Tolvaptan is a vasopressin receptor antagonist. Vasopressin (a.k.a. ADH or antidiuretic hormone) helps to regulate water retention by absorbing water in the collecting ducts of the nephron.

The posterior pituitary gland, which extends from axonal projections originating from the hypothalamus, secretes both oxytocin and anti-diuretic hormone (ADH) or vasopressin 2. The hypothalamic ...