The effects of dietary cholesterol on metabolism and daily torpor patterns in Siberian hamsters.

The concentrations of fatty acids in the diet influence torpor in numerous species of mammals. Much less is known, however, about the potential effects of other types of dietary lipids. One study demonstrated that increasing dietary cholesterol levels during fall feeding increased torpor bout length and also decreased minimum body temperatures during hibernation by chipmunks. Another hibernation study with ground squirrels revealed that the cholesterol contents of both the cerebral cortex and the microsomes were significantly greater during arousal episodes than during torpor bouts, suggesting that cholesterol plays a role in preserving brain function during torpor. We thus predicted that dietary cholesterol enhances daily torpor in mammals as well. We also predicted that the level of cholesterol found in mammalian brain tissues during daily torpor increases with that of the diet. These hypotheses were tested in a series of laboratory feeding and daily torpor experiments involving Siberian hamsters (Phodopus sungorus) maintained on semisynthetic diets varying only in cholesterol content. Hamsters that were maintained on diets with cholesterol contents of 0.3%-2.5% during the summer entered winter daily torpor spontaneously, whereas those that were fed diets that contained no cholesterol did not. This is the first study to demonstrate the effects of a cholesterol-free diet on mammalian torpor. The presence of cholesterol in the summer diet also increased the level of cholesterol found in the brains of hamsters during the winter daily torpor period, but it did not during the summer. These findings support our hypotheses that dietary cholesterol is permissive for daily torpor in mammals and that it also increases brain cholesterol levels during the winter.