[Features of thermogenesis in newborn rats].

The millicalorimetry technique with simultaneous recording of the EMG and of the rectal and brown fat tissue temperatures revealed the energy contributions of motor activity and of brown fat to total heat production in newborn rats of 3-4 and 8-9-day age. In absence of motor activity no increase of heat production occurs. In 3-4-day old rats, the heat production per unit of motor activity in greater than in 8-9-day old rats. Nevertheless, as the result of more intense movements, the 8-9-day old rats handle better a moderate cold stress: their rectal temperature proved higher by 1.3 degrees than in the 3-4-day old rats.