Liver RNA polymerase activity in genetically obese and lean rats fed cholesterol

Abstract

Hepatic nuclear RNA polymerase activity (C 14-ATP incorporated into RNA) as well as microsomal protein synthesis (C 14-leucine incorporated into protein) was studied in vitro in groups of genetically obese female rats of the Zucker strain before and after the introduction of a diet containing cholesterol. A similar study was carried out in normal lean rats of the same strain. The obese homozygotes were found to demonstrate a higher level of protein synthesis as well as nuclear RNA polymerase activity than did the lean homozygotes. Following the feeding of the hypercholesteremic diet for either 7 or 28 days, protein synthesis and RNA polymerase activity were shown to be lower in both groups of females. However, these changes in protein synthesis induced by this diet were relatively greater among the obese rats, whereas the concomitant changes in polymerase activity were of the same order of magnitude between genotypes. These findings have been discussed in terms of the suggested “allosteric” nature of the RNA polymerase. Furthermore, the possibility of more than one specific RNA polymerase existing in the rat liver has been speculated to explain certain of the above differences.