title: Role of osmolality and plasma volume during rehydration in humans.
abstract: To determine how the sodium content of ingested fluids affects drinking and the restoration of the body fluid compartments after dehydration, we studied six subjects during 4 h of recovery from 90-110 min of a heat [36 degrees C, less than 30% relative humidity (rh)] and exercise (40% maximal aerobic power) exposure, which caused body weight to decrease by 2.3%. During the 1st h, subjects rested seated without any fluids in a thermoneutral environment (28 degrees C, less than 30% rh) to allow the body fluid compartments to stabilize. Over the next 3 h, subjects rehydrated ad libitum using tap water and capsules containing either placebo (H2O-R) or 0.45 g NaCl (Na-R) per 100 ml water. During the 3-h rehydration period, subjects restored 68% of the lost water during H2O-R, whereas they restored 82% during Na-R (P less than 0.05). Urine volume was greater in H2O-R than in Na-R; thus only 51% of the lost water was retained during H2O-R, whereas 71% was retained during Na-R (P less than 0.05). Plasma osmolality was elevated throughout the rehydration period in Na-R, whereas it returned to the control level by 30 min in H2O-R (P less than 0.05). Changes in free water clearance followed changes in plasma osmolality. The restoration of plasma volume during Na-R was 174% of that lost. During H2O-R it was 78%, which seemed to be sufficient to diminish volume-dependent dipsogenic stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: John B. Pierce Foundation Laboratory, New Haven, Connecticut.
authors.forename: H
authors.initials: H
authors.lastname: Nose
authors.forename: G W
authors.initials: GW
authors.lastname: Mack
authors.forename: X R
authors.initials: XR
authors.lastname: Shi
authors.forename: E R
authors.initials: ER
authors.lastname: Nadel
mesh_terms: D000328:Adult; D000465:Algorithms; D001810:Blood Volume; D001835:Body Weight; D003681:Dehydration / Q000503:physiopathology*; D004573:Electrolytes / Q000032:analysis; D006358:Hot Temperature; D006801:Humans; D008297:Male; D009994:Osmolar Concentration; D005082:Physical Exertion; D012964:Sodium / Q000008:administration & dosage* / Q000032:analysis; D013894:Thirst; D014556:Urine; D014867:Water
chemical_list: D004573:Electrolytes; D014867:Water; D012964:Sodium