title: Is the Gauer-Henry reflex important for immersion diuresis in men?
abstract: BACKGROUND
  This study examines the relationship between the threshold for plasma vasopressin concentration [PVP] responses and diuresis (Gauer-Henry reflex), and tests the hypothesis that water intake would not influence diuresis.
  
  
  METHODS
  Eight men (19-25 yr) underwent four treatments: euhydration in air (Eu-air), euhydration in water immersion (Eu-H2O), and with prior 3.6% hypohydration in air (Hypo-air), and hypohydration in immersion (Hypo-H2O). Ad libitum drinking was allowed during the 3-h experimental and 1-h recovery periods.
  
  
  RESULTS
  Drinking was greatest during the first 10 min: 3.5 ml x kg(-1) with Hypo-air (450 ml x 3 h(-1)) and only 1.7 ml x kg(-1) (p < 0.05) with Hypo-H2O (235 ml x 3 h(-1)). At 1 h, concomitant [PVP] decreased from a control level of 6.6+/-1.5 to 4.0+/-1 .0 pg x ml(-1) (delta = 2.6 pg x ml(-1), p < 0.05) with Hypo-air, and from 5.9+/-0.6 to 2.3+/-0.2 pg x ml(-1) (delta = 3.6 pg x ml(-1), p < 0.05) with Hypo-H2O. Urine flow was unchanged from control level (<1.0 ml x min(-1)) with Hypo-air, Hypo-H2O, and Eu-air, but increased to 4-5 ml x min(-1) with Eu-H2O. Neither water intake volume nor urine flow was related to the magnitude of [PVP] depression. Regression of Uosm/Posm ratio on [PVP] and urine flow indicated that [PVP] above 2 pg x ml(-1) did not affect urine flow. Thus, ad libitum water intake in previously hypohydrated subjects did not affect urine flow or the decrease in [PVP]. The threshold [PVP] to initiate significant diuresis was about 2 pg x ml(-1), and significant diuresis can occur with no change in [PVP] maintained at about 1 pg x ml(-1) during immersion in euhydrated subjects.
  
  
  CONCLUSIONS
  Thus, it appears that the Gauer-Henry reflex is not the major mechanism for immersion-induced diuresis. Clearly, other diuretic factors are also involved.
authors.affiliation: Laboratory for Human Environmental Physiology, NASA, Ames Research Center, Moffett Field, CA 94035-1000, USA. jgreenleaf@mail.arc.nasa.gov
authors.forename: J E
authors.initials: JE
authors.lastname: Greenleaf
authors.forename: K
authors.initials: K
authors.lastname: Shiraki
authors.forename: S
authors.initials: S
authors.lastname: Sagawa
authors.forename: K
authors.initials: K
authors.lastname: Miki
authors.forename: F
authors.initials: F
authors.lastname: Wada
authors.forename: K
authors.initials: K
authors.lastname: Nagaya
authors.forename: R
authors.initials: R
authors.lastname: Torii
authors.forename: L C
authors.initials: LC
authors.lastname: Keil
mesh_terms: D000328:Adult; D000388:Air; D003681:Dehydration / Q000503:physiopathology*; D004231:Diuresis / Q000502:physiology*; D004327:Drinking Behavior / Q000502:physiology*; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D007101:Immersion / Q000503:physiopathology*; D008297:Male; D009994:Osmolar Concentration; D012018:Reflex / Q000502:physiology*; D012044:Regression Analysis; D013997:Time Factors; D014563:Urodynamics / Q000502:physiology; D014667:Vasopressins / Q000097:blood* / Q000502:physiology*; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D014667:Vasopressins