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The effects of hindlimb unweighting on the capacitance of rat small mesenteric veinsMicrogravity is associated with an impaired cardiac output response to orthostatic stress. Mesenteric veins are critical in modulating cardiac filling through venoconstriction. The purpose of this study was to determine the effects of simulated microgravity on the capacitance of rat mesenteric small veins. We constructed pressure-diameter relationships from vessels of 21-day hindlimb-unweighted (HLU) rats and control rats by changing the internal pressure and measuring the external diameter. Pressure-diameter relationships were obtained both before and after stimulation with norepinephrine (NE). The pressure-diameter curves of HLU vessels were shifted to larger diameters than control vessels. NE (10(-4) M) constricted veins from control animals such that the pressure-diameter relationship was significantly shifted downward (i.e., to smaller diameters at equal pressure). NE had no effect on vessels from HLU animals. These results indicate that, after HLU, unstressed vascular volume may be increased and can no longer decrease in response to sympathetic stimulation. This may partially underlie the mechanism leading to the exaggerated fall in cardiac output and stroke volume seen in astronauts during an orthostatic stress after exposure to microgravity.
Document ID
20040112696
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Dunbar, S. L.
(The Johns Hopkins University School of Medicine Baltimore, Maryland 21205, United States)
Berkowitz, D. E.
Brooks-Asplund, E. M.
Shoukas, A. A.
Date Acquired
August 21, 2013
Publication Date
November 1, 2000
Publication Information
Publication: Journal of applied physiology (Bethesda, Md. : 1985)
Volume: 89
Issue: 5
ISSN: 8750-7587
Subject Category
Aerospace Medicine
Distribution Limits
Public
Copyright
Other
Keywords
Non-NASA Center
NASA Discipline Cardiopulmonary

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