Single Dose Of Diethylnitrosamine Research Articles

The role of N-sulfation in the N-hydroxy-2-acetylaminofluorene-mediated outgrowth of diethylnitrosamine-initiated hepatocytes to gamma-glutamyltranspeptidase-positive foci in male rat liver.

The ability of N-hydroxy-2-acetylaminofluorene (N-OH-AAF) to promote the appearance of gamma-glutamyltranspeptidase-positive (GGT+) foci initiated by diethylnitrosamine (DEN) was studied in a slightly modified Solt and Farber protocol. This protocol consisted of the following treatments: initiation with a single dose of DEN followed by selection/promotion with several non-necrogenic doses of N-OH-AAF and partial hepatectomy. Treatment with N-OH-AAF resulted in a 25-fold increase of the liver volume occupied by GGT+ cells as compared to controls. The role of N-sulfation of N-OH-AAF in the GGT+ foci-selecting activity of N-OH-AAF was studied using the sulfotransferase inhibitor pentachlorophenol (PCP). Inhibition of the N-sulfation pathway with PCP during selection with N-OH-AAF resulted in a greater than 80% decrease in the volume occupied by GGT+ cells, without effects on the number of GGT+ foci generated with this protocol. Also, PCP reduced the number of so called oval and bile duct cells generated by the N-OH-AAF/partial hepatectomy treatment. It is concluded that N-sulfation of N-OH-AAF is responsible for the N-OH-AAF-mediated outgrowth of DEN-initiated hepatocytes to preneoplastic GGT+ foci.

The influence of food intake on the development of diethylnitrosamine-induced liver tumours in mice.

The aim of this study was to determine whether a dietary restriction, which significantly decreases body weight gain, also influences the development of diethylnitrosamine (DEN)-induced liver tumours in Swiss mice. At birth, mice were injected i.p. with a single dose of DEN (0.4 mumol/g body wt); negative control mice were sham injected. After weaning the animals received a stock diet either ad libitum (control group) or at 30% restriction (restricted group). A positive control group was fed ad libitum and received phenobarbital (500 p.p.m.) in their drinking water. At 12 weeks of age, glucose-6-phosphatase (G6Pase)-deficient foci were present in the liver of 80% of the control animals but only in 32% of the restricted group. Quantitatively, restricted animals had fewer foci per unit volume liver and these were smaller than in the control animals. By 36 weeks of age, hepatocarcinomas were seen in 100% of the control mice while in the restricted group there were no such malignant lesions and only 32% showed adenomas. The results clearly show that restriction of food intake inhibits promotion and progression of induced liver tumours. Amongst other uses, this model permits the study of the effect of dietary restriction on liver tumours, at an early stage.

Failure of mitogen-induced cell proliferation to achieve initiation of rat liver carcinogenesis.

Experiments were designed to determine whether mitogen-induced cell proliferation is as effective as regenerative cell proliferation in achieving initiation of liver carcinogenesis. To test this hypothesis male Wistar rats were injected with a single dose of diethylnitrosamine (DENA) or N-methyl-N-nitrosourea (MNU) during the peak of DNA synthesis following the administration of the liver mitogen, lead nitrate, after partial hepatectomy (PH) or a necrogenic dose of CCl4. The initiated hepatocytes were monitored as gamma-glutamyltransferase (GGT)-positive foci using a 2-week selection regimen consisting of 0.03% 2-acetylaminofluorene (2-AAF) coupled with a necrogenic dose of CCl4. The results indicate that unlike compensatory cell proliferation such as that induced by PH or CCl4, mitogen-induced cell proliferation did not result in any initiated hepatocytes despite the fact that in both types of models the extent of liver cell proliferation at the time of the administration of the carcinogen is similar.

Changes in nucleolar transcriptional activity and nuclear DNA content during the first steps of rat hepatocarcinogenesis.

