Aims: 

Mice on fat-rich diet exposed to total fasting exhibit progressive daytime hypothermia from the third week onwards and after losing more than 60% of their original body mass by the fourth week regain their original obese body mass when re-fed. Similar studies on ob/ob mice have not been published so far.

Methods: 

Ob/ob mice lacking leptin and implanted with biotelemetric transmitter have been exposed to total fasting together with free availability of water and their body core temperature and locomotor activity were continuously monitored at thermoneutral ambient temperature. Body mass and food intake were monitored daily. Body temperature and locomotor activity responses were sought that would indicate the level and length of fasting still compatible for survival.

Results: 

As opposed to what was previously observed in mice with dietary obesity, ob/ob mice showed daily hypothermia down to 31–32°C from the second day of fasting onwards in the early morning hours. The next two to three weeks of fasting were characterized by a reduction of daily core temperature excursions and by a gradual fall of night activity, the latter having been very high during the first two weeks of fasting. Body mass fell well below 50% of the starting value by the end of fasting. Re-feeding led to slow increases of food intake and body mass.

Conclusion: 

Mice with genetic obesity well tolerate long-term total fasting just as mice with dietary obesity do. Still, the dynamics of changes in core tempearture and locomotor activity is different in the two groups of obese mice during fasting. Further studies are needed to learn the way cerebral energy supply is ensured in these two models of obesity during long-term fasting that may also shed light to the mechanisms of different energetic responses (i.e. changes of body core temperature and locomotor activity).

Support: 

OTKA T062598