Temperature regulation during treadmill exercise in the rat

Abstract

The response of colonic and tail-skin temperatures to treadmill exercise was assessed in female Sprague-Dawley rats using incremental and single-stage exercise protocols to investigate the relationship between deep body temperature and work rate. O2 uptake (.ovrhdot.VO2) was measured by flow-through technique to evaluate the exercise intensity. Experiments were performed in ambient temperatures below (22.degree.-25.degree. C) and above (33.degree.-35.degree. C) the thermoneutral zone of the rat. During graded incremental exercise there was a linear relationship between colonic temperature (Tco) and .ovrhdot.VO2 in both the cooler and warmer ambient temperatures. Tco and tail-skin temperature (Tsk) at comparable work rates in the cooler and warmer environments were 40.22 .+-. 0.59, 34.84 .+-. 1.10.degree. C and 42.04 .+-. 0.57, 38.39 .+-. 1.54.degree. C, indicating that the rise in Tco was unrelated to the severity of exercise. During single-stage exercise the rats were able to achieve thermal equilibrium but only at low work rates and in the cool environment (22.degree.-25.degree. C). There were no significant differences in Tco at the 1st 3 levels of single-stage exercise (stage 1, 39.63 .+-. 0.34.degree. C; stage 2, 39.67 .+-. 0.49.degree. C; stage 3, 39.75 .+-. 0.50.degree. C) despite significant differences in .ovrhdot.VO2 (stage 1, 4.3 .+-. 0.7 ml .cntdot. min-1 .cntdot. 100 g-1; stage 2, 5.3 .+-. 0.6 ml .cntdot. min .cntdot. 100 g-1; stage 3, 7.6 .+-. 1.2 ml .cntdot. min-1 .cntdot. 100 g-1). This demonstrates that there was no relationship between the level of Tco maintained during exercise and the work intensity. Temperature regulation appears to be poorly regulated in rats during treadmill exercise at high work rates and/or in a warm environment. This is probably caused by the rats inability to augment heat dissipation by utilizing saliva spreading as a thermolytic mechanism while exericising on a treadmill.