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Hypothesis Regarding Potential Injury of the Endothelium of the Normal Heart Complicating Prolonged Space Missions.

William J. Rowe, M.D.

The Russian experimental animal studies have demonstrated, with prolonged space flights, cardiac muscle injuries with impaired microcirculation, and high cardiac concentrations of catecholamines.  Elevations of the latter and significant losses of body magnesium, have been shown with manned orbital space flights.  Both of these alterations could be aggravated by the necessity of unremitting endurance exercise with magnesium ion deficiency partly due to the removal of free magnesium ions from the circulation by chelation with catecholamine-induced free fatty acids.  There is the potential for 4 vicious cycles:  1).  The inverse relationship between high catecholamines and low magnesium ions.  2).  Coronary vasospasm induced by both of the latter with the potential for injury to the endothelium and reduction in endothelium-derived relaxing factors (nitric oxide).  3).  Reduction in myocardial oxygen supply secondary to coronary vasospasm and local and systemic thrombogensis and with increased oxygen demand with the potential for severe ischemia conducive to further catecholamine release.  4).  Magnesium ion deficiency enhancing angiotensin 2 action, resulting in increased aldosterone and in turn increased magnesium excretion.  Both magnesium deficiency and high catecholamines may injure the heart through increased free radical formation, which in turn, may aggrevate radiation-induced injuries by similar mechanisms.  Finally the demonstration of diminished plasma cGMP (during weightlessness), which could be a result of endothelial injuries, supports this hypothesis.   William J. Rowe M.D.  Former assistant clinical prof. of medicine Medical College Of Ohio At Toledo. 

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