Depression of transcription and translation during daily torpor in the Djungarian hamster (Phodopus sungorus)

During daily torpor, Djungarian hamsters reduce their metabolic rate by more than 70% below their resting metabolic rate for several hours per day. We investigated whether this depression of metabolism is associated with a reduction in transcription and translation. Liver tissue was sampled in defined metabolic states: during normometabolism, in the torpid state and after arousal from torpor. Nuclei were isolated from liver tissue and subjected to nuclear run-on assays at an assay temperature of 25 degreesC. We observed a similar to40% decrease in transcriptional initiation in liver nuclei of hamsters which had attained minimal metabolic rate during torpor as compared to nuclei from normometabolic hamsters. During arousal from torpor, the transcriptional run-on activity recovered to the normometabolic level. Polysome profile analysis of liver tissue was used to determine the proportion of actively translating polysomes. Profiles of liver samples from torpid animals show a disaggregation of polysomes compared to profiles from normometabolic hamsters, which indicates that, in addition to transcription, protein synthesis decreases during torpor. These results indicate that during torpor a specific inhibition of the energetically costly processes of RNA and protein synthesis contributes to the overall metabolic depression.