Cross adaption between stress and cold in rats.

Three-hour immobilization stress was imposed on male adult rats of Wistar strain by restraining them on a board 6 days a week for 1-8 weeks. The stressed rats showed less body weight gain during the experiment compared to the controls. These stressed animals manifested an improved cold tolerance as shown by no significant fall in colonic temperature in the cold at -5 degrees C for 300 min during the experimental period, while the colonic temperature of the controls fell progressively. Nonshivering thermogenesis as assessed by noradrenaline-induced increase in oxygen consumption was significantly potentiated in the stressed rats. The weight and protein content of the intercapsular brown adipose tissue (BAT) increased and BAT mitochondria were more packed in the stressed rats. Plasma insulin, insulin/glucagon molar ratio and thyroxine levels were lowered in the stressed rats, while the plasma triiodothyronine level remained unchanged. Removal of interscapular BAT led to a loss of improved cold tolerance and a significant reduction of nonshivering thermogenesis in the stressed rats. These results indicate that repetitive stress may induce cross adaptation between stress and cold through an enhanced capacity of nonshivering thermogenesis mediated, at least in part, via stimulation of BAT function.