Physiological responses of rhesus monkeys to exercise at varied temperatures

This research characterizes the effects of selected physiological stressors such as work and various environmental heat loads in rhesus monkeys. Non-human primates (N = 6) were behaviorally conditioned to exercise in a wheel ergometer at approximately 3 METs (1 MET = 3.5 ml O2 uptake.kg-1.min-1). On separate days, each monkey attempted six work/rest cycles (10 min work: 1 min rest) at 15, 25, and 35 degrees C (Tdb), vapor pressure < 10 mm Hg. Core temperature (Tco), body weight (BW) and blood samples were taken immediately before and after exercise. Excessively high heat storage rates dictated that the 35 degrees C trial be limited to three work/rest bouts. The change in Tco during exercise was significantly greater in the 35 degrees C trial than during the 15 and 25 degrees C work bouts. Sweat rate, as determined by the change in BW over time, was also significantly greater during the 35 degrees C trial as compared to the 15 and 25 degrees C trials. Glucose levels (mean +/- SE) declined significantly during exercise from 4.35 +/- 0.1 and 4.58 +/- 0.4 mmol to surprisingly low levels of 1.67 +/- 0.2 and 1.76 +/- 0.2 mmol in the 15 and 25 degrees C trials, respectively. Increases in blood lactate, glycerol, and triglycerides were observed independent of environmental temperature. Free fatty acids increased during exercise in the 15 and 25 degrees C trials but declined slightly during the shorter 35 degrees C trial. The findings of this study indicate that the increased heat storage observed at higher environmental heat loads appears to substantially limit the amount of work these primates can perform, possibly the result of a limited sweat production capacity. Additionally, plasma glucose following exercise decreased to levels not typically seen in humans. The general metabolic profile in these primates was otherwise similar to that observed in humans at this work level.