Document Detail

Mechanism for negative water balance during weightlessness: an hypothesis.
MedLine Citation:
PMID:  3944046     Owner:  NLM     Status:  MEDLINE    
The mechanism for the apparent decrease in body fluid volume in astronauts during spaceflight remains obscure. The widespread postulate that the hypohydration is the result of the Henry-Gauer reflex, a diuresis caused by inhibition of vasopressin secretion resulting from increased left and perhaps right atrial (central) venous pressure, has not been established with direct measurements on astronauts. An hypothesis is proposed to account for fluid-electrolyte shifts during weightlessness. A moderate but transient increase in central venous pressure occurs when orbit is entered that is insufficient to activate the Henry-Gauer reflex but sufficient to stimulate the release of atrial natriuretic peptides. Increased sodium excretion would facilitate some increased urinary water loss. The resulting relatively dilute plasma and interstitial fluids would cause fluid to shift into the cellular space, resulting in edema in the head and trunk and inhibition of thirst and drinking. Thus the negative water balance in astronauts would be caused by a gradual natriuresis and diuresis coupled with reduced fluid intake.
J E Greenleaf
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  60     ISSN:  8750-7587     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  1986 Jan 
Date Detail:
Created Date:  1986-03-06     Completed Date:  1986-03-06     Revised Date:  2013-09-26    
Medline Journal Info:
Nlm Unique ID:  8502536     Medline TA:  J Appl Physiol (1985)     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  60-2     Citation Subset:  IM; S    
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MeSH Terms
Body Water / metabolism*
Models, Biological*

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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