Splenic volume unloading may obscure right atrial signaling during simulated microgravity
- Paper number
IAC-06-A1.4.02
- Author
Ms. Heather Edgell, University of Waterloo, Canada
- Coauthor
Dr. Susan Kaufman, University of Alberta, Canada
- Year
2006
- Abstract
Weightlessness results in an upward fluid shift due to the absence of gravity. Microgravity-induced atrial distension should increase urine output due to a fluid shift towards the heart, yet this has not been observed during spaceflight. The spleen is known to regulate plasma volume via extravasation, and is also known to regulate water and sodium balance via the splenorenal reflex. After exposure to simulated microgravity, we hypothesize discordant signalling from the spleen (splenorenal reflex) and the heart (atrial natriuretic peptide; ANP) due to volume unloading and loading, respectively. Male Long-Evans rats were anesthetized with sodium pentobarbital (55-65 mg/kg, i.p.) and thiobutabarbital sodium (80-140 mg/kg, s.c). The femoral vein was cannulated for saline infusion. The splenic circulation was isolated by ligating accessory vessels. The gastric vein and artery were cannulated and the tips advanced to the splenic junction for measurement of pressure. In order to remove neural influence to/from the spleen and therefore determine physical parameters, the splenic nerve was removed. A Transonic flow probe was placed on the splenic artery and pressure and flow were measured for 5 min baseline followed by 5 min 30o head-down tilt (HDT). Animals were returned to horizontal, and the flow probe was placed around the splenic vein. HDT was repeated as above. In a separate group of animals, the right atrium was cannulated via the right jugular vein for right atrial pressure (RAP) measurements. A blood sample (0.8mL) was taken from the right atrium and replaced with saline. Animals were re-stabilized then underwent HDT for 5 min while recording RAP. A second 0.8mL blood sample was taken at the end of HDT. Radioimmunoassay was done for ANP quantification. Splenic venous pressure decreased from 9.19 +/- 0.94 to 8.29 +/- 0.98 mmHg (n=6, P=0.002), splenic venous flow decreased from 1.39 +/- 0.17 to 1.14 +/- 0.18 mL/min (n=6, P=0.031), splenic arterial pressure decreased from 87.67 +/- 7.98 to 83.70 +/- 9.09 mmHg (n=6, P=0.031), and splenic arterial flow decreased from 1.66 +/- 0.29 to 1.49 +/- 0.33 mL/min (n=6, P=0.037). Right atrial pressure increased from 3.28 +/- 0.88 to 4.01 +/- 1.00 mmHg (n=9, P=0.011). No changes in plasma ANP were seen after only 5 min HDT. We found that HDT causes fluid unloading of the spleen and we conclude that there are possible discordant signals from the heart and spleen influencing water and sodium homeostasis. All statistics are paired t-test or Signed Rank test.
- Abstract document
- Manuscript document
IAC-06-A1.4.02.pdf (🔒 authorized access only).
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