Effects of infection with Diplococcus pneumoniae on synthesis of ribonucleic acids in rat liver.

Rats infected with virulent Diplococcus pneumoniae developed a significant increase in the rate of incorporation of labelled orotate into hepatic RNA when compared with pair-fed controls inoculated with heat-killed organisms. The finding was readily detected in rats raised on either a low-protein diet (6% casein) or a diet containing adequate amounts of protein (18% casein). The increase in hepatic RNA synthesis was observed by 12h and was maximal by 16-20h after inoculation with the D. pneumoniae. Most of the infection-related increase in RNA synthesis was associated with the bound ribosomal RNA fraction of the liver. A small but less significant increase was observed in the synthesis of free ribosomal RNA. The increased synthesis of RNA in the liver of infected rats resulted in a marked elevation of the liver RNA/DNA ratio, the major increase being observed in concentration of bound ribosomal RNA fraction. When followed sequentially, the infection-related increase in synthesis of hepatic RNA was preceded by a flux of amino acids into liver and was followed by elevated synthesis rates of serum globulin proteins. These findings suggest that the infectious process was able to regulate hepatic RNA synthesis by altering the rate of transcription of new RNA. This mechanism was stimulated even in rats that had been severely depleted of body protein and amino acids by feeding them on a low-protein diet. The infection-related stimulation of liver RNA and protein synthesis thus appeared to take place at the expense of other body proteins.