The variations of S-adenosyl-L-methionine content modulate hepatocyte growth during phenobarbital promotion of diethylnitrosamine-induced rat liver carcinogenesis

A decrease in liver S-adenosyl-L-methionine (SAM) content and an increase in ornithine decarboxylase (ODC) activity occurred between the 2nd and the 5th week after starting 2-acetylaminofluorene (AAF) feeding in diethylnitrosamine (DENA)-initiated rats. These rats then received a 0.05% phenobarbital (PB)-containing diet for 18 weeks after the end of AAF feeding. Two weeks after starting AAF, an increase in the hepatocyte labeling index (LI) also occurred in gamma-glutamyl-transpeptidase (GGT)-positive foci and surrounding tissue. LI returned to control values in a few days in surrounding tissue, while it remained high for at least 4 weeks in the foci. Analogous changes were observed, but for a shorter period of time, in the rats subjected to partial hepatectomy (PH) plus AAF, in which no GGT-positive foci developed. Twenty-four weeks after starting AAF, 30% of the liver was occupied by visible nodules. ODC activity and LI were high and SAM was low in nodules, but they were near to control values in surrounding liver. SAM administration reconstituted the liver SAM pool, inhibited ODC activity, and prevented visible nodule development. SAM inhibition of ODC activity occurred in vitro only after preincubation with liver homogenate and was enhanced by adenine, an inhibitor of methylthioadenosine (MTA) phosphorylase. MTA addition to the reaction of mixture for ODC determination was inhibitory. The SAM decrease in both liver and nodules was coupled with a decrease of MTA content. SAM administration caused MTA accumulation in the liver. It is suggested that liver SAM content by influencing MTA level, could be a rate-limiting factor for growth and promotion, through a modulation of polyamine synthesis.     

Correlation of changes in natural killer cell activity and glutathione S-transferase placental form positive hepatocytes in diethylnitrosamine-induced rat hepatocarcinogenesis.

To evaluate the induction of preneoplastic hepatic foci in relation to natural killer cell (NK) activity, we sequentially analyzed glutathione S-transferase placental form positive (GST-P+) hepatocytes and NK activity during diethylnitrosamine (DEN) and phenobarbital (PB)-induced hepatocarcinogenesis in Sprague-Dawley rats. Previous studies have shown that NK activity can modulate the carcinogenic process induced by chemical carcinogens. Newborn females were initially given a single intraperitoneal injection of 15 mg DEN/kg and three weeks later, they were treated with 500 ppm phenobarbital (PB). From week 3, PB was administered in drinking water for 9 weeks. Interim and terminal sacrifices were performed at weeks 12, 15 and 30. GST-P+ hepatocytes increased with age in DEN-treated rats, especially in the population of more than two GST-P+ hepatocytes. The NK activity of DEN-treated rats did not significantly differ from that of control rats until week 12, but it progressively decreased from week 15 to 30. These results indicate that changes of NK activity inversely correlated with the induction of preneoplastic hepatic foci. This strong correlation of decreased NK activity with enhanced induction of GST-P+ foci suggests that NK activity is important in the early progression of hepatocarcinogenesis in rats.     

Serum gamma glutamyl transferase as a specific indicator of bile duct lesions in the rat liver.

Serum gamma-glutamyl transferase (GGT), a marker of hepatic injury used extensively in humans, has been used rarely in rats because its specificity has not been previously defined. Studies were designed for investigation of the specificity of serum GGT activity with the use of cell type specific hepatotoxicants in Fischer 344 rats. Single necrogenic doses of CCl4, allyl alcohol (AA), and alpha-naphthylisothiocyanate (ANIT) were used to produce cell specific injury in centrilobular hepatocytes, periportal hepatocytes, and bile duct cells, respectively. Administration of CCl4 markedly increased serum activities of alanine aminotransferase (ALT), alkaline phosphatase (AP), and serum bile acid concentrations within 24 hours but had no effect on serum GGT activity. ANIT treatment increased serum GGT and AP activities and bile acid concentration 24 hours following administration. Allyl alcohol administration increased serum ALT activity but had no effect on GGT activity. Administration of ANIT in the diet at 0.01%, 0.022%, 0.047%, and 0.1% for 2, 4, and 6 weeks produced dose- and time-dependent increases in serum GGT activity which strongly correlated with quantitative increases in hepatic bile duct volume, which was determined morphometrically. These observations support the use of serum GGT activity in the rat as diagnostic of bile duct cell necrosis when increases are detected shortly after the insult and as an indicator of possible bile duct hyperplasia.     

