Fig. 6.  Effects of nitric oxide and naloxone on remifentanil pretreatment of hepatocytes viability and apoptosis by hypoxia reoxygenation. (A ) Cells in remifentanil (10 ng · ml⁻¹) and l-arginine (L-arg) pretreatment reduced reoxygenation-induced cell killing, measured by WST-8 dye, whereas the effect was prevented by coadministration of N -ω-nitro-l-arginine methyl ester (L-NAME) with or without remifentanil. Pretreatment with naloxone (NLX) could not block the effect of remifentanil preconditioning (RPC) (*P < 0.05 vs . Control). (B  and C ) Hepatocytes apoptosis was assessed using in situ  Hoechst 33342 staining. Normal nuclei show faint delicate chromatin stain, with the nuclei at the early stage of apoptosis displaying an increased condensation and brightness. Percentage of cells apoptosis decreased significantly in remifentanil or l-arginine pretreated groups compared with the control group, whereas these effects were prevented by coadministration of L-NAME but not opioid antagonist (naloxone) before remifentanil preconditioning. Magnification: 200×. Scale bar = 200 μm (*P < 0.05 vs . Control).