INVOLVEMENT OF NITRIC-OXIDE SYNTHESIS IN HEPATIC PERTURBATIONS INDUCED IN RATS BY A NECROGENIC DOSE OF THIOACETAMIDE

1 The biological actions of nitric oxide (NO), a highly diffusible and short-lived radical, range from signal transduction to cytotoxicity. The present study investigated whether NO is released in the course of liver necrosis and regeneration induced by a single necrogenic dose o f thioacetamide (6.6 mmol kg(-1) body wt) to rats. Samples of liver we re obtained at 0, 3, 12, 24, 48, 72 and 96 h after thioacetamide admin istration. 2 Inducible nitric oxide synthase (iNOS) activity was deter mined in purified liver homogenates and a sharp 6 fold increase (P<0.0 01) in iNOS activity was recorded at 48 h of intoxication, followed by a slight but progressive increase at 72 and 96 h. Changes in the expr ession of iNOS, as detected by its mRNA levels, were parallel to the N OS enyzme activity. Hepatocyte NO synthesis showed a progressive incre ase at 24, 38 and 72 h, to 8 (P<0.001), 13 (P<0.001) and 13 (P<0.001) times the initial values, respectively. 3 In isolated Kupffer cells, w here initial NO release was ten fold higher than in hepatocytes, a pro gressive increase was detected from 48 h which reached two fold of ini tial at 72 h of intoxication (192%, P<0.001). Hepatic cyclic GMP conce ntration did not change significantly. However, mitochondrial aconitas e activity decreased markedly at 12 and 24 h of intoxication showing a sharp increase towards normal values at 48 h which was maintained at 72 and 96 h. 4 As protein kinase C (PKC) is one of the likely candidat es to mediate iNOS expression, translocation (activation) of PKC was a ssayed in hepatocytes, and a significant two fold increase (P<0.001) b etween 48 and 96 h after thioacetamide intoxication was observed. When peritoneal macrophages from control rats were incubated with serum fr om thioacetamide-treated rats. a sharp increase in NO release was dete cted with serum obtained at 48 h. reaching at 96 h a value four fold ( P < 0.001) that of the control. 5 These results suggest that iNOS acti vity and NO release play a role in the pathophysiological mechanisms t hat trigger post-necrotic hepatocellular regeneration following thioac etamide administration.