[Effects of nonthermal stresses on brown adipose tissue thermogenesis]

Abstract

Repetitive intermittent immobilization stress has been shown to induce an improved cold tolerance through an enhanced capacity of nonshivering thermogenesis (NST). In the present study, effects of immobilization (3 hrs daily for 4-5 weeks), exercise training (running with treadmill 30 min daily, 30 m/min under 8 degrees inclination for 4-5 weeks) and chronic corticosterone treatment (subcutaneous injection at a dose of 0.3 mg/100 g for 4-5 weeks) were investigated on in vitro and/or in vivo thermogenesis of rat interscapular brown adipose tissue (BAT). BAT thermogenesis in vitro was measured in the minced tissue blocks in Krebs-Ringer phosphate buffer using a Clark type oxygen electrode. DNA content per whole BAT pad was greater in the stressed rats, while it was not affected by exercise training and corticosterone. Noradrenaline-and glucagon-stimulated oxygen consumptions were significantly greater in the stressed rats, while significantly smaller in the trained rats as compared with respective controls. Corticosterone treatment failed to affect those values in terms with both per mg tissue and per whole tissue pad, except the less noradrenaline-stimulated oxygen consumption in terms with per mg tissue and DNA. In vivo thermogenesis was assessed by the changes of temperatures in colon (Tcol), BAT (TBAT) and tail skin (Tsk) induced by noradrenaline or glucagon infusion under anesthesia Noradrenaline and glucagon increased the TBAT and the extent of increase was greater in the stressed rats. These results indicated: 1. Repetitive immobilization stress induces the tissue hyperplasia and enhances thermogenic activity of BAT. 2. Exercise training suppresses BAT thermogenesis. 3. Chronic corticosterone administration does not affect BAT thermogenesis. It may be concluded that the enhancing or suppressing effect of nonthermal stress on BAT thermogenesis is due to other factor(s) than corticosterone.