Determination of metabolic and heart rate responses of rats to treadmill exercise

Abstract

A rapid-flow, open-circuit, indirect calorimeter was developed and used to study metabolic rates of rats at rest and in response to three running speeds (14.3, 28.7, and 43.1 m/min) and five grades (1, 5, 10, 15, and 20%). Electrocardiogram connections were available within the apparatus for simultaneous determination of heart rate (f(H)). Validity of the calorimeter was established by observing responses to the addition of mixed gases including 14CO2, and by comparing oxygen consumptions when anesthetized rats were placed in the open- or a closed-circuit system. Half-response time of the system was 27 ± 3 s (mean ± SE). With one rat in each system values for O2 consumption (VO2) were 15.86 ± 0.91 and 15.77 ± 0.90 ml/kg per min for the open and closed systems, respectively. Highest VO2 values observed were 80.86 ± 2.48 ml/kg per min for rats running at 43.1 m/min on a 20% grade. The corresponding heart rates were 595 ± 5 beats/min. Correlation between VO2 and running speed ranged from 0.83 on 1% and 15% grades, to 0.90 on a 10% grade. Correlations between f(H) and speed ranged from 0.70 on a 1% grade, to 0.79 on a 10% grade. Steady-rate values for VO2 were 51.1 and 45.3 ml/kg per min during running at 14.3 m/min on 1% grade, and 69.0 and 65.1 ml/kg per min during running at 28.7 m/min on 15% grade.