Two complementary genetic parameters were followed in liver parenchymal cells during the first steps of rat hepatocarcinogenesis: the expression of nucleolar genes estimated from their silver stainability and the nuclear DNA content determined after Feulgen staining. Putative preneoplastic lesions as foci and nodules were induced by the triphasic 'Gerlans protocol'. Initiation with a single dose of diethylnitrosamine (DEN) was followed by a selection of initiated cells with 2-acetylaminofluorene (2-AAF) in combination with a single necrogenic dose of CCl4 as a proliferative stimulus. Finally after 1 week of normal diet, the animals were treated or not with phenobarbital (PB) for periods up to 2 months. Serial sections were analysed after silver staining (AgNO3), methyl-green--pyronin staining (Unna-Brachet) and Feulgen staining with densitometric and morphometric methods. Silver staining, which is known to stain an acidic protein associated with rRNA synthesis, increased gradually with the duration of the PB treatment. Morphometry revealed an increase in both nucleolar and nuclear volume; the fraction of nuclei with one nucleolus also increased. These results seem to point towards an increase of nucleolar activity in the early steps of PB promotion. Moreover, this shift cannot be ascribed to an increase of DNA content. Indeed, a parallel study on neighbouring sections stained with Feulgen revealed a shift towards a population of diploid nuclei, in contrast to normal liver cells, which are mostly tetraploid. The observed diploidisation may therefore provide a functional advantage for the expansion of putative preneoplastic cells.

DI- n-Octyl phthalate (DOP), a relatively ineffective peroxisome inducing straight chain isomer of the environmental contaminant DI(2-ethylhexyl)phthalate (DEHP), enhances the development of putative preneoplastic lesions in rat liver

Di- n-octyl phthalate (DOP) is the straight chain isomer of di(2-ethylhexyl) phthalate (DEHP) which is a widely used plasticizer and an environmental contaminant. DEHP is a strong inducer of peroxisome proliferation in rat liver. This is significant since other compounds which are strong inducers of peroxisome proliferation have been reported to be weak carcinogens (Reddy, J.K. and Lalwani, N.D., CRC Crit. Rev. Toxicol., 12 (1983) 1). In contrast to DEHP, DOP causes little or no induction of liver peroxisomes (Mann, A.H. et al., Toxicol. Appl. Pharmacol., 77 (1985) 116, and Gray, T.J.B. et al., Toxicology, 28 (1983) 167). In the current study the ability of 1% DOP to promote the development of putative preneoplastic lesions was evaluated. The effect of feeding 0.5% DEHP as well as equimolar amounts of its 2 major metabolites, mono(2-ethylhexyl)phalate (MEHP) and 2-ethylhexanol (2-EH) were also investigated. GGT+ foci were initiated in the livers of Sprague-Dawley male rats with a single dose of diethylnitrosamine (DEN) following partial hepatectomy. The control group of rats was fed a semipurified diet (Co) for 10 weeks while the experimental groups received the semipurified diet containing the respective compounds. Induction of peroxisome proliferation was monitored by carnitine acetyltransferase (CAT) levels. DOP treatment resulted in a 6-fold increase in the number of GGT+-foci (20.8 ± 4.0 vs. 3.5 ± 1.3; P < 0.05). This was accompanied by no change in liver weight and only a slight increase in CAT activity when compared with control animals. In contrast to DOP, 2-EH produced essentially no effect with regard to number of foci, peroxisome proliferation or liver weight. DEHP and MEHP induced significant peroxisome proliferation and hepatomegaly but the number of foci were significantly lower than in 2-EH-treated rats. The mechanism for the promoting ability of DOP is not clear but would not appear to be related to peroxisome proliferation. Because of the close similarity of chemical structure and metabolism between DOP and DEHP, it is possible that studies to define the mechanism of DOP induced promotion might also serve to further clarify the mechanism of DEHP induced carcinogenesis.

