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Effects of hindlimb suspension and elevated ambient CO2 on rat growth and renal function
1Life Sciences Division, NASA Ames Research Center, Moffett Field, CA 94035, USA.
Background:
Previous studies show that an ambient CO2 concentration of 2.0% may complicate interpretation of animal experiments conducted in spaceflight, while 0.7% CO2 exposure produces minimal effects.
Hypothesis:
With additional spaceflight factors, such as microgravity, effects from the 0.7% CO2 exposure may be amplified.
Methods:
To investigate the combined effects from microgravity and elevated CO2 on growth and renal function, two groups of rats were hindlimb suspended for 37 d, and a third group served as an ambulatory vivarium control (AMB). One suspension group was exposed to 0.7% CO2 for 30 d (HLS + 0.7% CO2), while the other group (HLS) served as a suspended control. Both the AMB and HLS groups breathed room air at 0.03% CO2.
Results:
The HLS group showed responses consistent with past hindlimb suspension studies when compared with AMB, indicating similar reductions in organ and tissue weights and body weight gain. When comparing HLS + 0.7% CO2 animals to HLS controls, exposure to CO2 revealed lowered food consumption and increased urine volume, NH3 and CO2 excretion, with no differences in any of the other measured parameters, such as body weight gain, pH values, or electrolyte handling.
Conclusion:
This study shows that chronic exposure to both 0.7% ambient CO2 and hindlimb suspension together have little additional effect on rat growth and renal function.