title: Intrarenal urea recycling leads to a higher rate of renal excretion of potassium: an hypothesis with clinical implications.
abstract: OBJECTIVE
  This review aims to illustrate why urea recycling may play an important role in potassium (K⁺) excretion and to emphasize its potential clinical implications.
  
  
  RESULTS
  A quantitative analysis of the process of intrarenal urea recycling reveals that the amount of urea delivered to the distal convoluted tubule is about two-fold larger than the quantity of urea excreted in the urine. As the number of osmoles delivered to the late cortical distal nephron (CCD) determines its flow rate when aquaporin 2 water channels have been inserted in the luminal membrane of principal cells, urea recycling may play an important role in regulating the rate of excretion of K⁺ when the distal delivery of electrolytes is not very high.
  
  
  CONCLUSIONS
  Urea recycling aids the excretion of K⁺; this is especially important in patients with disorders or those who are taking drugs that lead to a less lumen-negative voltage in the CCD. As a large quantity of urea is reabsorbed daily in the inner medullary collecting duct, the assumption made in the calculation of the transtubular K concentration gradient that there is no appreciable reabsorption of osmoles downstream CCD is not valid.
authors.affiliation: Keenan Research Centre in the Li Ka Shing Knowledge Institute, St. Michael's Hospital, Division of Nephrology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Kamel S
authors.initials: KS
authors.lastname: Kamel
authors.forename: Mitchell L
authors.initials: ML
authors.lastname: Halperin
mesh_terms: D000818:Animals; D006706:Homeostasis; D006801:Humans; D006947:Hyperkalemia / Q000378:metabolism / Q000503:physiopathology; D007668:Kidney / Q000378:metabolism* / Q000503:physiopathology; D011188:Potassium / Q000378:metabolism*; D014508:Urea / Q000378:metabolism*; D014882:Water-Electrolyte Balance
chemical_list: D014508:Urea; D011188:Potassium