title: Moderate sodium restriction does not alter lower body negative pressure tolerance.
abstract: OBJECTIVE
  Space travel with exposure to microgravity leads to a significant reduction in orthostatic tolerance on return to Earth, for which countermeasures are only partially successful. The purpose of this study was to examine the effect of moderate dietary sodium restriction on tolerance to LBNP.
  
  
  METHODS
  Eight healthy men, age 25.1+/-1.3 yr, volunteered for the study. Subjects were exposed to presyncopal LBNP after consuming their "typical" diet (C) for 5 d and after consuming a sodium restricted (SR) diet for 5 d. Diet sequence was randomized and adherence was verified by 24-h urine collection on the 4th and 5th days of each diet.
  
  
  RESULTS
  All subjects reached presyncope during the LBNP, regardless of diet. Urinary sodium excretion was 3390+/-950 mg on the C diet and 1174+/-560 mg on the SR diet. Urinary potassium was not different between the diets. Cumulative stress index scores were 655+/-460 (mm Hg x min) on the C diet and 639+/-388 (mm Hg x min) during SR. Cardiac volumes, BP and total peripheral resistance were not different at any stage of the LBNP between the diets, nor were catecholamines. Plasma renin activity, determined by radioimmunoassay, was significantly higher during SR at rest, and during all stages of LBNP in comparison with the control diet.
  
  
  CONCLUSIONS
  Moderate dietary sodium restriction is not detrimental to orthostatic tolerance.
authors.affiliation: Department of Physiology, Colorado State University, Fort Collins, CO 80523, USA.
authors.forename: L R
authors.initials: LR
authors.lastname: Davrath
authors.forename: R W
authors.initials: RW
authors.lastname: Gotshall
authors.forename: A
authors.initials: A
authors.lastname: Tucker
authors.forename: W Z
authors.initials: WZ
authors.lastname: Sadeh
authors.forename: G J
authors.initials: GJ
authors.lastname: Luckasen
authors.forename: T R
authors.initials: TR
authors.lastname: Downes
authors.forename: C C
authors.initials: CC
authors.lastname: Coonts
mesh_terms: D000328:Adult; D000337:Aerospace Medicine; D001794:Blood Pressure / Q000502:physiology; D002306:Cardiac Volume / Q000502:physiology; D004039:Diet, Sodium-Restricted; D006400:Hematocrit; D006801:Humans; D007024:Hypotension, Orthostatic / Q000188:drug therapy* / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology; D008150:Lower Body Negative Pressure / Q000009:adverse effects*; D008297:Male; D010807:Physical Endurance / Q000502:physiology*; D011188:Potassium / Q000652:urine; D012083:Renin / Q000097:blood; D012964:Sodium / Q000652:urine; D014655:Vascular Resistance / Q000502:physiology; D014893:Weightlessness / Q000009:adverse effects
chemical_list: D012964:Sodium; D012083:Renin; D011188:Potassium