Warm rearing modifies temperature regulation in rats.

The effects of early (postnatal), long-term warm exposure on thermoregulatory system of rats were compared with those resulting from warm acclimation induced in adult animals. To obtain warm-reared (wr) rats pregnant females 7 days before term were permanently exposed to a constant ambient temperature of 35 degrees C and their offsprings were housed under these conditions for at least 6 months. Wr rats differed from both control and warm acclimated (wa) animals morphologically as well as functionally. They were leaner and lighter but their tails and feet grew relatively bigger. Moreover, warm rearing led to a marked and highly significant elevation in mass of salivary gland (the main source of water for evaporative cooling). Core temperature in wr rats was regulated at a significantly higher level during the day and at night. Moreover, hyperthermia reduced the exercise performance less in wr than in wa rats. In conclusion, early exposure to high environmental temperature modifies the development of temperature regulation in a way different from that occurring during thermal acclimation in the adult. Changes occurring in wr rats might mimic genetical adaptations of a population to variety of thermal environments.