Species-specific changes in the metabolic control of food intake: integrating the animal with its environment

Research on the metabolic control of feeding has been almost exclusively restricted to the study of laboratory rats. This poses no problem if all animals respond to metabolic challenges similarly; however, they do not. Unlike rats, Syrian, Turkish, and to a lesser degree, Siberian hamsters do not increase their food intake following food restriction. It has been argued that hamsters do not increase their food intake following a fast in laboratory tests because in their natural habitat they presumably would have a hoard of food in their burrows to buffer them from any shortfalls in the food supply above ground. An alternative hypothesis is proposed based on the self-imposed fast that occurs during a bout of hibernation in hamsters and the subsequent absence of compensation of food intake upon arousal. This fixed rate of feeding during the hibernation season may facilitate utilization of their food cache. Therefore, it may be that the failure to increase feeding following an experimenter-induced fast in the laboratory is due to the expression of this fixed pattern of feeding that normally accompanies hibernation. The relationship between food restriction and reproductive status is also discussed in terms of species- and gender-specific responses. Hamsters also differ from rats in that they do not increase their food intake following severe alterations in carbohydrate metabolism (via acute injections of 2-deoxy-D-glucose (2DG) or insulin), lipid metabolism (via administration of the fatty acid oxidation blocker methyl palmoxirate (MP), or from alterations in both (via combined administration of MP and 2DG). Perhaps food intake in hamsters is controlled by the waxing and waning of inhibitory rather than stimulatory factors.(ABSTRACT TRUNCATED AT 250 WORDS)