Rat growth, body composition, and renal function during 30 days increased ambient CO2 exposure

Background: In experiments using rodents onboard orbiting spacecraft, speci mens may be exposed to an increase in ambient CO2. Hypothesis: Many of the physiological changes reported in rats (and humans) for spaceflight are sim ilar to those observed with increased CO2, raising the question whether the observed changes are due to spaceflight or more specifically, the elevated ambient CO2. Methods: To evaluate the effects of increased CO2, at levels similar to those experienced during spaceflight, three groups of adult male rats (n = 10) were exposed to ambient CO2 concentrations of 0.3, 0.7 and 2 .0% for 30 d. Control rats were exposed to atmospheric conditions (0.03% CO 2) for each group. Results: There were alterations in water turnover, food intake, and renal function with increased CO2. Blood pH, total CO2, and pla sma concentrations of Na+, Ca2+, and corticosterone were significantly elev ated at the 2.0% exposure, while plasma PO43- was reduced. At the 0.3% and 0.7% CO2 exposures, many of these changes were not significant. Animals exp osed to 0.3% CO2 showed a significant increase in total body Na+. Urinary C a2+, K+, creatinine, corticosterone, and total CO2 excretion were higher at 2.0%, but only Ca2+ and CO2 excretion were significantly elevated at 0.7%, and there was no significant alteration in renal function at 0.3%. Conclus ion: Chronic increased ambient CO2 levels, similar to those observed on the Space Shuttle and proposed for the International Space Station, elicit com pensatory responses in rats which may affect interpretation of experiments designed to evaluate the effects of exposure to microgravity.