The maximum thermogenic capacity of brown fat cells from control and cold 
acclimated rats was measured using a continuous-flow microcalorimetric system. 
The content of the 32.000 D, brown fat specific protein, thermogenin, was 
measured in the cells used for heat production measurements by competitive 
ELISA. The ratio between the maximal thermogenic capacity and the amount of 
thermogenin for control and cold acclimated rats was compared. It was found that 
the ratio between the two parameters decreased during cold acclimation due to a 
decrease in maximal thermogenic capacity and an increase in the amount of 
thermogenin, indicating regulation of heat production either at thermogenin or 
receptor level.