Microgravity
and the Plasma Volume SPACEFLIGHT 52: 235, 2010.
Have you ever wondered why astronauts have so much
difficulty standing after return from a space mission? In addition to weakness from
loss of skeletal muscle there is a loss of plasma volume which constitutes
about one-third of the extracellular fluid volume. For example there was a reduction of the
plasma volume by about 10% after a 9 day mission (SLS-1). (1)
In addition with space flight there is invariably a
reduction in the thirst mechanism and water balance becomes negative within the
first 2 days of flight (1) Since water is an anti-oxidant because of the
hydrogen ions it contains, this invariable dehydration portends space-flight
oxidative stress, with in turn vulnerability to significant injuries to the
lining of the blood vessels (endothelium). I have addressed these issues with
numerous papers. (www.femsinspace.com)
It is indeed remarkable that rats subjected to swimming,
while attached to a weight, for only 4 hours (2) and rats subjected to space flight
after just 12 days (3) show identical pathology in the heart muscle. In both
cases there are projections extending from the capillaries. These projections
have been shown to be associated with gaps in the walls of the capillaries- conducive
to reductions of plasma volume. (4)
This reduction of plasma volume ( resistant to increased
water intake ) represents a serious complication of microgravity because invariably it triggers reductions of 2
vessel dilators and clot busters : atrial natriuretic peptide (A.N.P) and in turn nitric oxide. (N.O.) There is no solution to this life-threatening
vascular complication other than the combination of magnesium therapy necessary
for the synthesis and release of ANP and N.O and also gene therapy. (5, 6)
Pharmaceuticals can’t be used because ultimately, in the presence of
microgravity, they can not be sufficiently metabolized or excreted.
But why is A.N.P invariably
reduced, as for example, by as much as 40% after just 12 days in space? (1) Because
the upper chambers of the heart can sense the reduced plasma volume and
automatically reduce the release of A.N.P; otherwise all those subjected to
microgravity would die soon after lift-off.
The heart prevents this but at a great price.
William J.
Rowe M.D. FBIS
(
www.femsinspace.com)
References
- Leach Huntoon CS, Grigoriev
AL, Natochin YV. Fluid and
electrolyte regulation in spaceflight. Science and Technology Series 94. Am
Astronaut. Society, San Diego, 1998.
- 2. Kondalenko
VF, Sergeev YP. Changes in the
capillary ultrastructure of the rat myocardium following nonrepetitive
physical exertion. Byulleten Eksperimental
noi Biologii
I Meditsiny 78 : 88-91, 1974.
3. Philpott DE, Popova IA, Kato K, et al. Morphological and biochemical examination of
Cosmos 1887 rat heart tissue : Part 1-ultrastructure.
FASEB J. 4: 73-78, 1990.
4. Mc Donald DM, Thurston G,
Baluk P. Endothelial gaps as sites for
plasma leakage in inflammation. Microcirculation 6: 7-22, 1999.
5. Rowe WJ. Extraordinary hypertension after a lunar mission. Am J. Med 122; e1, 2009.
6.Rowe WJ. Potential renovascular hypertension, space missions, and the role of
magnesium. Intern J Nephrol and renovascular Dis. 2
: 51-57, 2009.