Stereology of PCB 128-induced ultrastructural alterations in the rat liver

Hepatocyte cytoplasmic alterations were stereologically determined in male and female Sprague-Dawley rats fed PCB congener 128 (2,2',3,3',4,4'-hexachlorobiphenyl) in concentrations of 0.05, 0.5, 5, 50 ppm, or corn oil in diets daily for 13 weeks. A significant increase (p < 0.05) in the volume-fraction of smooth endoplasmic reticulum (SER) was measured in the female rats fed a diet containing 5 or 50 ppm of the congener and a significant increase was revealed in the male rats at doses of 0.5 and 50 ppm. Because drug metabolizing enzymes are bound to the SER, proliferated profiles may imply heightened enzyme activity necessary to metabolize the PCB. An elevation in volume-fraction of rough endoplasmic reticulum (RER) was measured in the hepatocytes of the male rats fed 5 ppm of the congener and none of the concentrations significantly enhanced the level of RER profiles in the females. The volume-fraction values of mitochondria, peroxisomes or lipid droplets of the hepatocytes in either the males or the females were not significantly different, as were the baseline volume-fraction of parameters studied between the male and the female rats. We determined for PCB 128, when administered in a diet to Sprague-Dawley rats, the no observable adverse effect level (NOAEL) is < 0.5 ppm.     

Histogenesis of dieldrin and DDT-induced hepatocellular carcinoma in Balb/c mice

Male, Balb/c mice were fed diets containing dieldrin (10 ppm) and DDT (100-175 ppm) for 75 weeks. Control and treated mice were serially killed and their livers analyzed by histological and histochemical procedures after 2, 4, 8, 16, 36, 52 and 75 weeks of exposure. Mice administered both chlorinated hydrocarbons initially responded with centrolobular hepatocytomegaly. The cells were characterized by decreased glucose-6-phosphatase and succinate dehydrogenase activity. At later periods 52 through 75 weeks, foci of phenotypically-altered hepatocytes were noted. The cells of these lesions were basophilic or clear-staining in hematoxylin and eosin-stained sections and displayed increased gamma glutamyl transpeptidase activity. In mice preloaded with iron dextran, cells of foci were negative for iron when the surrounding parenchyma was siderotic. Hepatocellular adenomas (HA) and carcinomas (HPC) were composed of cells with increased gamma glutamyl transpeptidase and glucose-6-phosphate dehydrogenase and decreased glucose-6-phosphatase and succinate dehydrogenase activity. In iron loaded mice, the cells of HA and HPC did not stain for iron in otherwise siderotic surroundings. Both hepatocellular foci and adenomas may be potential precursors of mouse hepatocellular carcinomas.     

大鼠再生肝对二乙基亚硝胺启动作用的敏感性

目的比较再生肝和正常肝对二乙基亚硝胺（ＤＥＮ）启动作用的敏感性。方法以２／３肝叶切除后８周末的大鼠为实验组,正常大鼠为对照组,作如下比较：肝重、常规组织学检查及３Ｈ－ＴｄＲ掺入试验;用修改的Ｓｏｌｔ－Ｆａｒｂｅｒ模型,通过对ＧＧＴ阳性癌前病灶的体视学测量,观察肝脏对ＤＥＮ的启动效应;在体内和体外（无血清原代培养肝细胞）经ＤＥＮ攻击后,以核酸原位缺口标记方法观察肝细胞ＤＮＡ的损伤程度。结果２／３肝叶切除后８周末的实验组肝脏的修复过程已完成,未见肝细胞继续增生的表现;经ＤＥＮ攻击后,实验组肝癌前病灶在数密度和体积密度上都显著高于对照组;无论在体内或体外接受ＤＥＮ攻击后,实验组肝细胞ＤＮＡ的损伤程度都显著大于对照组。结论即使再生过程已经完成,再生肝仍比正常肝具有较高的致癌敏感性,这与再生肝肝细胞在ＤＥＮ攻击后其ＤＮＡ损伤较重相关。     

