Purine and pyrimidine nucleotide patterns of normal, differentiating, and regenerating liver and of hepatomas in rats.

Abstract

Abstract The pattern of purine and pyrimidine nucleotides was elucidated in freeze-clamped preparations of normal liver; in hepatomas of very slow (9618A), intermediate (8999), and rapid (3924A) growth rates; in regenerating liver; and in liver of neonatal rats. The ribonucleotide content was measured by high-pressure liquid chromatography, and that of the deoxyribonucleoside triphosphates was determined by enzymic assays. In the liver, the contents of deoxythymidine triphosphate, deoxycytidine triphosphate, deoxyadenosine triphosphate, and deoxyguanosine triphosphate were very low (1 to 5.1 nmol/g wet weight). The concentrations of deoxyribonucleoside triphosphates were increased relative to liver in all hepatomas, and the rise correlated with the tumor growth rates. Adenosine triphosphate (ATP) concentration and total adenine nucleotide amounts gave a negative correlation with tumor growth rate. The ATP level in hepatoma 3924A was decreased to 43% of the normal liver concentration. By contrast, contents of cytidine triphosphate and of total cytosine nucleotides were increased in all 3 liver tumors. The xanthosine monophosphate content of hepatoma 3924A was 233% of that of normal liver and guanosine monophosphate concentration in all three hepatomas was above the liver values. There were no other consistent changes in the guanine and uracil nucleotide concentrations in the hepatomas. In the 24-hr regenerating liver, the cytidine triphosphate and xanthosine monophosphate levels were higher than normal liver values. Unlike the liver tumors, the regenerating liver had increased uridine nucleotides and normal ATP concentration. In the liver of 6-day-old rats, with the exception of a 27% increase in cytidine triphosphate level, the ribonucleotide contents did not differ from those of adult rat liver. In normal rat liver, a period of ischemia of up to 10 min resulted in extensive dephosphorylation of ATP and other nucleoside triphosphates, with the degraded material accumulating as monophosphates and nucleosides. However, hepatoma 3924A (and the other hepatomas to a much lesser extent) possessed the ability to maintain ATP levels near normal values for 10 min of ischemia. This capability was lost following iodoacetate treatment, suggesting that the maintenance of a normal ATP level in hepatoma 3924A during ischemia was associated with the high activity of anaerobic glycolysis in this tumor. The results indicate that aspects of the pyrimidine and purine nucleotide pattern are linked with transformation or progression in hepatomas of different growth rates. The pattern of deoxynucleoside triphosphate pools in rapidly growing differentiating and regenerating liver and in hepatoma 3924A shows that the concentrations of these key precursors of DNA biosynthesis are particularly increased in the tumor, and this may confer selective advantages on the neoplastic cells.