Cytokines are thought to play an important role in the hepatocellular dysfunction that occurs during sepsis. Some cytokines have been shown to increase lipogenesis and to induce toxicity in isolated hepatocytes. Oxygen free radicals have been implicated as mediators of some cytokine effects. In this study we investigate a possible protection action of S-adenosyl-L-methionine against the toxic effects of cytokines on isolated hepatocytes. Isolated rat hepatocytes were precultured for 24 hr and then cultured for 1, 2, 3, 6, 12, or 24 hr in the presence or absence of S-adenosyl-L-methionine (12 micromol/l0) and/or either tumor necrosis factor (100, 200, or 500 ng/ml) or interleukin-1 (30, 60, or 120 IU/ml). Lactate dehydrogenase (media), and malondialdehyde, reduced glutathione, and the incorporation of D-[U- 14 C] glucose into different lipid fractions (cells) were determined. Both cytokines significantly increased hepatocyte malondialdehyde content, lactate dehydrogenase release, and triacylglycerol synthesis. None of these effects were observed in the presence of S-adenosyl--L-methionine. In addition, S-adenosyl-L-methionine was able to attenuate the decrease in phosphatidylcholine labeling also induced by both cytokines, and to prevent the increase in free fatty acid synthesis induced by tumor necrosis factor. Incubation in the presence of S-adenosyl-L-methionine also increased hepatocyte glutathione content (7.1 +/- 0.7, after 24 hr, vs 3.6 +/- 0.3 nmole/mg protein, P < 0.01), and prevented the decrease in glutathione induced by tumor necrosis factor (5.4 +/- 0.2 vs 2.1 +/- 0.1 nmole/mg protein, 100 ng/ml TNF alpha at 24 hr, P < 0.01). Our results show that S-adenosyl-L-methionine has a protective effect on hepatocytes against the in vitro effect of cytokines.