Effects of hindlimb suspension and elevated ambient CO2 on rat growth and renal function

Background: Previous studies show that an ambient CO2 concentration of 2.0% may complicate interpretation of animal experiments conducted in spaceflig ht, while 0.7% CO2 exposure produces minimal effects. Hypothesis: With addi tional spaceflight factors, such as microgravity, effects from the 0.7% CO2 exposure may be amplified. Methods: To investigate the combined effects fr om microgravity and elevated CO2 on growth and renal function, two groups o f rats were hindlimb suspended for 37 d, and a third group served as an amb ulatory vivarium control (AMB). One suspension group was exposed to 0.7% CO 2 for 30 d (HLS + 0.7% CO2), while the other group (HLS) served as a suspen ded control. Both the AMB and HLS groups breathed room air at 0.03% CO2. Re sults: The HLS group showed responses consistent with past hindlimb suspens ion studies when compared with AMB, indicating similar reductions in organ and tissue weights and body weight gain. When comparing HLS + 0.7% CO2 anim als to HLS controls, exposure to CO2 revealed lowered food consumption and increased urine volume, NH3 and CO2 excretion, with no differences in any o f the other measured parameters, such as body weight gain, pH values, or el ectrolyte handling. Conclusion: This study shows that chronic exposure to b oth 0.7% ambient CO2 and hindlimb suspension together have little additiona l effect on rat growth and renal function.