Responses of the pituitary-adrenal system of mice to an environment of high temperature and humidity

Changes in plasma glucose and corticosterone levels under an environment of high temperature and humidity similar to summers in Japan were investigated. When mice were exposed to high temperature (30-40° C) and humidity (70%), the plasma glucose levels increased with a short-term exposure and decreased with a long-term exposure compared to that of the control mice housed at room temperature (23° C) and humidity (55%). The magnitude of increase of plasma corticosterone levels depended on the degree of ambient temperature and the duration of exposure to the stressful conditions. The plasma corticosterone concentration was highest at 2 hr after initiation of the temperature stress and was reduced at 4 and 6 hr after the treatment: The plasma corticosterone had returned to the control level at 8 hr after the exposure. The dexamethasone treatment inhibited the increase of plasma corticosterone in stress-mice. These results suggest that the response of the plasma corticosterone is a better index than that of glucose for estimation of stress-degree.