The effect of single versus split doses of diethylnitrosamine on the induction of gamma-glutamyltranspeptidase-foci in the livers of adult and juvenile rats

The induction of gamma-glutamyltranspeptidase (GGT)-foci by single and by split doses of diethylnitrosamine (DENA) was evaluated in the livers of juvenile and young adult male, Sprague-Dawley rats. A single dose of DENA was administered at either 32, 41, 46, 52 or 56 days of age and followed by a promoting regimen of sodium phenobarbital in the drinking water. In 32 days old rats, DENA resulted in a higher incidence of GGT-foci/cm3 than was observed when it was administered to 41 or 46 day old rats. The same dose of DENA was inactive in 52 or 60 day old rats. In rats initiated with DENA on day 32 of age, starting the phenobarbital promotion at 41 days of age resulted in a higher incidence of GGT-foci than when the phenobarbital treatment was begun at 60 days of age. When the dose of DENA was split into five daily doses of DENA starting on day 32 of age, the incidence of GGT-foci/cm3 was equivalent to the single dose given on day 32 of age. However, when the five daily doses were started on 48 days of age, the incidence of GGT-foci/cm3 was less than the five doses of DENA started on day 32 of age. Hence, juvenile rats were more sensitive to both single and split doses of DENA than adult rats. The dose-response relationship was also determined in juvenile rats for a single and for up to 64 daily doses of 3 mg/kg DENA started on day 32 of age. The dose-response relationship for a single dose of 3-96 mg/kg DENA was equivalent to the relationship of one to 32 daily 3 mg/kg doses. Thus, low daily doses of DENA were additive when started in juvenile rats. Neither a threshold nor a plateau was obtained for the dose-response relationship of DENA initiation of GGT-foci.

Dinitrotoluene isomer-specific enhancement of the expression of diethylnitrosamine-initiated hepatocyte foci.

Technical grade dinitrotoluene (TDNT) was shown to be a potent hepatocarcinogen in rats; however, ambiguous results were obtained from bioassays which evaluated 2,4-DNT, the principal isomer in the technical mixture. The present studies were designed to determine the relative hepatocyte foci promoting activity of TDNT and the primary isomers present in the technical mixture, 2,4- and 2,6-DNT. A rat hepatic initiation-promotion protocol was used in which male Fischer-344 rats were initiated with a single dose of diethylnitrosamine (DEN) (150 mg/kg, i.p.) and permitted to recover for 2 weeks. Following the recovery period, the animals were fed diets containing TDNT,2,4-DNT,2,6-DNT or phenobarbital (PB). The TDNT animals were killed after 3 or 6 weeks of feeding and the 2,4-DNT-,2,6-DNT-and PB-treated animals were killed after 6 or 12 weeks of feeding. Appropriate DEN and DNT controls were also killed at each time point. Sections from three liver lobes of each animal were stained for gamma-glutamyl transferase (GGT) and the number of GGT+ foci per cm3 (Nv) was calculated using stereological methods. TDNT feeding produced a dose-dependent increase in GGT+ foci (Nv) at 3 and 6 weeks relative to both DEN and TDNT controls. Administration of 2,4-DNT and PB produced time-dependent increases in GGT+ foci (Nv), while 2,6-DNT produced dose- and time-dependent increases. Unlike 2,4-DNT and PB, the high dose (14 mg/kg) of 2,6-dNT produced an increase in GGT+ foci in the control groups and in mean foci volume relative to the DEN control. These results establish that TDNT, 2,4-DNT and 2,6-DNT have hepatocyte foci promoting activity and that 2,6-DNT is approximately 10 times more potent than 2,4-DNT. In addition, TDNT administration neither alters hepatocyte replication following partial hepatectomy nor acts as a 'growth selection' agent in the Solt-Farber 'growth selection' model suggesting that differential effects on hepatocyte replication are not responsible for the promoting activity of TDNT. Based on previous initiation study results from our laboratory and the present data, 2,6-DNT appears to be a complete hepatocarcinogen while under the conditions of these studies 2,4-DNT is an apparent 'pure promoter'. These results provide an explanation for the conflicting DNT bioassay results.

