This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Disorders of pituitary gland, Subject name: Medicine
Tolvaptan is used in? 
Select and explain. 
A. Hyponatremia, B. Hypernatremia, C. Nephrogenic diabetes insipidus, D. Decreased water clearance
A: Hyponatremia
Answer: A: Hyponatremia 
Explanation: Selective vasopressin V2 -receptor antagonist: is indicated for Hypervolemic and euvolemic hyponatremia (i.e., serum sodium level < 125 mEq/L) or less marked hyponatremia that is symptomatic and has resisted correction with fluid restriction. It is used for hyponatremia associated with congestive hea failure, liver cirrhosis, and SIADH secretion. Initiate or re-initiate in hospital environment only. Selective Vasopressin V2-receptor antagonist: causes an increase in urine water excretion results in an increase in free water clearance (aquaresis), a decrease in urine Osmolality, and an increase in serum sodium concentration