Functional and structural changes in the rat kidney by long-term lithium treatment

Area of Science:

• Nephrology
• Pharmacology
• Toxicology

Background:

• Lithium is a widely used mood stabilizer.
• Long-term lithium therapy can lead to renal complications, including nephrogenic diabetes insipidus.
• The precise relationship between functional and structural renal changes induced by lithium requires further elucidation.

Purpose of the Study:

• To investigate the relationship between functional and structural renal changes during long-term lithium treatment and after its withdrawal in a rat model.
• To assess the impact of lithium on renal concentrating ability and identify associated histological alterations.

Main Methods:

• Rats were administered lithium chloride (LiCl) in their diet for up to 21 weeks.
• Renal function was assessed using polyuria measurements, dehydration tests, and vasopressin tests.
• Plasma creatinine and urea levels were monitored.
• Kidney tissues were examined using light microscopy to evaluate structural changes in the distal convoluted tubule and collecting duct.

Main Results:

• Lithium treatment induced significant polyuria and reduced renal concentrating ability.
• Plasma creatinine and urea levels remained unchanged.
• Light microscopy revealed focal changes in the distal tubule and collecting duct, including nuclear/cellular polymorphism and tubular dilatation/atrophy after prolonged treatment.
• Functional impairments (polyuria, reduced concentrating ability) normalized within 4-8 weeks after lithium withdrawal.
• Structural changes persisted after lithium withdrawal and did not correlate with the degree of functional impairment.

Conclusions:

• Lithium induces reversible nephrogenic diabetes insipidus in rats, characterized by polyuria and impaired concentrating ability.
• The observed light microscopic structural changes in the distal nephron do not directly explain the functional deficits.
• Structural alterations may be a consequence of the lithium-induced polyuric state rather than the primary cause of the reversible diabetes insipidus.