Effects of infection and endotoxin on rat hepatic RNA production and distribution

Rat liver was quantitatively subfractionated into free ribosomal, bound ribosomal, nuclear, and soluble fractions to determine the effects of infection and endotoxin treatment on hepatic RNA production and distribution. A 4-h pulse label of [14C]orotic acid was used to monitor newly transcribed RNA; distribution was determined by measuring RNA content at various times after infection or endotoxin treatment. A significant increase in the rate of RNA synthesis was seen by 12 h and continued through 20 h in response to Streptococcus pneumoniae infection. During the peak hours of the RNA response, redistribution of RNA into the bound ribosomal fraction takes place at the expense of the free ribosomes. However, in Salmonella typhimurium and its endotoxin, more involvement of the free ribosoma fraction during the early stages of the infection was apparent. These data suggest that the hepatic RNA response takes place in two stages, an early "endotoxin" response, resulting in redistribution of cytoplasmic RNA into free ribosomes, and a later "infection" response, involving the mobilization of the bound ribosomes.