To investigate the effects of arsenite on cell proliferation and the signal 
transduction in hapatocytes in vivo, rats received a single injection of sodium 
arsenite immediately after partial hepatectomy. Characteristic DNA fragmentation 
was observed at 4h after the arsenite-injection in partially hepatectomized 
liver, while it was not detected either in the control (partial hepatectomy 
only) or arsenite-injected normal (without partial hepatectomy) liver. The 
effect of the arsenite-injection on the activation of extracellular 
signal-regulated kinase (ERK) was not observed in the normal or the partially 
hepatectomized liver. The activity of p38 mitogen-activated protein kinase 
(MAPK) markedly increased after 15min to 2h after the arsenite-injection in 
partially hepatectomized liver while no or a less increase was observed in the 
arsenite-injected normal or the control, respectively. The Jun N-terminal kinase 
(JNK) was activated to a maximal level, about six-fold the maximum of the 
control, at 15min after the injection with partial hepatectomy. The 
arsenite-injection markedly increased the phosphorylated forms of c-Jun and 
ATF-2 and the protein levels of c-Jun, p53 and p21(WAF1/CIP1) in the partially 
hepatectomized liver. These results suggested that arsenite induced apoptosis in 
the hepatocytes in vivo, through the enhancement of the activation of JNK and 
p38 MAPK caused by partial hepatectomy and the p53-dependent p21(WAF1/CIP1) 
protein expression.