Ribonucleic acid synthesis in the renal cortex at the initiation of compensatory growth

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Abstract
The mechanisms responsible for the increase in RNA per cell during the 1st 48 h of renal compensatory growth were studied in the renal cortex. Unilaterally nephrectomized, sham-operated or non-operated rats were used. Incorporation into RNA of labeled precursors was studied in vivo and in vitro. Sham-operation produced significant changes in precursor incorporation, absolute amounts of UTP and RNA, and the rate of RNA synthesis. At 6 h after surgery, the amount of RNA decreased in sham-operated controls, whereas that in growing cortex remained unchanged. Incorporation into RNA in vivo was greater in the growing cortex, although the rate of RNA synthesis was not increased. At 24 h, precursor incorporation into RNA and UTP and RNA synthesis were all increased in the growing cortex. Slices of growing cortex incorporated less labeled precursor into RNA than did cortex slices from sham-operated controls, from 3-48 h. Maximal differences were found from 6-24 h. An attempt was made to equalize endogenous precursor pool sizes by increasing the concentration of unlabeled uridine in the media; incorporation differences were narrowed significantly. Serum from nephrectomized animals did not increase precursor incorporation into RNA in vitro. An increase in RNA synthesis is an important factor in RNA accretion in the renal cortex beyond 12 h of compensatory growth. This is accompanied by increased UTP content and preceded by expansion of other pools. The amount of labeled precursor incorporated into RNA is greatly influenced by its delivery rate to the growing kidney in vivo and by intracellular dilution of expanded precursor pools in vitro.