title: Arginine vasopressin-dependent and AVP-independent mechanisms of renal fluid absorption during thirsting despite glucocorticoid-mediated vasopressin suppression.
abstract: OBJECTIVE
  Glucocorticoids seem to modify the release and effects of plasma arginine vasopressin (pAVP). However, underlying processes are not well understood. This study aimed to evaluate the mechanism of the modulating effects of glucocorticoids on pAVP and renal water reabsorption.
  
  
  METHODS
  Fluid deprivation tests were performed without (d0) and after one (d1) and five days (d5) of oral prednisolone (Pred) pretreatment in a dosage relevant to drug therapy (30 mg/day).
  
  
  METHODS
  Twelve healthy male volunteers participated in this trial.
  
  
  METHODS
  Plasma and urinary osmolality, pAVP, renin, aldosterone, plasma atrial natriuretic peptide (ANP) as well as urinary secretion of aquaporin-2 (AQP2) and prostaglandin E(2) (PGE2) were analysed.
  
  
  RESULTS
  An appropriate rise in pAVP was observable during thirsting (P < 0.001), which was absent after Pred pretreatment. However, the plasma and urinary osmolality after Pred treatment did not differ when compared with the basal thirsting test. Unchanged urinary AQP2 excretion suggests AVP-independent mechanisms of renal fluid reabsorption. Plasma renin concentration as well as ANP was substantially increased after Pred intake at d1 and d5 (both P < 0.05), which may mediate such AVP-independent mechanisms. Urinary PGE2 secretion was not influenced by Pred pretreatment, making a PGE2-mediated effect on renal AQP2 translocation and water permeability unlikely. Increased efficacy of exogenous desmopressin at d1 and d5 indicates also a relative increase in AVP sensitivity of the tubular cells after Pred intake.
  
  
  CONCLUSIONS
  The here presented data are compatible with an increased AVP sensitivity and a partially AVP-independent regulation of AQP2 translocation and renal fluid reabsorption during glucocorticoid treatment.
authors.affiliation: Medical Clinic of Endocrinology, Diabetes and Nutrition, Charite - Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: Friederike
authors.initials: F
authors.lastname: Ufer
authors.forename: Sven
authors.initials: S
authors.lastname: Diederich
authors.forename: Erling B
authors.initials: EB
authors.lastname: Pedersen
authors.forename: Joachim
authors.initials: J
authors.lastname: Spranger
authors.forename: Andreas F H
authors.initials: AF
authors.lastname: Pfeiffer
authors.forename: Volker
authors.initials: V
authors.lastname: Bähr
authors.forename: Knut
authors.initials: K
authors.lastname: Mai
mesh_terms: D000042:Absorption / Q000187:drug effects; D000328:Adult; D001127:Arginine Vasopressin / Q000097:blood*; D003894:Deamino Arginine Vasopressin / Q000494:pharmacology; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D009994:Osmolar Concentration; D013894:Thirst / Q000187:drug effects*
chemical_list: D005938:Glucocorticoids; D001127:Arginine Vasopressin; D003894:Deamino Arginine Vasopressin