Effects of the rat renotropic system on 14C-uridine incorporation into RNA and RNA precursors.

We used the incorporation of ¹⁴C-uridine into RNA of incubating kidney fragments from normal control rats to evaluate RNA metabolism. Sera from unilaterally nephrectomized rats (uni) obtained 20 hrs post-operatively stimulate ¹⁴C-uridine incorporation into RNA significantly more than sera from sham-operated rats (sham). Differently, sera from uni and sham rats have little influence on specific activities of endogenous uridine nucleotide pool in renal fragments. Renal extracts were obtained by homogenizing kidneys in saline. Extracts from kidneys of uni and sham rats 20 hrs post operation depress incorporation markedly, and each depresses to a similar extent, but kidney extracts dilute the specific activities of uridine pools. Correcting for the latter dilution demonstrates that kidney extracts alone have little effect on ¹⁴C-uridine incorporation into RNA. We then followed the results when these sera and extracts were combined. Compared to fragments incubating in sham sera and sham extracts, substitution of uni extracts or both uni extracts and uni sera enhances ¹⁴C-uridine into renal RNA, whether or not results are corrected for changes in the specific activities of the uridine pools. We conclude that after uninephrectomy there is a concurrent elevation in circulating renotropin and a tissue activating factor in the remaining kidney. The tissue factor can only form an excitor to ¹⁴C-uridine incorporation into RNA when serum is present. The rat renotropic system that enhances incorporation of ³H-thymidine into DNA also can stimulate ¹⁴C-uridine incorporation into renal RNA.