Thyroid and pituitary thyroxine-5′-deiodinase activity and thyrotrophin secretion in lithium-treated rats

Abstract

Some authors have reported increased serum thyrotrophin (TSH) in animals chronically treated with lithium, suggesting that lithium might decrease pituitary thyroxine (T4)-5′-deiodinase activity. On the other hand, the effect of lithium treatment on thyroidal T4-5′-deiodinase activity is also unknown. The present study was undertaken to evaluate the effects of lithium treatment on pituitary and thyroid T4-5′-deiodinase activity. Serum and pituitary TSH levels and thyroidal and pituitary T4-5′-deiodinase activities were determined in 3-month-old isogenic male Dutch-Miranda rats treated with lithium for 8 weeks. Chronic lithium treatment produced a slight increase in pituitary TSH content, but no change in serum TSH, and a significant increase in the thyroidal T4-5′-deiodinase activity. However, the pituitary T4-5′-deiodinase activity was unaffected by lithium administration. As far as we know, the present data show for the first time that chronic lithium treatment can increase the thyroxine to triiodothyronine conversion in the murine thyroid gland, be it directly or indirectly.