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 of
thioacetamide (6.6 mmol kg-1 body wt) to rats. Samples of liver were obtained at 0, 3, 12, 24, 48, 72 and 96 h after
thioacetamide administration. 2.
Inducible nitric oxide synthase (iNOS) activity was determined in purified liver homogenates and a sharp 6 fold increase (P < 0.001) 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 expression of iNOS, as detected by its
mRNA levels, were parallel to the NOS
enzyme activity. Hepatocyte NO synthesis showed a progressive increase at 24, 48 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, where initial NO release was ten fold higher than in hepatocytes, a progressive increase was detected from 48 h which reached two fold of initial at 72 h of intoxication (192%; P < 0.001). Hepatic
cyclic GMP concentration did not change significantly. However, mitochondrial
aconitase 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 candidates to mediate iNOS expression, translocation (activation) of PKC was assayed in hepatocytes, and a significant two fold increase (P < 0.001) between 48 and 96 h after
thioacetamide intoxication was observed. When peritoneal macrophages from control rats were incubated with serum from
thioacetamide-treated rats, a sharp increase in NO release was detected 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 activity and NO release play a role in the pathophysiological mechanisms that trigger post-necrotic hepatocellular regeneration following
thioacetamide administration.