Early Changes in Pyrimidine Biosynthesis after Partial Hepatectomy.

After partial hepatectomy, a series of morphological and biochemical changes occur in the residual liver that result in the reconstitution of the original tissue mass (I). Biochemical alterations occur in the areas of glycogen and lipid metabolism, free amino acid concentrations and protein biosynthesis, as well as in ribonucleic and deoxyribonucleic acid metabolism (1, 2). The biosynthesis of deoxyribonucleic acid after partial hepatectomy has been extensively studied in several laboratories (3-5). DNA biosynthesis, as reflected by radioautography, occurs at a very slow rate during the 16to l&hour period after operation, but rises rapidly to a peak at 20 to 24 hours, and then sharply declines (6). An increase in the mitotic rate may be noted about 6 to 8 hours after the rise in DNA biosynthesis (2, 7). In contrast, changes in RNA metabolism occur at an earlier stage after partial hepatectomy. Although a net increase in RNA is detectable by 20 hours (8, 9), an enhanced incorporation of labeled precursors into RNA may be observed as early as 6 hours after partial hepatectomy (10-12). This increased RNA biosynthesis may be found in the nucleolar, nuclear, and cytoplasmic fractions (10, 13, 14) whereas changes in microsomal RNA occur later (15). A more detailed study by Fujioka, Koga, and Lieberman (16) has shown an enhanced rate of incorporation of ‘4Corotate into all fractions of liver RNA occurring immediately after partial hepatectomy. These observat,ions are in accordance with the increase in liver RNA polymerase noted by Busch et al. (17) that take place 6 hours after partial hepatectomy. The purpose of the present report is to describe some changes in the biosynthesis of pyrimidines that occur almost immediately after partial hepatectomy.