Effect of photoperiod and acclimation temperature on nonshivering thermogenesis and GDP-binding of brown fat mitochondria in the Djungarian hamster Phodopus s. sungorus.

Acclimation to short photoperiod at 23 degrees C constant Ta caused P. sungorus to improve their NST capacity from 752 to 1,082 mW. Chronic cold exposure in short photoperiod further enhanced the NST capacity, reaching a maximum level of 1,573 mW at -5 degrees C acclimation temperature. Improvements in NST capacity were always accompanied by an increase in brown fat mitochondrial mass and GDP-binding of brown fat mitochondria, in proportion with the cold load applied during temperature acclimation (23 degrees, 15 degrees, 5 degrees, -5 degrees C). Brown fat mitochondrial protein increased from 7.41 mg (23 degrees C Ta, long photoperiod) through 21.6 mg (23 degrees C Ta, short photoperiod) and 81.6 mg (-5 degrees C Ta, short photoperiod). This approximately 10-fold increase was accompanied by a approximately 35-fold increase in GDP-binding (2.0, 7.3 and 71.6 nmol GDP bound, respectively), demonstrating that the increase in capacity for uncoupled respiration in brown fat is of primary significance for thermogenic acclimation to cold as well as to short photoperiod.