DNA ethylation in hamster tissues during subchronic diethylnitrosamine administration and in the hamster trachea after acute diethylnitrosamine administration.

Formation of O6-ethylguanine (O6EG) in trachea DNA was measured 12 h after acute i.p. administration of 50, 100 and 200 mg diethylnitrosamine (DEN)/kg body wt to Syrian golden hamsters. Purine bases were fractionated by h.p.l.c., and ethylated guanines were quantified optically by fluorescence spectrophotometry. Significant levels of this promutagenic base were found after the various single doses of DEN. O6EG in trachea DNA was also measured at various times up to 48 h after an acute i.p. dose of 200 mg DEN/kg body wt. The maximum level of O6EG was detected 12 h after DEN treatment. A rapid decrease in O6EG concentration was seen in trachea DNA between 12 and 24 h, but only a negligible decrease was detected from 24 to 48 h post-treatment. The formation and accumulation of O6EG in trachea, liver, lung and kidney DNA were determined in hamsters treated subchronically with DEN, 20 mg/kg body wt, s.c. twice weekly up to 8 weeks. O6EG accumulated to significant levels in trachea and liver DNA. 7-Ethylguanine did not accumulate in the DNA of any of the organs studied during subchronic DEN exposure. The formation and persistence of O6EG in trachea DNA of DEN-treated hamsters correlated with the sensitivity of this tissue to the carcinogenic action of DEN.

Bile ductular cells and the phenotypic heterogeneity of the population of hepatic non-parenchymal epithelial cells induced in rats by chemical carcinogens

Single doses of diethylnitrosamine, N-hydroxy-2-acetylaminofluorene or N-methyl-N-nitrosourea were administered to rats, before or after obstruction of the common bile duct, and liver sections were stained for alpha-fetoprotein, albumin and glucose-6-phosphatase. In these animals, cells expressing hepatocytic traits were not observed in the resulting expanded population of non-parenchymal epithelial cells. A derivation of non-parenchymal epithelial cells with hepatocytic traits from bile ductular cells is not supported, but not completely ruled out, by these findings. In rats with an obstructed bile duct and administered a single carcinogen dose, serum alpha-fetoprotein was slightly increased, to levels comparable with those occurring after a partial hepatectomy. In these rats, and in partially hepatectomized rats, the cellular source of serum alpha-fetoprotein was not apparent, since no alpha-fetoprotein-positive cells were detected in their liver.

Concentration-dependent inhibition of development of GGT positive foci in rat liver by the environmental contaminant di(2-ethylhexyl) phthalate.

The ability of di(2-ethylhexyl) phthalate (DEHP), a widely used plasticizer and environmental contaminant, to suppress development of putative preneoplastic lesions in rat liver was evaluated. gamma-Glutamyl transpeptidase-positive (GGT+) foci were initiated in the livers of Sprague-Dawley male rats with a single dose of diethylnitrosamine (DEN) following partial hepatectomy. Promotion of foci was commenced by feeding a choline-deficient diet (CD). A group of control rats was fed a choline-supplemented diet (CS). The ability of DEHP to suppress the emergence of GGT+ foci was evaluated by feeding additional groups of rats the CD diet containing either 0.1%, 0.5%, 1.0% or 2.0% DEHP. The CD diet promoted the number of GGT+ foci above levels in control livers. Inclusion of the plasticizer to the levels of 0.5%, 1.0% and 2.0% in the CD diet effectively inhibited the appearance of the foci. However, DEHP was unable to inhibit the promoting effect of the CD diet at a concentration of 0.1%. DEHP's ability to block development of GGT+ foci correlated with its ability to increase liver weight and to induce carnitine acetyltransferase (EC 2.3.1.7), a marker of peroxisome proliferation.

