Influence of norepinephrine and fasting on the oxygen consumption of genetically-obese mice.

Oxygen consumption was monitored in fed and fasted, lean and obese mice of the ob/ob strain before and after subcutaneous injections of norepinephrine (NE). The increase in oxygen consumption after NE was of a similar magnitude in both lean and obese fed mice, but of a longer duration in the obese. Prior fasting caused a diminution of the response in the lean but was associated with an enhanced response in the obese mice. Fasting also resulted in a significant depression of the resting oxygen consumption of the obese mice but not of the lean. The relevance of these findings to the inability of the obese mouse to withstand cold exposure and to the maintenance of the obese state is discussed.