Lithium-Induced Polyuria in Rats

Abstract

Rats given lithium with the fodder in a dosage of about 1 mEq/day/kg body weight developed a pronounced polyuria, which remained stable for months. The serum lithium concentration remained around 0.7 mEq/1, and the animals were, apart from reduced weight gain, unaffected by the treatment. The polyuria did not respond to the administration of vasopressin; it was accordingly of renal and not of pituitary origin. Small changes in serum and tissue electrolytes were presumably secondary to the increased urine flow. Creatinine and lithium clearances were unchanged. The lithium-induced polyuria was fully reversible; after discontinuation of lithium, urine flows fell to normal values within 5-8 days. Administration of lithium in a higher dosage (about 1.5 mEq/day/kg) also led to the development of polyuria, but after a few weeks the condition became unstable. The urine flow started to fall, and serum lithium, which had been around 1.1 mEq/1, started to rise. On continued lithium administration the rats would eventually die, but on discontinuation the condition was fully reversible until shortly before death.§