This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Which of the follwoing is TRUE about free water clearance? 
Select and explain. 
A. Regulated by ADH, B. Regulated by aldosterone, C. Increased by furosemide, D. None of the above
A: Regulated by ADH
Answer: A: Regulated by ADH 
Explanation: "Free water clearance" (CH2O) is the difference between the urine volume and the clearance of osmoles (COsm). The excretion or retention of electrolyte-free water by the kidney is modulated by circulating vasopressin (ADH). ADH acts on renal V2-type receptors in the thick ascending limb of Henle and principal cells of the collecting duct (CD), increasing cyclic adenosine monophosphate (AMP) and activating protein kinase A (PKA)-dependent phosphorylation of multiple transpo proteins. Ref: Mount D.B. (2012). Chapter 45. Fluid and Electrolyte Disturbances. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.