Reduction of carbon tetrachloride toxicity by prior administration of a single small dose in mice and rats.

Mice were given progressively smaller doses of carbon tetrachloride (CCl4) and at intervals later the LD50 of a second dose was determined. The LD50 was greater than in previously untreated mice as soon as 10 min after the first dose, increased to a maximum between 12 and 24 h that was maintained for about 3 or 4 days, after which the LD50 returned to normal by the 7th day. The maximum LD50 reached was dependent on the first dose, but even a minute first dose, 0-004 ml/kg, had a significant effect. The same phenomenon was confirmed in rats. Administration of promethazine before doseing with CCl4 did not have this effect, nor did an ether anaesthetic.     

Interaction of hypoxia and carbon tetrachloride toxicity in hepatocyte monolayers

The toxicity of carbon tetrachloride (CCl4) in monolayer cultures of primary hepatocytes was investigated at oxygen concentrations that prevail in the liver under conditions that range from normoxia to hypoxia: 0.5, 1, 2, and 20% O2. CCl4 was administered in the vapor phase at concentrations that produce aqueous concentrations at 37 degrees C of 0.4, 2.0, and 4.0 mM. Damage was assayed by leakage of aspartate transaminase and the inclusion of Trypan Blue immediately after the 2-hr incubation and after an additional 6-hr incubation in 20% O2. Only in the case of 0.5% O2 and 4 mM CCl4 were the monolayers damaged (18%) immediately after the 2-hr exposure; all other exposed cells were undamaged at that time point and the dose response of cell death as a function of CCl4 and oxygen concentration was not evident until the 6-hr time point. The monolayers exposed to 4 mM CCl4 and 1, 2, or 20% O2 exhibited little immediate damage but were all 100% dead 6 hr later. The monolayers exposed to 2 mM CCl4 and 0.5, 1, 2, or 20% O2 were 53, 48, 40, and 22 +/- 2% dead after 6 hr, respectively. These results suggest that effects of CCl4 exposure, for example alterations in the function or synthesis of essential proteins, require several hours to affect cell viability.     

Hepatoprotective treatment attenuates oxidative damages induced by carbon tetrachloride in rats

The present study evaluated the hepatoprotective effect of an N-acetyl dl-methionine + choline chloride + caffeine + thiamine hydrochloride + nicotinamide + pyridoxine hydrochloride compound at doses of 0.2, 0.6 and 1.0 mL/kg of b.w., and the assessment was done by the investigation of serum-enzymatic activity, metabolic functions of the liver and histophatological changes in female Wistar rats, which were subjected to experimental intoxication with CCl₄. One hundred and nineteen rats were randomly distributed into 17 groups, performing five different treatments, being evaluated seven animals per treatment in four periods: 2, 4, 6 and 8 days after CCl₄-induced intoxication. Treated rats with the hepatoprotective medicine (HM) presented a significant reduction in infiltration of inflammatory cells, steatosis, necrosis and liver congestion when compared to non-treated rats (control). Beside these results, the treatment showed a positive effect on circulatory alterations in the intoxicated animals, with reduction of spleen and renal congestion, as well as, promotion of a significant improvement in ALT, AST, LDH, ALP, GGT enzymatic serum activity reduction and in recovering liver function regarding the metabolism of urea, triglycerides and glucose. These findings indicate therapeutic usefulness of the compound when administered at dose 0.6 and 1.0 mL/kg of b.w. in female Wistar rats.     

Liver hepatocyte mitotic activity after a single injection of phenobarbital in immature male rats

In contrast to multiple injections of phenobarbital, a single injection of 50 mg/kg body wt of phenobarbital into immature male rats results, after a transient increase in hepatocyte mitotic activity, in a marked decrease in hepatocyte mitotic activity to below control levels by day 3, followed by a return to control levels by day 5. This unusual pattern of hepatocyte mitotic activity can be called forth again by a second injection of 50 mg phenobarbital/kg body wt. However, a single injection of 50 mg/kg body wt of phenobarbital into immature male rats results in a pattern of change of liver wet weight, protein, and aminopyrine demethylase activity which is similar to that observed after multiple injections of phenobarbital, except that the changes are smaller in magnitude. Liver wet weight, protein, and aminopyrine demethylase activity increase and reach a peak within two days after phenobarbital injection, and then they return to control levels by five days. The same pattern of change in liver wet weight, protein, and aminopyrine demethylase activity can be elicited again by a second injection of 50 mg phenobarbital/kg body wt.     

