The effects of hindlimb unweighting on the capacitance of rat small mesenteric veins

S. L. Dunbar, D. E. Berkowitz, E. M. Brooks-Asplund, A. A. Shoukas

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


Microgravity 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.

Original languageEnglish (US)
Pages (from-to)2073-2077
Number of pages5
JournalJournal of applied physiology
Issue number5
StatePublished - 2000


  • Microgravity
  • Pressure-diameter relationships
  • Sympathetic nervous system

ASJC Scopus subject areas

  • General Medicine


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