Cytological and quantitative cytochemical changes in the hepatocyte population of newborn rats following hydrocortisone administration

Changes have been assessed in cytological and quantitative cytochemical parameters of the hepatocyte population of newborn rats under glucocorticoid stimulation. Administration of hydrocortisone-acetate at the dose of 25 micrograms/g b.w./d during the 2nd week of postnatal life, caused: 1. an increase of the liver weight and of average dry mass, protein content, and volume of the hepatocytes; 2. a decrease of the number of hepatocytes per mg of liver tissue; 3. a reduction of the mitotic activity in liver parenchyma; 4. a gain in number of hepatocytes per liver lower than under normal conditions; 5. an increase of frequency of binuclear cells; 6. an increase of DNA-Feulgen per hepatocyte nucleus; 7. an increase per cell, greater than the mean protein increase per cell, in activity of arylhydrocarbonmonooxygenase and 7-ethoxycoumarin 0-deethylase, 2 enzymes dependent on cytochrome P-450. Induction of arylhydrocarbonmonooxygenase activity was prevalent in centrolobule. All the examined parameters, except that of DNA-Feulgen per nucleus and that of mitotic activity, changed strictly correlated with the duration of hormonal treatment. The values of a number of hepatocyte parameters (particularly: mean cell dry mass and volume, frequency of binuclear cells, enzymic activity) detected in the 12 d old rats after a 5 d long hormonal pretreatment, were in the range of those of animals 1 to 2 weeks older.     

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.     

Role of estrogens as promoters of hepatic neoplasia

The administration of estrogens to humans has been associated with the development of benign and possibly malignant hepatocellular neoplasms. This study was designed to investigate the mechanism of this association. We present a rat model that demonstrates that stilbestrol (DES) and ethinyl estradiol promote the development of hepatic neoplasms in rats previously initiated with diethylnitrosamine (DEN). Eighty male and 12 female Fischer-344 rats were given a single intraperitoneal injection of either DEN (200 mg. per kg. of body weight) or saline. Beginning 4 weeks after injection, the rats were given an estrogen or corn oil twice weekly for up to 50 weeks. Treatments were stopped at the time of sacrifice or 11 to 29 weeks prior to sacrifice. Estrogen treatments included high dose DES (5 mg. per dose), low dose DES (0.5 mg. per dose), and ethinyl estradiol (0.2 mg. per dose). Male and female rats given both DEN and high dose DES developed grossly visible hepatic hyperplastic nodules (mean, 9.1 per liver) after 20 weeks of DES. Nodules also developed if the onset of DES treatment was delayed until 28 weeks after initiation. Rats given DEN alone or DES alone did not develop nodules after 20 weeks. Microscopic hyperplastic foci also developed in rats given DEN plus DES, DES alone, and DEN alone. The foci in rats given DES alone were largely reversible on cessation of estrogen therapy. Mitotic activity in foci and nodules was prominent during estrogen therapy but declined markedly after cessation of therapy. Similar promoting activity of ethinyl estradiol was observed. Low dose DES was not effective in promoting tumor formation. The data indicate that estrogens promote hepatic neoplasia, perhaps by increasing hepatocyte mitotic activity and thereby facilitating the evolution of previously initiated cells into neoplastic clones. Comparison with human disease should be made with caution, especially because the estrogenic dose administered was approximately 200-fold the usual contraceptive dose in humans. However, the analogy between this model and the development of human oral contraceptive-associated hepatic tumors is evident. It is possible that some women have latent "initiated" cells that divide faster than the surrounding hepatocytes in response to estrogens.     

Hepatocyte proliferation is the possible mechanism for the transient decrease in liver injury during steatosis stage of alcoholic liver disease