Gamma-glutamyltransferase induction by glucocorticoids in rat liver: age-dependence, time-dependence, dose-dependence, and intralobular distribution

Postnatal responsiveness of rat-liver gamma-glutamyltransferase (GGT) to glucocorticoids (GC) has been defined by investigating: age-dependence, time-dependence, hormonal dose-dependence, and lag-time of the enzyme re-expression; half-life of the induced enzyme activity; dynamics of the enzyme reappearance in the liver tissue. Hydrocortisone-acetate (HC) or dexamethasone (DEX) were administered to the animals starting 1, 2, 3, 4, or 5 d before killing, at the doses of 25 micrograms or 1 microgram/(g b. w. x d), respectively. In 14 d old rats, after a lag-time of about 20 h (DEX) or 30 h (HC), GGT activity progressively increased up to 38 and 31 times the control value, respectively, at 5th d; the enzyme re-expression was linearly hormone dose-dependent; half-life of the induced enzyme activity was about 36 h. In 21 d old rats, GGT re-induction behaved as in 14 d old animals, except that the induced activity was about half that of each correspondent treatment. In 28 d old rats, a very low but significant GGT activity was re-expressed only after hormonal treatments longer than 48 h. In 35 and 77 d old rats, significant GGT activity was never re-induced. GGT was re-expressed in liver parenchyma, with a defined space-course. In 14 d old rats, GGT reappeared first in periportal areas, then in acinar zone 1, finally in acinar zone 2. While the animals were ageing, GGT re-expression occurred to lesser and lesser extents in liver tissues, because of a progressive space-restriction from acinar zones 1 and 2 to zone 1 and finally, in 35 d old rats, to periportal areas. In adults, GGT was re-expressed only by rare hepatocytes in periportal spaces. Acinar zone-3 hepatocytes did never re-express GGT, irrespectively of the animal age. Thus, 2 rat hepatocyte populations could be distinguished (1 responsive, the other unresponsive to GC for GGT re-expression), the relative proportion of which changes in favour of the unresponsive one while the animal ages. Hepatic GGT re-induction by GC, occurring after a long lag-time, does not follow the typical model of hormonal induction. Previous permissive cell changes seem to be required. Hepatocyte-GGT re-expression by GC appears to be inversely correlated with the differentiation level and the cytochrome P-450 amount (activity) of the cell as limiting factors for the triggering of the enzyme induction.     

Induction of peroxisome proliferation in hepatocytes transplanted into the anterior chamber of the eye. A model system for the evaluation of xenobiotic-induced effects.

The effect of two hypolipidemic peroxisome proliferators, ciprofibrate and di(2-ethylhexyl)phthalate (DEHP), on hepatocytes transplanted into the anterior chamber of the eye was examined. Young male F-344 rats transplanted with dissociated hepatocytes were fed either a control diet or a diet containing 0.025% ciprofibrate or 2% DEHP. After 4-5 weeks of treatment, all rats were sacrificed and the transplanted liver cells and portions of homotopic liver were processed for light and electron microscopy and for immunofluorescence microscopy. Morphometric analysis of transplanted hepatocytes showed a ninefold and fivefold increase in the volume density of peroxisomes in ciprofibrate and DEHP-fed rats, respectively. Indirect immunofluorescence studies revealed a marked induction of peroxisome-associated enzymes. From these data it is concluded that hepatic peroxisome proliferators cross the blood aqueous humor barrier and the transplanted hepatocytes in the anterior chamber of the eye retain their ability to recognize and respond to peroxisome proliferators.     

