Protection of hepatotoxic and lethal effects of CCl4 by partial hepatectomy

CCl4 is a hepatotoxic haloalkane, capable of producing hepatocellular fatty degeneration and centrilobular necrosis. Previous reports indicate induction of liver regeneration after 36-48 hr of CCl4 treatment, which is considered as a secondary effect. The present investigation was undertaken to evaluate the primary effects of CCl4 on hepatic DNA synthesis and to correlate liver regeneration with CCl4 toxicity. These studies were conducted in normal and actively regenerating livers using male Sprague-Dawley rats undergoing sham operation (SH), or partial (70%) hepatectomy (PH). Incorporation of 3H-thymidine (3H-T) in hepatocellular nuclear DNA and autoradiographic analyses of liver sections served as indices for hepatocellular regeneration. Initial experiments established that peak regeneration occurs at 2 days post-PH (PH2) and liver regeneration phases out by 7 days post-PH (PH7). SH and PH rats were challenged with a single ip dose of either corn oil vehicle or CCl4 at either 0.1 ml/kg (to represent subtoxic dose) or 2.5 ml/kg (to represent toxic dose). The low dose of CCl4 was not toxic and did not alter 3H-T incorporation and percentage labelled cells at 6 or 24 hours after administration to SH, PH2 or PH7 groups, indicating that there was no interference with PH-stimulated hepatocellular regeneration. The high dose of CCl4 was significantly hepatotoxic and lethal in SH rats, while in PH2 rats both hepatotoxic and lethal effects were significantly decreased. 3H-T incorporation as well as percentage labelled cells, highly stimulated by PH, were significantly decreased by high dose of CCl4. However, hepatocellular regeneration in PH2 rats treated with high dose of CCl4 was still significantly higher than SH or PH7 groups by virtue of the stronger stimulatory effect of PH. In PH7 rats, where hepatocellular regeneration had returned to the SH level, the hepatotoxic and lethal effects of the large dose of CCl4 were also restored. These findings show that the progressive phase of a single high dose of CCl4 injury which normally culminates in hepatotoxic and lethal effects is significantly mitigated by previously stimulated hepatocellular regeneration. High dose of CCl4 suppresses hepatocellular regeneration at early time points after administration in contrast to the smaller subtoxic dose of CCl4. By virtue of the much stronger stimulatory effect, PH results in the protection against the hepatotoxic and lethal effects of CCl4 despite the obtunding effects of the high dose on hepatocellular regeneration.