Steatosis is a frequent pathologic stage in alcoholic liver disease (ALD). Although the mechanisms for increased susceptibility of steatotic liver to injury have been postulated, the ability of these hepatocytes to proliferate and withstand injury is unknown. There are conflicting reports on the status of hepatocyte regeneration following chronic alcohol ingestion. Hence, the objective of this study was to investigate the temporal dynamics between the pattern of liver injury and hepatocyte proliferation during the steatosis stage of ALD. Alcoholic steatosis was induced in male Sprague-Dawley rats by feeding an ethanol (EtOH)-containing Lieber-DeCarli liquid diet for a period of 5 weeks. Microvesicular steatosis was evident in H&E sections by three weeks in the EtOH-treated rats, which further developed into panlobular macrovesicular steatosis by 5 weeks. Plasma transaminase activities indicated progressive increase in liver injury peaking at 3 weeks with significant but mild decrease at 4 and 5 weeks. CYP2E1 protein and activity was significantly increased in EtOH-fed rats as measured by Western blot and pNP hydroxylation assay. PCNA analysis of liver sections indicated that EtOH-treated rats had a significantly higher number of cells in S phase of cell division at weeks 1 (3.20 +/- 0.19), 2 (7.03 +/- 0.92), and 3 (4.23 +/- 1.41) when compared to controls (1.5 +/- 0.22). NF-kappaB DNA binding and Cyclin D1 proteins increased significantly in the EtOH-treated rats corresponding with enhanced hepatic proliferation. These data suggest the transient decline in liver injury during alcoholic steatosis is due to enhanced NF-kappaB-dependent hepatocyte proliferation.     

Effects of the peroxisome proliferator di(2-ethylhexyl)phthalate on enzymes in rat liver and on carcinogen-induced liver altered foci in comparison to the promoter phenobarbital

The livers of rats given either the peroxisome proliferating hepatocarcinogen di(2-ethylhexyl)phthalate (DEHP) following initiation by 2-acetylaminofluorene (AAF) or the neoplasm promoter phenobarbital (PB) were studied for changes in 8 histochemical properties. Male F344 rats were fed 200 ppm AAF for 7 weeks to induce hepatocellular altered foci, and were then fed diets containing either no chemical, 12,000 ppm DEHP or 500 ppm PB for 24 weeks. In hepatocytes, DEHP increased alkaline phosphatase activity throughout the lobule, but reduced gamma-glutamyltransferase (GGT) activity in periportal hepatocytes. PB, in contrast, increased GGT activity in periportal hepatocytes. In foci that were induced by AAF, DEHP reduced the histochemical activity of GGT and did not increase the number, mean volume or volume % of foci detected by deficiencies in iron storage, glucose-6-phosphatase, adenosine triphosphatase or fibronectin. PB enhanced the expression of all 8 phenotypic abnormalities in foci such that either more profiles were detected or the area of foci was increased.     

Comparative effects of carcinogens on the induction of placental glutathione S-transferase-positive liver nodules in a short-term assay and of hepatocellular carcinomas in a long-term assay

The dose-dependent effects of three hepatocarcinogens were investigated by measuring the number and area of glutathione S-transferase placental form (GST-P)-positive foci and nodules appearing in the liver under short-term conditions (Experiment I) and evaluating the incidence of hepatocellular carcinoma after long-term chronic administration (Experiment II). For these purposes, three different doses of 2-acetylaminofluorene (2-AAF), 3'-methyl-4-dimethy-laminoazobenzene (3'-Me-DAB), and DL-ethionine (ethionine) were given to male F344 rats for 6 weeks after a single injection of diethylnitrosamine (DENA) in Experiment I or for 104 weeks without initiation by DENA in Experiment II. In Experiment I, the induction of GST-P-positive foci and nodules by 2-AAF and 3'-Me-DAB was clearly dose-dependent. In contrast, ethionine showed enhancing effects inducing GST-P-positive foci and nodules only in groups given the highest dose level. Similarly, in Experiment II, induction of hepatocellular carcinomas by 2-AAF and 3'-Me-DAB was clearly dose-dependent, whereas liver neoplasms were only induced by the highest dose level of ethionine. These results indicate that degree of induction of GST-P positive foci and nodules in a short-term in vivo test for liver carcinogens corresponds with the incidences of hepatocellular carcinomas revealed in a long-term in vivo assay.     

COMPARATIVE STUDY OF ABNORMALITY IN GLYCOGEN STORING CAPACITY AND OTHER HISTOCHEMICAL PHENOTYPIC CHANGES IN CARCINOGEN-INDUCED HEPATOCELLULAR PRENEOPLASTIC LESIONS IN RATS

A sequential comparison was made between abnormal glycogen storage and other histochemical phenotypic changes in hepatocellular precancerous lesions (altered foci and neoplastic nodules) during various stages in the process of development of cancer in rat liver. N-2-fluorenylacetamide was fed to male rats for 8 weeks and groups of rats were killed at the end of carcinogen feeding and at 12 and 24 weeks on control diet. Foci rich in glycogen storage accounted for a majority of all foci over the course of experiment, while foci devoid of glycogen storage, which were absent at the end of carcinogen feeding, gradually increased in number during maintenance. Glycogen-deficient lesions that might appear to arise from glycogen-rich lesions displayed hyper-basophilia demonstrated by toluidine blue reaction, but often lacked gamma-glutamyl transpeptidase activity. Resistance to iron accumulation was consistently shown in all precursor lesions for hepatocellular carcinoma in the siderotic liver regardless of abundance or absence of cellular glycogen. It was suggested that properties such as loss of glycogen storing capacity, hyperbaso-philia, and some cellular atypicality resembling those of carcinoma cells might be essential elements for malignant progression.     