Influence of level of dietary protein on tryptophan-induced promotional activity in induction of gamma-glutamyl transpeptidase-positive foci of rat liver

The influence of varying the dietary protein content on the emergence of gamma-glutamyl transpeptidase (GGT)-positive foci in the livers of male rats fed elevated (2%) L-tryptophan (TRP) after being exposed to a hepatocarcinogen was investigated. Subtotal hepatectomies were performed, and 18 hr later the rats were treated with diethylnitrosamine (30 mg/kg). Ten days later four dietary groups were followed for 10 weeks: (1) control diet containing 21% protein (C); (2) control diet containing 5.3% protein (C-LP); (3) C + TRP; and (4) C-LP + TRP. Rats fed the C-LP diet developed heavier livers but fewer and smaller GGT + foci than did rats fed the C diet. Rats fed elevated TRP diets (C + TRP and C-LP + TRP) developed more and larger GGT + foci than did rats fed the regular control diets (C and C-LP), indicating that the promotional effect of elevated dietary TRP was similar at the two levels of dietary protein.     

Transplantation of fetal liver tissue suspension into the spleens of adult syngenic rats: effects of various mitogens and cytotoxins on cytochrome P450 (P450) isoforms expression and on P450 mediated monooxygenase functions.

Syngenic fetal liver tissue suspensions were transplanted into the spleens of adult male Fisher 344 inbred rats. Four months after surgery, transplant recipients and age matched control rats were treated with various mitogens (fluorene [FEN], fluorenone [FON] and 2-acetylaminofluorene [AAF]) or cytotoxins (allyl alcohol [AAL], bromobenzene [BBZ] and carbon tetrachloride [CCl4]) or the respective solvents 24 or 48 hours before sacrifice. The expression of three cytochrome P450 (P450) isoforms, 1A1, 2B1 and 3A2, within spleens and livers was assessed by immunohistochemistry and P450 mediated monooxygenase functions in spleen and liver 9000 g supernatants by the model reactions ethoxyresorufin O-deethylation (EROD), ethoxycoumarin O-deethylation (ECOD), and ethylmorphine N-demethylation (EMND). The orthotopic livers of both solvent treated transplant recipients and control rats displayed only in few lobules a slight P450 1A1, but in all lobules a moderate P450 2B1 and 3A2 expression, all mainly located in the hepatocytes around the central veins. Correspondingly, regular EROD, ECOD and EMND activities were observed. Each of the three mitogens increased the P450 1A1 expression in the hepatocytes of the perivenous zones of the liver lobules. FON administration caused an additional P450 1A1 immunostaining in the periportal areas, and AAF treatment a P450 1A1 expression in bile duct epithelia. Also the staining for P450 2B1 and 3A2 in the hepatocytes of the perivenous and intermediate zones of the liver lobules was intensified after treatment with any of the mitogens. The three model reactions were significantly increased within the livers after FEN and FON administration, whereas after AAF treatment only ECOD was enhanced, EROD remained unaffected and EMND was decreased. The cytotoxin AAL caused small lesions and fatty degeneration of hepatocytes only in some periportal areas. BBZ only produced a perivenous necrosis of single cells, whereas CCl4 caused complete necrosis of the centrilobular parenchyma. Immunohistochemically, AAL administration led to an increase in the P450 2B1 expression in the perivenous hepatocytes, whereas the staining for P450 1A1 was not affected and that for P450 3A2 was even decreased in the periportal areas. Due to AAL treatment EROD and EMND activities were not affected and ECOD activity was increased. BBZ administration caused a P450 1A1 expression in the periportal hepatocytes but a decrease in this staining of the perivenous cells. The number of hepatocytes positively stained for P450 2B1 and 3A2 in the perivenous and intermediate zones was diminished in comparison to the livers of solvent treated rats. After BBZ treatment, EROD and EMND activities were decreased, ECOD activity was not affected. CCl4 administration caused a strong reduction in the expression of all three P450 isoforms and in the activity of all three model reactions. Spleens of control rats displayed almost no P450 isoforms expression and P450 mediated monooxygenase functions, without as well as after treatment with the mitogens or cytotoxins. Similar to adult liver, the hepatocytes in the transplant containing spleens showed nearly no P450 1A1, but a noticeable P450 2B1 and 3A2 expression. No staining was observed within the bile duct cells of the intrasplenic transplants.     

