title: Decreased abundance of collecting duct urea transporters UT-A1 and UT-A3 with ECF volume expansion.
abstract: Clinical disorders of extracellular fluid (ECF) volume regulation are often associated with changes in plasma urea concentration. To investigate possible renal causes, we measured the relative abundance of the urea transporters UT-A1, UT-A2, and UT-A3 in renal medulla of rats with aldosterone-induced NaCl retention. ECF volume-expanded rats received aldosterone by osmotic minipump plus a diet containing a high level of NaCl. Control rats received the same infusion of aldosterone plus a virtually NaCl-free diet, which prevented ECF volume expansion. Preliminary measurements demonstrated transient positive Na and water balance, decreased serum urea concentration, and increased urea clearance, but no change in creatinine clearance. Immunoblotting of homogenates from inner medulla showed a marked decrease in the abundance of the collecting duct urea transporters UT-A1 and UT-A3. There were no differences in the abundance of UT-A2, aquaporin (AQP)-2, AQP-3, or AQP-4 in ECF volume-expanded rats vs. controls. Time course experiments demonstrated that changes in UT-A1 abundance paralleled the fall in serum urea concentration after the switch from a low-NaCl to a high-NaCl diet, whereas the fall in UT-A3 abundance was delayed. Candesartan administration markedly decreased the abundance of UT-A1 and UT-A3 in the renal inner medulla, which is consistent with a role for the angiotensin II type 1 receptor in urea transport regulation. The results support the view that ECF-related changes in serum urea concentration are mediated, at least in part, through altered urea transporter abundance.
authors.affiliation: Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Xiao-Yan
authors.initials: XY
authors.lastname: Wang
authors.forename: Kathleen
authors.initials: K
authors.lastname: Beutler
authors.forename: Jakob
authors.initials: J
authors.lastname: Nielsen
authors.forename: Søren
authors.initials: S
authors.lastname: Nielsen
authors.forename: Mark A
authors.initials: MA
authors.lastname: Knepper
authors.forename: Shyama
authors.initials: S
authors.lastname: Masilamani
mesh_terms: D000450:Aldosterone / Q000494:pharmacology; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D020346:Aquaporins / Q000378:metabolism; D001562:Benzimidazoles / Q000494:pharmacology; D001713:Biphenyl Compounds; D002352:Carrier Proteins / Q000096:biosynthesis / Q000502:physiology*; D004032:Diet; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D015151:Immunoblotting; D007150:Immunohistochemistry; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000096:biosynthesis / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017673:Sodium Chloride, Dietary / Q000378:metabolism; D013777:Tetrazoles / Q000494:pharmacology; D014508:Urea / Q000378:metabolism*; D000096982:Urea Transporters
chemical_list: D000450:Aldosterone; D057911:Angiotensin Receptor Antagonists; D020346:Aquaporins; D001562:Benzimidazoles; D001713:Biphenyl Compounds; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D017673:Sodium Chloride, Dietary; D013777:Tetrazoles; D014508:Urea; D000096982:Urea Transporters; C081643:candesartan