Induction of tyrosine aminotransaminase and ornithine decarboxylase in isolated perfused regenerating rat liver

Effect of azathioprine and carbon tetrachloride on induction of hyperplastic liver nodule and hepatocellular carcinoma by diethylnitrosamine and N-2-fluorenylacetamide in rats

The enhancing or inhibitory action of the hepatotoxic agents, carbon tetrachloride (CCl4) and azathioprine (AZP), on the evolution of hyperplastic liver nodule (HN) and hepatocellular carcinoma (HCC) in diethylnitrosamine (DEN)- and N-2-fluorenylacetamide (FAA)-treated rats (control group) was tested. The area of gamma-glutamyl transpeptidase(gamma-GTP)-positive HN and/or foci in the eighth week was remarkably small in rats fed on a diet containing FAA and AZP (the AZP group), but was quite large in rats fed a diet containing FAA in addition to repeated CCl4 injections (the CCl4 group). HCC was first detected in the 21st week and the incidence of HCC within the 36 weeks of the experiment was very high in the CCl4 group. However, no tumor, including HCC, was detected in the AZP group during this observation period. No essential differences in the biochemical characteristics of HCC between the control group and the CCl4 group were observed with respect to several enzyme activities. The increased activity of liver aniline hydroxylase observed 12 hr after the administration of FAA, AZP, or DEN decreased when AZP was administered simultaneously with FAA to rats treated with DEN in advance. The mechanisms of the enhancing of inhibitory effect observed are discussed with special reference to the drug-drug interactions.

Hormonal control of ornithine decarboxylase in isolated liver cells and the effect of ethanol oxidation

The regulation of ornithine decarboxylase activity was studied in freshly isolated rat hepatocytes incubated in a chemically defined medium for 5 h. Glucagon, dibutyryl cyclic AMP, insulin and dexamethasone produced dramatic increases in ornithine decarboxylase activity, 6--100-times the basal activity. Actinomycin D inhibited completely the stimulatory action of these substances. With glucagon, dibutyryl cyclic AMP and insulin, the rise in ornithine decarboxylase activity was rapid but transient, peaking at 200 min and then declining rapidly. By contrast, the response to dexamethasone was gradual and sustained in the 5 h incubation. The transient nature of the response to glucagon was unaltered by repeated additions of optimally effective doses of glucagon suggesting the development of 'refractoriness' to the actions of this hormone. Ethanol oxidation inhibited by 50% the stimulation of ornithine decarboxylase by glucagon and dexamethasone and this effect was blocked by 4-methylpyrazole, an inhibitor of alcohol dehydrogenase. Acetate (2.5--20 mM), the metabolic product of hepatic ethanol oxidation, was also effective. The data indicate that glucagon, insulin and glucocorticoids are all effective in stimulating the activity of ornithine decarboxylase in isolated hepatocytes but they differ in their duration and time of peak of action. Additionally, the inhibitory effect of ethanol on the hormonal stimulation of ornithine decarboxylase is dependent on its oxidation and may be mediated by acetate.