Concentration-Dependent Inhibition of Development of GGT Positive Foci in Rat Liver by the Environmental Contaminant Di(2-Ethylhexyl) Phthalate

The ability of di(2-ethylhexyl) phthalate (DEHP), a widely used plasticizer and environmental contaminant, to suppress development of putative preneoplastic lesions in rat liver was evaluated. gamma-Glutamyl transpeptidase-positive (GGT+) foci were initiated in the livers of Sprague-Dawley male rats with a single dose of diethylnitrosamine (DEN) following partial hepatectomy. Promotion of foci was commenced by feeding a choline-deficient diet (CD). A group of control rats was fed a choline-supplemented diet (CS). The ability of DEHP to suppress the emergence of GGT+ foci was evaluated by feeding additional groups of rats the CD diet containing either 0.1%, 0.5%, 1.0% or 2.0% DEHP. The CD diet promoted the number of GGT+ foci above levels in control livers. Inclusion of the plasticizer to the levels of 0.5%, 1.0% and 2.0% in the CD diet effectively inhibited the appearance of the foci. However, DEHP was unable to inhibit the promoting effect of the CD diet at a concentration of 0.1%. DEHP's ability to block development of GGT+ foci correlated with its ability to increase liver weight and to induce carnitine acetyltransferase (EC 2.3.1.7), a marker of peroxisome proliferation.

The quantitative analysis and stability of histochemical markers of altered hepatic foci in rat liver following initiation by diethylnitrosamine administration and promotion with phenobarbital

The stability and response of histochemical phenotypes of altered hepatic foci (AHF) were studied both in the presence and following the withdrawal of 0.05% phenobarbital (PB) treatment in rats previously given a single dose of diethylnitrosamine (DEN) 20-24 h following partial hepatectomy (PH). AHF were scored by their expression of three biochemical markers: gamma-glutamyl transpeptidase (GGT), adenosine triphosphatase and glucose-6-phosphatase (G6P). AHF demonstrated significant heterogeneity with respect to the marker alterations. The use of three markers in the present study confirmed the findings of our earlier study, which showed the maximal response of GGT+ AHF to PB administration following PH/DEN initiation and the stability of GGT+/AHF induced by the PH/DEN/PB regimen after the withdrawal of PB. In the regimen employed, the GGT marker alone scored the great majority of the AHF detected by all three markers. The frequency distribution of histochemical phenotypes remained relatively constant in AHF during continuous PB administration and in AHF promoted by PB followed by a 6-month period of feeding a diet containing no PB. These findings suggest that individual AHF remain phenotypically stable throughout the PB promotion phase, i.e., do not progress from one phenotype to another. In every marker class, the mean volume of AHF increased during continuous PB administration. These data illustrate the enhancing effect of PB on the growth of the AHF. The size of AHF continued to increase following the withdrawal of PB in the 3-month PB treatment group, but not in the animals treated for 4 months. A mechanism that may account for the differences in these two treatment groups is discussed.

Inhibition of phenobarbital and dietary choline deficiency promoted preneoplastic lesions in rat liver by environmental contaminant di(2-ethylhexyl)phthalate

The effect of di(2-ethylhexyl)phthalate (DEHP), a widely used plasticizer and environmental contaminant, on the emergence of gamma-glutamyltranspeptidase positive (GGT+) preneoplastic foci in the liver of rats fed promoting diets was studied. GGT+ foci were initiated in the liver of Sprague—Dawley male rats with a single dose of diethylnitrosamine (DEN) following partial hepatectomy. One series of control rats received saline vehicle alone. Promotion of foci was commenced by feeding: (1) a choline-deficient diet (CD); (2) a choline-supplemented diet (CS) containing 0.06% phenobarbital (CS + PHB); or (3) a CD diet containing 0.06% phenobarbital (CD + PHB). In the absence of initiation by DEN, dietary treatments did not increase the number of GGT + foci. In rats receiving DEN, each promoting regimen effectively increased the number of GGT+ foci above levels in control rats fed only the choline-supplemented diet. Inclusion of the plasticizer at a level of 2% in each of the dietary promotion treatments, however, effectively inhibited the appearance of the foci.

