COMPARISON BETWEEN SEASONAL AND THERMAL ACCLIMATION IN WHITE RATS: II. SURFACE TEMPERATURE, VASCULARIZATION, AND IN VITRO RESPIRATION OF THE SKIN

Abstract

The effect of cold temperature on the skin was studied on white rats exposed to two different types of environmental conditions. Two groups of adult rats kept in individual cages were continuously exposed for 3 months to constant cold temperature (18° and 6 °C) in the laboratory (indoor rats) while other groups of the same colony kept in groups of 10 were exposed for the same length of time to the fluctuating environmental conditions prevailing outside (outdoor rats).Indoor rats acclimated to 18 °C and 6 °C showed the same increase in the number of opened capillaries in the ears over the number observed in controls acclimated to 30 °C. "Summer and winter" outdoor rats showed the same number of capillaries as the "18 °C or 6 °C" indoor rats. Signs of injury healing such as thicker epidermis and larger nuclei were found in the ears of all the "6 °C" rats but in none of the "winter" rats. While the skin temperature measured at + 6 °C was slightly higher (0.4 to 1.0 °C) in rats acclimated at 6 °C than in those at 30 °C, it was lower (1.3 to 2.9 °C) in "winter" than in "summer" rats. After 28 days of acclimation, the rate of oxygen uptake of the dorsal skin of the foot was lower in "6 °C" than in "30 °C" rats but after 84 days it was significantly higher in the cold-acclimated rats. Similarly, after 3 months, the respiratory rate of the dorsal skin of the foot was higher in "winter" rats than in "summer" rats.