Islet graft-induced changes of beta-hydroxybutyrate dehydrogenase and glucose-6-phosphatase activity in liver cells of diabetic recipient rats.

It is known that the liver is a favourable site for implantation of pancreatic islets since the grafted islets remain metabolically intact and provide long-term normoglycemia in diabetic animals. However, the long-term effects exerted by the grafted tissue on the host organ are not well defined. We therefore investigated by light and electron microscopy the effects of syngeneic islets on the host organ after intraportal transplantation into the liver of streptozotocin (STZ)-induced diabetic LEW.1W rats. In addition, tissue sections of graft-bearing liver were stained by enzyme histochemical methods for beta-hydroxybutyrate dehydrogenase (HBDH) and glucose-6-phosphatase (G6Pase). At 12 weeks after transplantation, the changes seen in the hepatocytes surrounding the grafted islets were hyperproliferation and accumulation of glycogen. Hepatocytes adjacent to the implanted islets displayed increased HBDH activity, whereas G6Pase activity was variable, either decreased or increased. Increased HBDH activity was also observed in the periportal region and in liver cells extending to the central veins. The results demonstrate that intraportal islet grafts, in addition to normalizing glucose homeostasis, exert remarkable effects on the liver parenchyma of experimentally diabetic recipient rats.     

Histochemical studies on the early proliferative lesion induced in the rat liver by aflatoxin

Male inbred Fischer rats were fed a diet containing 5 p.p.m. aflatoxin for 1, 3, 4½ and 6 weeks at which times groups were killed for histological and histochemical study. Aflatoxin produced a scattered individual cell necrosis of parenchymal cells by 1 week. At 3 weeks small basophilic proliferative foci were seen which increased in size and abundance to 6 weeks. These foci showed starvation-resistant glycogen, variable depletion of glucose-6-phosphatase, succinic dehydrogenase, aniline hydrogenase, membrane ATPase and acid phosphatase. At 6 weeks the foci showed the presence of gamma glutamyl transpeptidase and glucose-6-phosphate dehydrogenase. The basophilic foci were not preceded by other focal histological and histochemical change. The basophilic proliferative lesions are observed when an irreversible change has been induced in the liver. The role of such lesions in the histogenesis of hepatocellular carcinoma is discussed.     

Placental glutathione S-transferase (GST-P) as a new marker for hepatocarcinogenesis: in vivo short-term screening for hepatocarcinogens

Our laboratory has developed an in vivo short-term screening test for hepatocarcinogens based on quantitation of gamma-glutamyl transpeptidase (gamma-GT) positive foci. However, gamma-GT positive hepatocytes appear in periportal areas under a variety of circumstances apparently unrelated to hepatocarcinogenesis. Glutathione S-transferase placental type (GST-P), which is hardly detectable in normal rat liver, was recently demonstrated as a new marker protein for preneoplastic liver foci. In experiment I, rats were initially given a single dose (200 mg/kg) of diethylnitrosamine intraperitoneally and 2 weeks later were treated with test compounds for 6 weeks. All rats were subjected to partial hepatectomy at week 3. The long-term development of preneoplastic lesions was followed in rats for 50 weeks. The immunohistochemical investigation of GST-P binding and the histochemical demonstration of gamma-GT in serial sections revealed that almost all gamma-GT foci were GST-P positive, but 5-10% of GST-P foci could not be detected by gamma-GT staining. From week 8, many gamma-GT foci partially lost gamma-GT activity. However, no comparable disappearance of GST-P was evident in the lesions. All hepatocellular carcinomas (HC) found at week 50 consisted of GST-P positive HC cells. In contrast, 37.9% (11/29) of HC were negative for gamma-GT. In experiment II (in vivo short-term screening test for hepatocarcinogens), rats were treated in the same manner as for experiment I and killed at week 8. Fifty-eight chemicals were investigated for their potential to modify GST-P positive foci development.(ABSTRACT TRUNCATED AT 250 WORDS)     

Scanning electron microscopic surface morphology of isolated hepatocytes from normal and premalignant rat liver.