The natural history and dose-response characteristics of enzyme-altered foci in rat liver following phenobarbital and diethylnitrosamine administration.

Enzyme-altered foci (EAF) were induced in the liver of female rats by 70% partial hepatectomy (PH), followed by a single intragastric administration of diethylnitrosamine (DEN) at a dose of 10 mg/kg. The stability and response of these foci to various doses of the hepatic promoting agent, phenobarbital (PB), were studied. The number of gamma-glutamyltranspeptidase-positive (GGT+) EAF resulting from PH/DEN followed by PB (0.05%) administration for 1 week, 2 weeks, 1 month, 2 months, 3 months or 4 months did not significantly change when the administration of the promoting agent was followed by a 6-month period of a diet containing no PB. These data demonstrate the stability of the foci induced by the PH/DEN/PB regimen and indicate that the increased number of foci resulting from PB promotion in the absence of overt hepatic necrosis are not reversible on removal of the promoting stimulus. Chronic administration of dose levels of PB below 0.001% in the diet failed to demonstrate an increase in the number of EAF over the number in the control animals not promoted with PB. A linear increase in the number of EAF was observed when rats were chronically fed doses of PB ranging between 0.001% and 0.05% in the diet, whereas diet concentrations of PB greater than 0.05% did not result in any further increase in the number of EAF. The number of EAF resulting from PH/DEN followed by 0.05% PB in the diet increased during the first 3-4 months of promotion. Thereafter, the number of foci did not change despite the continued administration of PB for as long as 8 months. These data suggest the presence of an apparent threshold (no effect level) for promotion by PB and demonstrate the presence of a maximal response of EAF to this promoting agent after initiation by a single dose of DEN.

Early alterations in rat liver chromatin structure after a single dose of diethylnitrosamine.

In the chromatin of 24-h regenerating rat livers, derivative melting profiles are characterized by a high proportion of transitions above 90 degrees C. After the injection of diethylnitrosamine there is a rapid shift to lower melting temperatures. This is due to a rearrangement of the chromatin to higher amounts of nucleosomal components but possibly also a consequence of chemical modifications and conformational alterations of the DNA. In the nonregenerating liver essentially the same observations can be made, although reactions proceed significantly slower. These results are in good agreement with the observation that carcinogens are more active in tissues stimulated to rapid proliferation as compared to resting tissues.

Effects of varying the fat content of a choline-devoid diet on promotion of the emergence of γ-glutamyltranspeptidase positive foci in the liver of carcinogen-treated rats

Previous studies have shown that feeding a choline-devoid (CD) diet to rats is an effective promoter of liver carcinogenesis. In the present studies, we investigated the effects of CD diets containing different levels of fat (high, 15%; low, 4%) on the induction of foci of γ-glutamyltranspeptidase (GGT) positive hepatocytes in the liver of rats initiated with a single dose of diethylnitrosamine. In rats fed the high-fat CD diet for 4–6 weeks, a greater number of foci was induced than in rats fed similarly the low-fat CD diet. However, liver DNA synthesis and the rate of hepatocyte mitosis were not significantly different in rats fed the 2 CD diets, but were significantly higher than in rats fed a choline-supplemented diet. These results indicate that beside stimulation of liver cell proliferation, other factor(s) determine the efficacy with which a CD diet exerts its promoting action.

Alpha-1-antitrypsin in intracellular inclusions of diethylnitrosamine induced hepatomas of C57BLxC3H F1 mice.