异甘草酸镁干预肝纤维化大鼠肝细胞体积与数量的体视学

目的:探讨异甘草酸镁(MgIG)对四氯化碳(CCl4)致大鼠肝纤维化模型肝细胞数量与体积的影响.方法:雄性SD大鼠随机分为对照组、模型组、治疗组,治疗组给予CCl4皮下注射,同时每日腹腔注射MgIG?30 mg/?kg.各组大鼠在造模5周后取材,从每只大鼠等距抽选4个2 mm厚的肝组织块制作石蜡包埋切片,行Masson...     

Dexamethasone inhibits induction of liver tumor necrosis factor-alpha mRNA and liver growth induced by lead nitrate and ethylene dibromide.

We have recently demonstrated that a single injection of the mitogen lead nitrate to rats induced a rapid increase of tumor necrosis factor-alpha (TNF-alpha) mRNA in the liver and suggested that this cytokine may be involved in triggering hepatocyte proliferation in this model of direct hyperplasia. In this study, we examined whether a similar induction of liver TNF-alpha mRNA could be observed preceding the onset of hepatocyte proliferation induced by ethylene dibromide, another hepatocyte mitogen. In addition, we used dexamethasone, a well known inhibitor of TNF-alpha production, to determine whether its administration could suppress hepatocyte proliferation induced by lead nitrate and ethylene dibromide. A single intragastric administration of ethylene dibromide (100 mg/kg) to male Wistar rats enhanced liver TNF-alpha mRNA after 4 and 7 hours, which then returned to control levels by 24 hours. TNF-alpha mRNA was detectable only in a nonparenchymal cell fraction of the liver. Pretreatment of rats with a single dose of dexamethasone (2 mg/kg) 60 minutes before lead nitrate (100 mumol/kg) or ethylene dibromide completely abolished the increased levels of liver TNF-alpha mRNA induced by these agents. Inhibition by dexamethasone of TNF-alpha mRNA was associated with an inhibition of liver cell proliferation induced by these mitogens, as measured by [3H]thymidine incorporation into hepatic DNA, mitotic index, and DNA content. These results further support the hypothesis that TNF-alpha may be involved in triggering hepatocyte proliferation induced by primary mitogens.     

Comparative study of abnormality in glycogen storing capacity and other histochemical phenotypic changes in carcinogen-induced hepatocellular preneoplastic lesions in rats

A sequential comparison was made between abnormal glycogen storage and other histochemical phenotypic changes in hepatocellular precancerous lesions (altered foci and neoplastic nodules) during various stages in the process of development of cancer in rat liver. N-2-fluorenylacetamide was fed to male rats for 8 weeks and groups of rats were killed at the end of carcinogen feeding and at 12 and 24 weeks on control diet. Foci rich in glycogen storage accounted for a majority of all foci over the course of experiment, while foci devoid of glycogen storage, which were absent at the end of carcinogen feeding, gradually increased in number during maintenance. Glycogen-deficient lesions that might appear to arise from glycogen-rich lesions displayed hyperbasophilia demonstrated by toluidine blue reaction, but often lacked gamma-glutamyl transpeptidase activity. Resistance to iron accumulation was consistently shown in all precursor lesions for hepatocellular carcinoma in the siderotic liver regardless of abundance or absence of cellular glycogen. It was suggested that properties such as loss of glycogen storing capacity, hyperbasophilia, and some cellular atypicality resembling those of carcinoma cells might be essential elements for malignant progression.     