Scanning electron microscopy was performed on hepatocytes isolated after collagenase perfusion of livers from rats fed 2-acetylaminofluorene (AAF) in the diet for 6--8 weeks and on hepatocytes from control rats. The premalignant AAF-cells showed a greater variation in cell size and shape. They also exhibited a reduced number of microvilli and more blebs and other protrusions on the surface than hepatocytes from control animals.     

The sensitivity and heterogeneity of histochemical markers for altered foci involved in liver carcinogenesis.

Subcutaneous injection of iron dextran resulted in a hepatic siderosis within 2 weeks in rats, as previously reported for mice. Hepatic carcinomas as well as neoplastic nodules in rats were entirely or mainly free of stainable iron and, thus, could be readily identified histologically. In addition, early carcinogen-induced altered foci were resistant to iron accumulation. In rats fed 0.02% N-2-fluorenylacetamide (FAA) for 13 weeks, the number of iron-resistant foci identified following iron injection was the same as that observed with dietary iron overload. Histochemical investigation of enzymatic markers that have been used to identify foci in rats revealed that foci characterized by enzymatic reactions of positive gamma-glutamyl transpeptidase and decreased adenosine triphosphatase and glucose-6-phosphatase corresponded to those characterized by resistance to iron accumulation. However, in quantitative analysis of the early carcinogen-induced foci in rats given iron dextran following a diet containing 0.02% 2-FAA for 13 weeks, more lesions were detected by resistance to iron accumulation than by any of these other properties. There was considerable phenotypic heterogeneity among foci for the enzyme markers. It is concluded that resistance to iron accumulation is a more sensitive and reliable marker for early carcinogen-induced altered hepatocellular foci than is any other histochemical property.     

A 26-week carcinogenicity study of 2-amino-3-methylimidazo[4,5-f]quinoline in rasH2 mice

To evaluate the carcinogenic susceptibility of rasH2 mice to 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 7-week-old rasH2 mice and their wild-type littermates (non-Tg mice) of both the sexes were fed a diet containing 0 or 300 ppm IQ for 26 weeks. Microscopical examinations revealed that the proliferative lesions of the forestomach, including squamous cell hyperplasias, papillomas, and carcinomas, were frequently encountered in male and female rasH2 mice fed with IQ. In non-Tg mice, no significant differences in the incidence of forestomach lesions were observed between the 0 ppm and 300 ppm groups. Histopathological changes such as periportal hepatocellular hypertrophy and oval cell proliferation in the liver were more apparent in female rasH2 and non-Tg mice than in males, and the incidence of hepatocellular altered foci significantly increased in female rasH2 mice in the 300 ppm group as compared to that in the 0 ppm group. These results suggest that the carcinogenic potential of IQ can be detected in rasH2 mice by a 26-week, short-term carcinogenicity test.     

Acute viral hepatitis: morphologic and functional correlations in human livers

The usual histologic pattern in acute viral hepatitis (AVH) includes cellular abnormalities predominantly in the perivenular (zone 3) hepatocytes and changes interpreted as representing regenerative activity in the periportal (zone 1) hepatocytes. Enzyme histochemical and ultrastructural studies of livers of 12 patients with AVH were undertaken to see whether these features support the concept of regeneration of hepatocytes in zone 1. The swollen hepatocytes in the perivenular areas were hydropic, with dilated or eccentric rough endoplasmic reticulum and decreased or vesicular smooth endoplasmic reticulum; correspondingly, the glucose-6-phosphatase activity (reflecting, when present, intact and functional endoplasmic reticulum) was markedly decreased. Succinic dehydrogenase and diphosphopyridine nucleotide diaphorase activities, representing mitochondrial enzymes, were limited to the perinuclear or pericanalicular cytoplasm of swollen hepatocytes. gamma-Glutamyl transpeptidase activity was increased. The periportal hydropic hepatocytes were small and arranged in clusters displacing sinusoids. Ultrastructurally, these hepatocytes had nearly normal organelles but scanty smooth endoplasmic reticulum. Activities of the enzymes glucose-6-phosphatase, succinic dehydrogenase, and diphosphopyridine nucleotide diaphorase were weak, although glycogen was abundant. gamma-Glutamyl transpeptidase activity was scanty in these hepatocytes. These findings from enzyme histochemical and electron microscopic studies could be interpreted as evidence of functional deterioration of perivenular swollen hepatocytes and relative functional immaturity of periportal hydropic clustered hepatocytes, suggesting regeneration of zone 1 hepatocytes.     

