Tissue-specific changes in RNA synthesis in vivo during anoxia in crucian carp

The overall energy budget for protein synthesis (i.e., transcription plus t ranslation) is thought to consist of fixed and variable components, with RN A synthesis accounting for the former and protein synthesis the latter. Dur ing anoxia, the downregulation of protein synthesis (i.e., the variable com ponent), to reduce energetic demand, is an important aspect of survival in crucian carp. The present study examines RNA synthesis during anoxia by lab eling with [H-3]uridine. A novel synthesis rate calculation is presented, w hich allows for the tissue-specific salvage of uridine, with synthesis rate s finally expressed relative to DNA. After 48 h anoxia, the decline (29%) i n brain RNA synthesis and increases in the heart and liver (132 and 871%, r espectively) support known RNA functions during hypoxic/anoxic survival. Th is study provides evidence that, in an anoxia-tolerant species, survival me chanisms involving RNA are able to operate because tissue-specific restruct uring of the RNA synthesis process enables fixed synthesis costs to be main tained; this may be as vital to survival as exploiting the variable energet ic demand of protein synthesis.