Tolvaptan as a tool in renal physiology

Area of Science:

• Nephrology
• Endocrinology
• Molecular Physiology

Background:

• The Brattleboro rat model, lacking circulating vasopressin, has been crucial for studying kidney physiology.
• Assessing V2 receptor-mediated vasopressin actions typically involves dDAVP infusion in Brattleboro rats.
• Cessation of Brattleboro rat supply necessitates alternative models for vasopressin V2 receptor research.

Purpose of the Study:

• To establish and validate a novel in vivo model for assessing vasopressin V2 receptor-mediated actions in the rat kidney.
• To investigate the efficacy of tolvaptan, a V2 receptor antagonist, in mimicking conditions related to vasopressin signaling.

Main Methods:

• Utilized osmotic minipumps for continuous in vivo infusion of tolvaptan in rats.
• Measured urinary osmolality to assess kidney concentrating ability.
• Quantified renal expression of aquaporin-2 (AQP2), aquaporin-3 (AQP3), and epithelial sodium channel subunits (β-ENaC, γ-ENaC).

Main Results:

• Tolvaptan infusion significantly reduced urinary osmolality (<300 mosmol/kgH₂O) compared to controls (>2,000 mosmol/kgH₂O).
• Tolvaptan treatment markedly decreased renal abundance of AQP2, AQP3, β-ENaC, and γ-ENaC.
• In vitro studies confirmed tolvaptan's inhibition of vasopressin-induced AQP2 phosphorylation.

Conclusions:

• Tolvaptan infusion in rats provides a viable alternative model for studying V2 receptor-mediated vasopressin actions.
• This model effectively replicates key physiological and molecular responses observed in Brattleboro rats.
• Tolvaptan serves as a valuable tool for dissecting vasopressin signaling pathways in the kidney.