Effects of estrus cycle on thermoregulatory responses during exercise in rats

Summary In female rats, rectal temperature (T_re), tail vasomotor response, oxygen uptake, and carbon dioxide production were measured in proestrus and estrus stages during treadmill running at two different speeds at an ambient temperature (T_a) of 24° C. Experiments were performed at 2.00–6.00 a.m., when the difference inT_re was greatest between the two stages;T_re at rest in the estrus stage was 0.54° C higher than in the proestrus stage. In a mild warm environment, thresholdT_re for a rise in tail skin temperature (T_tail) was also higher in the estrus stage than in the proestrus stage. In contrast, no difference was seen in the thresholdT_re and steady stateT_re at the end of exercise between proestrus and estrus stages. These values were higher at the higher work intensity. was also similar between the two stages, except in the second 5 min after the beginning of exercise, when was greater andT_re rose more steeply in the proestrus stage. These data indicate that deep body temperature during exercise is regulated at a certain level depending on the work intensity and is not influenced by the estrus cycle.This study was supported in part by a Grant-in Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (Grant No. 62480114)