Document Detail

Renal, endocrine, and cardiovascular responses to bed rest in male subjects on a constant diet.
MedLine Citation:
PMID:  15068228     Owner:  NLM     Status:  MEDLINE    
BACKGROUND: Exposure to actual and simulated microgravity induces cardiovascular deconditioning through a variety of factors. Although the mechanisms involved remain uncertain, one involves alterations in volume-regulating systems--the hypothesis being tested in this study. To maximize our ability to detect subtle changes in the volume-regulating systems, subjects were studied on a high-average salt intake to maximally suppress these systems basally. METHODS: Fourteen healthy male subjects underwent 14-day head-down tilt bed rest (HDTB) during which a constant 200 mEq sodium, 100 mEq potassium diet was maintained. Daily 24-hour urine collection was performed; plasma renin activity, serum aldosterone, plethysmography, and cardiovascular system identification were performed during a control period (pre-HDTB) and at the end of HDTB (end HDTB). RESULTS: Sodium excretion increased initially (pre-HDTB = 182.8 +/- 10.4 mEq/total volume; early HDTB = 236.4 +/- 13.0; p = .002) and then returned to baseline values. Potassium excretion increased 4 days after the initiation of HDTB and remained elevated thereafter (pre-HDTB = 82.2 +/- 2.4/total volume; mid- to late HDTB = 89.4 +/- 2.1; p = .02). Plasma renin activity increased significantly with HDTB (pre-HDTB = 1.28 +/- 0.21 ng/mL/h; end HDTB = 1.69 +/- 0.18; p = .01), but serum aldosterone did not change. A significant decrease in autonomic responsiveness and an increase in leg compliance were observed. CONCLUSIONS: We conclude that even in the presence of a high-average salt intake diet, simulated microgravity leads to renal, cardioendocrine, and cardiovascular system alterations that likely contribute to cardiovascular deconditioning.
S Marlene Grenon; Natalie Sheynberg; Shelley Hurwitz; Grace Xiao; Craig D Ramsdell; Michael D Ehrman; C Lan Mai; Siri Rostoft Kristjansson; Grete H Sundby; Richard J Cohen; Gordon H Williams
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S.; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Journal of investigative medicine : the official publication of the American Federation for Clinical Research     Volume:  52     ISSN:  1081-5589     ISO Abbreviation:  J. Investig. Med.     Publication Date:  2004 Mar 
Date Detail:
Created Date:  2004-04-07     Completed Date:  2004-04-20     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  9501229     Medline TA:  J Investig Med     Country:  Canada    
Other Details:
Languages:  eng     Pagination:  117-28     Citation Subset:  IM; S    
Division of Endocrinology, Brigham and Women's Hospital, Boston, MA 02115, USA.
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MeSH Terms
Bed Rest
Cardiovascular Deconditioning / physiology*
Endocrine System / physiology*
Head-Down Tilt / physiology
Immobilization / physiology*
Kidney / physiology*
Leg / blood supply
Potassium / urine
Renin-Angiotensin System / physiology
Sodium / urine
Sodium Chloride, Dietary
Veins / physiology
Weightlessness / adverse effects*
Grant Support
Reg. No./Substance:
0/Sodium Chloride, Dietary; 7440-09-7/Potassium; 7440-23-5/Sodium
R J Cohen / MA Inst Technol, Cambridge, MA; G H Williams / Brigham & Women's Hosp, Boston, MA

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