Six large hepatic nodules obtained 46 to 74 weeks after a single dose of diethylnitrosamine (0.625 or 1.25 micrograms/gm) in infant C57BLxC3H F1 male mice were studied to elucidate the nature of intracytoplasmic inclusions in the hepatic cells of these nodules. By light microscopy, the nodules constituted a spectrum of lesions ranging from some which were well differentiated adenomas to others which were frank carcinomas. Round or oval eosinophilic intracytoplasmic inclusions were consistently seen in the well differentiated adenomatous lesions. Some of these inclusions were PAS positive and resisted diastase digestion while others were either negative or only weakly PAS positive. By electron microscopy, they were most commonly crystalline, contained a reticulated electron dense material and were located in the distended rough endoplasmic reticulum. On immunofluorescence the inclusions showed marked specific reactivity with antisera against human alpha-1-antitrypsin. The presence of alpha-1-antitrypsin in these inclusions was further supported by the resistance of these inclusions to digestion by trypsin or papain but not by the pepsin or pronase.

Proliferation of rat liver cells in preneoplastic nodules after stimulation of liver growth by xenobiotic inducers.

Several stimulators of adaptive liver growth such as phenobarbital, DDT, and butylhydroxytoluene have been found to promote the development of tumors from preformed carcinogenic lesions in rat liver (Peraino et al., 1975 and 1977). We have found that α-hexachlorocyclohexane (α-HCH), likewise, accelerates the manifestation of malignant liver tumors in rats after initiation of the carcinogenic process by a single dose of diethylnitrosamine (DENA). In order to get more insight into the nature of this promoting effect we studied the influence of α-HCH on cell proliferation in preneoplastic nodules initiated by prior treatment with DENA. 3H-thymidine was injected 1 hour before sacrifice, and auto-radiographs were prepared on histological sections. In the same sections nodules were identified by histochemical demonstration of γ-glutamyltransferase. Labelled cells (= cells involved in DNA synthesis) and mitoses were counted in both nodular and normal tissue. It was found that the rate of proliferation was severalfold higher in the nodules than in the surrounding healthy tissue. Inducers such as α-HCH appear to stimulate the proliferation of nodular cells. From these observations the following conclusions are drawn: (1) Increased rate of proliferation can be used as a diagnostic criterion to identify preneoplastic cells. Control of proliferation in these cells can be studied by the methods used. (2) The findings add support to the current concept that the preneoplastic nodules in the liver are predecessors of malignant cells. (3) The apparent stimulation of nodular cell proliferation by inducers such as α-HCH indicates promoting activity of these compounds and allows separation from initiating activity. Key wordsRat liverPreneoplastic nodulesCell proliferationα-hexachlorocyclohexaneCyproterone acetate

Influence of repeated liver regeneration on hepatic carcinogenesis by diethylnitrosamine in mice.

In mice given a single dose of diethylnitrosamine, a hepatonecrotic dose of carbon tetrachloride, 5 weeks after dosing with DEN and repeated 6 times at 4-weekly intervals, augmented the tumour yield in the livers. A single hepatonecrotic dose of CCl4 24 h before a single dose of DEN also increased the number of tumours produced. The effect of the repeated administration of CCl4 after the dose of DEN occurred in addition to, and was therefore independent of, the enhancing effect of a single dose of CCl4 before DEN. These results may be interpreted as implying (1) that the liver in the regenerative phase after a hepatonecrotic dose of CCl4 is more susceptible to an initiating action of DEN, i.e. produces more potential foci of tumour growth than in the normal liver and (2) that the repeated doses of CCl4 leading to repeated phases of regeneration, after the dose of DEN, provide a promoting stimulus.

Repeated partial hepatectomy as a promoting stimulus for carcinogenic response of liver to nitrosamines in rats.

Partial hepatectomy 24 h before a single i.p. dose of dimethylnitrosamine, diethylnitrosamine or ethylmethylnitrosamine increased the carcinogenic response in the liver of rats as determined by the number of tumours and the number of "focal proliferations" produced. Secondly, in rats given a single i.p. dose of diethylnitrosamine, 3 partial hepatectomies 5, 10 and 15 weeks after dosing the animals increased the carcinogenic response in the liver. The stimulus of repeated partial hepatectomy therefore appears to act as a "promoting agent" for liver carcinogenesis, that is if the single dose of diethylnitrosamine is regarded as an "initiating agent" in the terms of the two-stage hypothesis.