Mechanism of thirst attenuation during head-out water immersion in men.
The purpose was to determine whether extracellular volume or osmolality was the major contributing factor for reduction of thirst in air and head-out water immersion in hypohydrated subjects. Eight males (19-25 yr) were subjected to thermoneutral immersion and thermoneutral air under two hydration conditions without further drinking: euhydration in water (Eu-H2O) and euhydration in air, and hypohydration in water (Hypo-H2O) and hypohydration in air (3.7% wt loss after exercise in heat). The increased thirst sensation with Hypo-H2O decreased (P < 0.05) within 10 min of immersion and continued thereafter. Mean plasma osmolality (288 +/- 1 mosmol/kgH2O) and sodium (140 +/- 1 meq/l) remained elevated, and plasma volume increased by 4.2 +/- 1.0% (P < 0.05) throughout Hypo-H2O. A sustained increase (P < 0.05) in stroke volume accompanied the prompt and sustained decrease in plasma renin activity and sustained increase (P < 0.05) in plasma atrial natriuretic peptide during Eu-H2O and Hypo-H2O. Plasma vasopressin decreased from 5.3 +/- 0.7 to 2.9 +/- 0.5 pg/ml (P < 0.05) during Hypo-H2O but was unchanged in Eu-H2O. These findings suggest a sustained stimulation of the atrial baroreceptors and reduction of a dipsogenic stimulus without major alterations of extracellular osmolality in Hypo-H2O. Thus it appears that vascular volume-induced stimuli of cardiopulmonary baroreceptors play a more important role than extracellular osmolality in reducing thirst sensations during immersion in hypohydrated subjects.
Wada
F
F
Department of Physiology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Japan.
Sagawa
S
S
Miki
K
K
Nagaya
K
K
Nakamitsu
S
S
Shiraki
K
K
Greenleaf
J E
JE
D000328:Adult; D000388:Air; D009320:Atrial Natriuretic Factor / Q000097:blood; D001834:Body Water / Q000502:physiology; D002490:Central Nervous System / Q000502:physiology; D003681:Dehydration / Q000503:physiopathology; D005110:Extracellular Space / Q000502:physiology; D006257:Head; D006801:Humans; D007101:Immersion / Q000503:physiopathology*; D008297:Male; D009994:Osmolar Concentration; D010953:Plasma Volume / Q000502:physiology; D011311:Pressoreceptors / Q000502:physiology; D012083:Renin / Q000097:blood; D012677:Sensation / Q000502:physiology; D013318:Stroke Volume / Q000502:physiology; D013894:Thirst / Q000502:physiology*; D014667:Vasopressins / Q000097:blood; D014867:Water
D014867:Water; D014667:Vasopressins; D009320:Atrial Natriuretic Factor; D012083:Renin