Regulation of body fluid compartments during short-term
spaceflight.
Leach, Carolyn S., Clarence P. Alfrey, Wadi N. Suki, Joel I. Leonard,
Paul C. Rambaut, L. Daniel Inners, Scott M. Smith, Helen W. Lane,
Jane M. Krauhs.
Biomedical Operations and Research Branch, Medical Sciences
Division, National Aeronautics and Space Administration Johnson Space
Center, Houston, Texas 77058; Baylor College of Medicine, Houston,
Texas 77030; Uniformed Services University of the Health Sciences,
Bethesda, Maryland; North Atlantic Treaty Organization; KRUG Life
Sciences, Inc., Houston, Texas 77058
APStracts 2:0522A, 1995.
The fluid and electrolyte regulation experiment with seven subjects
was designed to describe body fluid, renal, and fluid regulatory
hormone responses during the Spacelab Life Sciences missions 1 (9
days) and 2 (14 days) . Total body water did not change significantly
during or after flight. Plasma volume (PV) decreased from (mean +/-
SD) 3.52 +/- 0.33 L before flight to 2.94 +/- 0.45 L 21 hours after
launch (P < 0.05), and extracellular fluid volume (ECFV)
decreased from 16.68 +/- 2.47 L before flight to 15.02 +/- 2.87 L 21
hours after launch (P < 0.10). Both remained below preflight
levels until after landing. Fluid intake decreased during
weightlessness and glomerular filtration rate (GFR) increased from
145.2 +/- 34.0 ml/min before flight to 170.3 +/- 47.7 ml/min in the
first 2 days of flight (P < 0.05) and 173.6 +/- 46.4 ml/min on
day 8 (P < 0.05). Urinary antidiuretic hormone (ADH) excretion
increased from 43.0 +/- 35.2 ng/24 h before flight to 182.5 +/- 179.0
ng/24 h on flight day 1 (P < 0.05), and urinary fluid excretion
decreased from 2561 +/- 1473 ml/24 h before flight to 1519 +/- 859
ml/24 h on flight day 1 (P < 0.10) and 1872 +/- 741 ml/24 h on
flight days 2 and 3 (P < 0.05). Plasma renin activity (PRA)
decreased from 1.50 +/- 0.90 before flight to 0.72 ng/ml/h in the
first few hours after launch (P < 0.10), and aldosterone
decreased from 114 +/- 90 pg/ml before flight to 58 +/- 68 pg/ml (P
< 0.05). PRA increased to 3.30 +/- 1.87 ng/ml/h a week later (P
< 0.05). During flight, plasma atrial natriuretic peptide
concentrations were consistently lower than preflight means, and
urinary cortisol excretion was usually greater than preflight levels.
Acceleration and other stresses probably caused the increases in ADH
and cortisol excretion, and a shift of fluid from the extracellular
to the intracellular compartment would account for reductions in
ECFV. Increased permeability of capillary membranes may be the most
important mechanism causing spaceflight-induced plasma volume
reduction, which is probably maintained by increased GFR and other
mechanisms. If the Gauer-Henry reflex operates during spaceflight, it
must be completed within the first 21 hours of flight and be
succeeded by establishment of a reduced plasma volume setpoint.
Received 30 December 1994; accepted in final form 17 November
1995.
APS Manuscript Number A1317-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95