Characterization of the promoting activity of thiobenzamide on liver carcinogenesis

To characterize the promoting activity of thiobenzamide (TB), a thiono-sulfur-containing xenobiotic, rats of both sexes were treated with the compound for 4 or 8 weeks after an initiating dose of diethyl-nitrosamine. The number, area (volume), and phenotypic complexity of the enzyme-altered hepatocyte foci were studied in serial sections stained with hematoxylin/eosin and reacted for glycogen, iron, and gamma-glutamyltranspeptidase activity. The TB-induced changes on the drug metabolizing systems were also investigated. The main findings were: When fed in a dose range of 500-2,000 mg/kg of diet, TB induced a number of foci greater than controls, especially in female rats. Benzamide, a major TB metabolite, was ineffective. The appearance of hepatocyte foci upon TB feeding was nearly synchronized. An increase of the phenotypic complexity of the hepatocyte foci occurred only during the first 4 weeks of TB administration; it correlated with an increase in size. The liver microsome content of cytochrome P-450 as well as the activity of many monooxygenases was decreased, some of the phase II reactions being increased. In conclusion TB behaves as an efficient promoter of liver carcinogenesis, possibly as a consequence of an induced adaptive response.     

二乙基亚硝胺诱发的变异肝细胞组化表型的研究

The histochemical changes of gamma-glutamyltransferase (gamma-GT), adenosine triphosphatase (ATPase), glucose-6-phosphatase (G-6-Pase) and ornithine carbamyltransferase (OCT) were studied in diethylnitrosamine (DEN) -induced and enzyme-altered liver cell lesions (Solt-Farber model) in rats. The number of altered liver cell foci tended to decrease after ceasation of 2-acetylaminofluorene (2-AAF); nevertheless, the number and size of the nodules increased rapidly within 20 weeks. The histochemical changes of most of the altered liver cell foci were focused on one or two kinds of enzyme activity (mostly gamma-GT and ATPase); while most of the nodules presented 3 or 4 kinds of histochemical changes, including OCT and G-6-Pase. It is concluded that some of those altered nodules of multi-enzyme changes might develop continuously to become tumors.     

Diuron lacks promoting potential in a rat liver bioassay

The promoting activity of the herbicide Diuron was evaluated in a medium-term rat liver carcinogenesis bioassay that uses as endpoint immunohistochemically identified glutathione S-transferase positive (GST-P+) foci. Male Wistar rats were allocated to the following groups: G1 to G6 were initiated for liver carcinogenesis by a single dose of diethylnitrosamine (DEN, 200 mg/kg) while groups G7 and G8 received only 0.9% NaCl (DEN vehicle). From the 2nd week animals were fed a basal diet (G1 and G7) or a diet added with Diuron at 125, 500, 1250, 2500 and 2500 ppm (G2 to G5 and G8, respectively) or 200 ppm Hexaclorobenzene (HCB; G6). The animals were submitted to 70% partial hepatectomy at the 3rd week and sacrificed at the 8th week. The herbicide did not alter ALT or creatinine serum levels. No conspicuous GST-P+ foci development was registered in non-initiated rats fed Diuron at 2500 ppm. While DEN-initiated animals fed Diuron at 1250 or 2500 ppm developed mild centrilobular hypertrophy, DEN-initiated HCB-fed animals showed severe liver centrilobular hypertrophy and significant GST-P+ foci development. These findings indicate that the medium-term assay adopted in this study does not reveal any liver carcinogenesis initiating or promoting potential of Diuron in the rat.