Tolvaptan is used in autosomal dominant polycystic kidney disease (ADPKD) to slow cyst growth. Its mechanism of action in ADPKD beyond simple aquaresis is:

• A Tolvaptan directly inhibits mTORC1 in cyst epithelial cells similar to sirolimus, but via a V2 receptor-dependent pathway
• B Aquaresis with reduced urine osmolality reduces hydrostatic pressure in the renal collecting system, mechanically limiting cyst distension
• C V2 receptor blockade upregulates AQP2 channels in cyst membranes, allowing osmotic reabsorption of cyst fluid back into tubular lumen
• D V2 receptor antagonism reduces intracellular cAMP in tubular/cyst epithelial cells, blocking cAMP-dependent mTOR and CFTR-mediated chloride secretion that drives cyst fluid accumulation ✓

Explanation

In ADPKD, cyst growth is driven by abnormal cAMP signaling in tubular epithelial cells. Vasopressin (ADH) acts on V2 receptors in collecting duct cells to raise cAMP via Gs/adenylyl cyclase. Elevated cAMP in ADPKD cells (which also have defective PC1/PC2 polycystin channels) stimulates mTOR-mediated proliferation and activates CFTR chloride channels, causing transepithelial chloride (and water) secretion into the cyst lumen, expanding cysts. Tolvaptan (V2 receptor antagonist) blocks this cAMP elevation, simultaneously reducing tubular water reabsorption (aquaresis) and suppressing cAMP-driven cyst growth. TEMPO 3:4 trial demonstrated 49% reduction in cyst growth rate.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.