Heat stress induces a three-phase thermoregulatory response in different hot and humid environments in rats.

As global warming intensifies, heat waves occur more frequently around the world. Heat stress from hot and humid environments poses a significant threat to human health. It can cause a significant increase in core body temperature (CBT), and even lead to life-threatening heat stroke. Extremely high CBT is considered the most important clinical symptom and prognostic indicator of heat stroke. To study it, we implanted temperature-monitoring capsules into the abdominal cavities of rats to measure their CBT values. The rats were then exposed to different hot and humid environments to monitor the resultant changes in their CBTs. The results showed that heat stress could induce a three-phase thermoregulatory response in rats under different conditions. A temperature plateau was observed as part of the three-phase thermoregulatory response, at a similar CBT across different conditions. The duration of this plateau can reflect the thermotolerance of rats in hot and humid environments. The third stage of the three-phase thermoregulatory response reflects the pathogenesis of heat stroke, which may present the key stage of heat injury. Moreover, a certain range of humidity did not affect the thermoregulatory responses of rats, but exerted a significant impact once a certain threshold was reached. In this study, the CBTs of the rats in different environments were monitored to characterize their thermoregulatory responses under heat stress. In particular, the discovery of the plateau phase and humidity threshold may help to better understand the effects of high temperature and humidity conditions on living organisms.