Effect of lithium on thyroidal ¹³¹iodine uptake, its clearance, and circulating levels of triiodothyronine and thyroxine in lead-treated rats

Abstract 

The influence of lead acetate (50 mg per kg body weight) on the ¹³¹iodine (¹³¹I) biokinetics (uptake and retention) in rat thyroid and serum levels of triiodothyronine (T₃) as well as thyroxine (T₄) was evaluated as a function of time and in combination with lithium treatment. The 2-h and 24-h uptake of ¹³¹I in the thyroid was stimulated significantly by lead treatment. The 24-h uptake showed a maximum stimulation after 4 months of lead treatment. Lithium supplementation, however, showed the opposite effect by reducing the iodine uptake, whereby the maximum decrease was noticed after 2 months of treatment. Further, simultaneous lead and lithium treatment resulted in an even more pronounced increase of 2-h ¹³¹I uptake with a maximum after 3 months. However, the 24-h uptake after 3 months and 4 months of treatment did not differ significantly from the lead treated reference groups. The thyroidal biological half-life of ¹³¹I (T_biol) was found to have clearly increased following the lead/lithium treatment. Interestingly, the combined lead/lithium treatment applied for 4 months caused a further growth of T_biol, thus reflecting an increased retention of ¹³¹I. A maximum increase of T_biol was seen after 2 months of combined treatment. A progressive decline of the circulating T₃ and T₄ levels following lead or lithium treatment was noticed and was more pronounced after combined treatment.