Toxic liver injury. Inhibition by dimethylnitrosamine of incorporation of labelled amino acids into proteins of rat-liver preparations in vitro

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Abstract
Incorporation of [C14valine into proteins of rat liver slices in vitro was inhibited by pre-incubation of the slices with dimethylnitrosamine (0.1 m[image]). No inhibition of incorporation was observed with kidney slices. Incorporation of [C14adenine into ribonucleic acid of rat liver slices in vitro was also inhibited on pre-incubation with dimethylnitrosamine. The concentration of dimethylnitrosamine in rat liver slices rapidly approached that of the incubation medium. The smallest dose of dimethylnitrosamine necessary to produce definite necrosis of the liver in the rat was about 20 mg/kg body weight. Concentrations of dimethylnitrosamine in the livers of rats given this dose reached levels of the order of 0.1 m[image], calculated in terms of liver water. Incorporation in vitro of [C14leucine into proteins of microsome plus cell-sap preparations of rat liver was measured at 2 and 3 hr. after the animals had been given a hepatic-necrotizing dose of dimethylnitrosamine (50 mg/kg body weight) and compared with that in similar preparations from untreated rats. Incorporation was considerably less in the preparations from treated rats than in those from untreated controls and the decrease was also present when treated microsomes were combined with control cell sap. Amino acid activation as measured by the amino acid-dependent pyro-phosphate-adenosine triphosphate exchange was unimpaired in treated animals at 2-3 hr. after the necrotizing dose of dimethylnitrosamine. Oxidative phosphorylation and the induction of adenosine triphosphatase were unimpaired in liver mitochondria isolated from rats 2 and 3 hr. after administration of dimethylnitrosamine. Incorporation of [Cl4-leucine into microsome plus cell sap preparations from the same animals was greatly impaired. The addition of dimethylnitrosamine to isolated mitochondria respiring in vitro had no effect on the oxidation of several substrates in concentrations up to 10 m[image]. The results are discussed in relation to the mechanism of liver damage by dimethylnitrosamine. They are thought to support the idea of a toxic metabolite as the tissue-damaging agent and its possible identity is discussed. They are also thought consistent with the hypothesis that the intra-cellular structures which give rise to microsomes on homogenizing are particularly vulnerable to the damaging action of dimethylnitrosamine.