[Thyroid hormones in rats receiving increasing doses of lithium]

Thyroid hormones were determined in rat serum, thyroid, liver and kidney tissues; the animals were fed for 40 days an equilibrate diet and various amounts of lithium carbonate were added to drinks. Serum lithium levels were related to their absorption. There was no change in rats drinking 300 mg Li2CO3/l solution for 5 weeks or 600 mg/l for 2 weeks, when compared to control rats. But 600 mg/l solutions for 5 weeks led to hormone increase in thyroid tissue. With 1200 mg/l acute hormonal decrease was seen in serum (thyroxine, T4: 3.2 micrograms/dl and control: 4, triiodothyronine T3: 54.8 ng/dl and control: 64) in liver tissue T3: 2.6 ng/g and control: 3.5), and in kidney tissue (T3: 4.8 ng/g and control: 6.4). In some animals receiving 600 or 1200 mg, lithium concentration was very high, body weights were very much reduced and there was large hormonal decrease in serum (T4: 1.4 micrograms/dl, T3: 48.5 ng/dl) in liver tissue (T4: 10.5 ng/g and control: 20.7; T3: 2.1 ng/g) and in kidney tissue (T4: 6.9 ng/g and control: 13.5 and T3: 3.3 ng/g). Hormonal changes were parallel to tubular kidney damage. These results are similar to those described in patients receiving lithium treatment.