Seasonal changes in thermoregulatory and hormonal changes in young and elder subjects

In Japan, there are four seasons, where environmental temperature changes very widely. With annual climate changes, body temperature regulation as well as hormonal regulation may be changed. The purpose of this study is to investigate the seasonal changes in temperature and hormonal regulation in elder subjects (69 ± 4.6 yrs; mean ± SD) and young subjects (21 ± 1.3 yrs; mean ± SD). The experiments were performed in the climatic chamber set at 26°C and 50% RH during spring, summer, autumn and winter. Each subject immersed his lower legs in hot water at 40 °C for 30 min in a sitting position. Core (tympanic) temperature, skin temperature and forearm sweat rates were recorded continuously. Blood was taken in pre‐immersion and in post‐immersion to measure the concentrations of antidiuretic hormone, plasma renin activity, angiotensin II, aldosterone, TSH, fT3 and fT4. The results obtained in spring and summer experiments showed that the rise of core body temperature and sweat rate during hot water immersion was lower in elder group than in young group. We will discuss the entire profile of the seasonal changes in thermoregulatory and hormonal function in young and elder subjects when the experiments in autumn and winter are completed.