Urinary excretion of alpha-fetoprotein in rats on a cirrhogenic carbon tetrachloride regimen.

Alpha-fetoprotein was detected in the serum and urine of 2- to 9-mth-old rats subjected to protracted CCl4 poisoning. During the first 3 mth of the experiment, urinary excretion of AFP was found in 30-40 per cent. of the animals, increasing to 70 per cent. thereafter. The liver lesions progressed from acute parenchymal necrosis to cirrhosis, but hepatocellular carcinomas did not develop. Uptake of tritiated thymidine by the hepatocytes increased significantly but was constant throughout the experimental period. The findings are compared to the observations made during 3mDAB-induced hepatocarcinogenesis in the rat.     

Manganese induced hepatic lesions in carbon tetrachloride pretreated rats.

Manganese sulphate (6 mg/kg) was administered intraperitoneally daily for 30 days in carbon tetrachloride pretreated rats. Histological and histochemical studies in liver tissue revealed extensive damage to hepatic parenchyma in these rats as compared to lesions produced by manganese sulphate alone. These findings suggest that workers, with liver dysfunction ergated in manganese industry may be more susceptible to the toxic effects of this metal.     

Effect of tryptophan on hepatoma and host liver of rats: Influence after treatment with hypertonic sodium chloride and carbon tetrachloride

Female inbred Buffalo rats bearing intrahepatically transplanted hepatoma 5123 were subjected intraperitoneally to the acute administration of hypertonic NaCl or CCl₄ followed by a tube-feeding of l-tryptophan. The responses in terms of changes in polyribosomal aggregation and protein synthesis (in vitro) of host liver and hepatoma were evaluated. While treatment with hypertonic NaCl or CCl₄ caused disaggregation of polyribosomes and inhibition of protein synthesis in both host liver and hepatoma, the subsequent administration of tryptophan caused some improvement in both parameters in host liver but not in hepatoma. Administration of hypertonic NaCl alone caused a decrease in [¹⁴C]orotate incorporation into poly(A)-mRNA of host liver and hepatoma, whereas administration of tryptophan after hypertonic NaCl caused a significant improvement in host liver alone. Following the tryptophan administration, the activities of nuclear DNA-dependent RNA polymerases I and II, and of nuclear-envelope nucleoside triphosphatase, as well as labeled nuclear RNA release in vitro were slightly elevated in host liver but not in hepatoma. Tryptophan-related compounds, 5-hydroxy-dl-tryptophan, 5-fluorotryptophan, indole, and 3-hydroxyanthranilic acid, when administered in place of l-tryptophan, did not appreciably affect polyribosomal aggregation or protein synthesis in vitro in host liver or hepatoma.     

Influence of carbon tetrachloride or riboflavin on liver carcinogenesis with a single dose of aflatoxin b1.

Liver carcinogenesis with a single dose of aflatoxin B1 (7 mg/kg body weight) has been investigated in a group of female Wistar strain rats by repeated biopsies and necropsies. Another group received a subsequent intoxication with carbon tetrachloride by inhalation (approximately 200 doses) and another one was overloaded with riboflavin (25 parts/10(6) in drinking water). The frequency of hepatomata was almost equal in the aflatoxin and aflatoxin-carbon tetrachloride group. It was lowere in the riboflavin-aflatoxin group. In these 3 groups cirrhosis was never present in neoplastic livers. Megalocytosis was the first lesion observed. All tumoral livers had previous or concomitant megalocytosis. This modification was about as frequent, intense and widespread in aflatoxin-CCl4 and aflatoxin groups but appeared much earlier, as did the first hepatoma, in the aflatoxin-CCl4 group. It was less frequent, less intense and less widespread in the riboflavin-aflatoxin group than in the aflatoxin group. There was also a lower frequency of hepatomata in the riboflavin-aflatoxin group, but the difference was not significant due to the too small number of animals involved. The facts are not a proof of the existence of an obligatory link between megalocytosis and carcinogenesis since a slight megalocytosis was observed in the riboflavin group not affected by the neoplastic process. However, the simplest explanation of our results would be to consider that the potential tumour cells are located among the megalocytic cells, without admitting that every megalocyte is obligatorily a precancerous cell. CCl4 seems to act in shortening the time of appearance of megalocytosis. The protective effect of riboflavine should be regarded with more caution.