by zinc.

Conclusions The present study concludes that zinc supplementation is helpful in attenuating the adverse effects caused by lithium on thyroid functions and can effectively regulate the biokinetics of ¹³¹I following lithium therapy.