RESUMO
Lithium salts are being used increasingly to treat patient with affective disorders, especially acute mania, or bipolar manic-depressive illness. For therapeutic effect the lithium content must be maintained at or above a particular level. Lithium poisoning due to overdosage may be seen occasionally, and its course is determined primarily by the rate of renal lithium elimination. A search is therefore indicated for procedures that could raise the lithium clearance. In a number of reports renal lithium excretion has been studied in relation to the excretion of water, sodium, potassium and hydrogen, but effects of sodium or water on the lithium excretion has not yet been clarified. Hence the present study was undertaken to investigate the effects of corticosteroid on the excretion of lithium ion. The female rat (Sprague-Dowley), weighing from 200 to 300g, was injected with 50mg/kg of lithium chloride intraperitoneally, and then injected with graded dosage of fludrocortisones and dexamethasone in each group. During the injected rats were incubated in metabolic cage, 24 hour urine of rats were collected. At 24 hours after injection, the rats were sacrificed with guillotine, the blood were collected. And then the concentrations of Na⁺, K⁺, Li⁺ of collected urine and serum were checked by Flame photometer. The results are summarized as follows 1. Fludrocortisone decreased the serum concentration of lithium and increased the urinary excretion of lithium. 2. In the group treated with low dose of dexamethasone (0.1 mg/kg), the serum concentration of lithium was decreased and high dose of dexamethasone (1 mg/kg) increased the urinary excretion of lithium. 3. Fludrocortisone increased the urinary [Na⁺]/[K⁺] in serum and decreased [Na⁺]/[K⁺] inurine, but opposite effects were occurred in dexamethasone. By above results, it may be concluded that corticosteroid increased the urinary excretion of lithium and decreased the serum concentration of lithium, but it seems to be there in no relationship between these effects of corticosteroid and of the renal Na⁺ or K⁺ transport.