Ventilatory CO₂ response in endurance-trained rats

Summary

A CO₂ rebreathing technique was used to assess possible changes in the ventilatory response to CO₂ in rats following a 14-week swim training program. Over the final 9 weeks, the rats swam 1 h per day with a weight of 2.5% of the body weight attached to the tail. Ventilation was measured by a barometric method in awake, restrained rats in a total body plethysmograph at CO₂ concentrations of 0, 2, 4, 6, and 8%, with an initial O₂ concentration of approximately 100%. Ventilation increased in the trained rats with increasing CO₂ from 775 ml·min⁻¹·kg⁻¹ at 0% CO₂ to 1,387 ml·min⁻¹·kg⁻¹ at 8% CO₂. This increase was a consequence of a 34% increase in tidal volume and a 32% increase in breathing frequency. In comparison with a group of sedentary control rats, there was a significantly higher ventilation and tidal volume at 0% CO₂; however, this difference disappeared with increasing levels of CO₂. A significantly lower resting heart rate was observed in the exercised (296±44 beats·min⁻¹, mean±SD) compared to the sedentary control rats (380±42). It was concluded that, while the normal training response of resting bradycardia was observed following this duration and intensity of training, endurance swimming had no significant effect on the ventilatory response to CO₂ in the rat.