Isolation and enrichment of cells resistant to iron accumulation from carcinogen-induced rat liver altered foci

Enrichment of cells from rat liver iron-excluding foci induced by 2-acetylaminofluorene was performed using density gradients. Rats were continuously fed a diet containing the carcinogen for 8 to 13 weeks to induce altered foci that were iron excluding and positive for γ-glutamyl transpeptidase activity. At weekly intervals, and after loading with iron by subcutaneous injection, the livers were perfused with collagenase and dissociated. Fractionation of dissociated control and treated liver cells on Ficoll gradients yielded three cellular fractions. In preparations from carcinogen-exposed rats the percentage of hepatocytes excluding iron and positive for γ-glutamyl transpeptidase was always higher in the top (least dense) fraction than in the other lower fractions or the original population of dissociated hepatocytes. Moreover, the total number of hepatocytes in the top fraction increased progressively with the duration of feeding. These observations indicate that iron-excluding hepatocytes of enzyme-altered foci are less dense than other hepatocytes and can be enriched by gradient centrifugation. The progressive increase in the number of these altered liver cells with continued carcinogen exposure is consistent with a role for these cells in the development of liver tumors.     

Hepatocarcinogenic activity of N-butyl-N-(4-hydroxybutyl)nitrosamine in rats is not modified by sodium L-ascorbate

Male F344 and Wistar Shionogi (WS) rats were treated with 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) for 20 weeks and then killed at week 36 (experiment 1). Although reduction of body weight increase was found, no effects on liver weights were noted. Formalin-fixed and paraffin-embedded liver tissues from rats killed terminally were cut and stained for glutathione S-transferase placental form (GST-P) immunohistochemically. Marked elevation of quantitative values of small GST-P positive (GST-P+) foci were apparent in both strains of rat administered BBN. In experiment 2, both sexes of F344 rats were given 0.05% BBN in the drinking water for 4 weeks and then fed diet containing 0 or 5.0% sodium L-ascorbate (SA) for 32 weeks. No body and liver weight changes were evident in any group. Quantitative values for small GST-P+ foci were increased in both sexes of rats exposed to BBN but were not modified by additional SA treatment. Thus, it was confirmed that the selective bladder carcinogen BBN also acts as a liver carcinogen. These results, from the quantitative analysis of small GST-P+ foci as end point marker lesions, indicate that the liver tumor modifying potential of test chemicals can be evaluated in rats by using an initiation/promotion protocol for urinary bladder carcinogenesis.     

Comparison of adverse drug reaction profiles of two tacrolimus formulations in rats

Tacrobell^® (TB) is a generic tacrolimus which showed the comparable efficacy to original product, Prograf^® (PG) in renal transplantation, but toxicity between two drugs is unclear. The aim of this study was to compare the toxicity between these two formulations. TB and PG (0.5, 1 and 2?mg/kg/day) was administered to rats for 4 weeks. The rat survival rate, kidney, liver and pancreas injury was investigated. The survival rate was similar between TB- and PG-treated rats. TB and PG induced renal dysfunction in a dose-dependent manner. Compared to PG treatment in equal dose, TB treatment reduced urinary creatinine clearance in a less degree and renal interstitial fibrosis was comparable between two regimens. The r-glutamyl transpeptidase was aggravated by tacrolimus treatment, and this was not different between TB and PG treatment. In the intraperitoneal glucose tolerance test, a significant diabetogenic effect was observed in all tacrolimus treated-rats. The glucose tolerance of TB-treated rats was similar to those of PG-treated rats in each dose. The decrement in pancreatic β-cell mass by tacrolimus showed the dose-dependent response and it was comparable between TB and PG treatment. In conclusion, TB is similar to PG in terms of nephrotoxicity, hepatoxicity and diabetogenic effect.     

Comparison of adverse drug reaction profiles of two tacrolimus formulations in rats

Tacrobell(?) (TB) is a generic tacrolimus which showed the comparable efficacy to original product, Prograf(?) (PG) in renal transplantation, but toxicity between two drugs is unclear. The aim of this study was to compare the toxicity between these two formulations. TB and PG (0.5, 1 and 2?mg/kg/day) was administered to rats for 4 weeks. The rat survival rate, kidney, liver and pancreas injury was investigated. The survival rate was similar between TB- and PG-treated rats. TB and PG induced renal dysfunction in a dose-dependent manner. Compared to PG treatment in equal dose, TB treatment reduced urinary creatinine clearance in a less degree and renal interstitial fibrosis was comparable between two regimens. The r-glutamyl transpeptidase was aggravated by tacrolimus treatment, and this was not different between TB and PG treatment. In the intraperitoneal glucose tolerance test, a significant diabetogenic effect was observed in all tacrolimus treated-rats. The glucose tolerance of TB-treated rats was similar to those of PG-treated rats in each dose. The decrement in pancreatic β-cell mass by tacrolimus showed the dose-dependent response and it was comparable between TB and PG treatment. In conclusion, TB is similar to PG in terms of nephrotoxicity, hepatoxicity and diabetogenic effect.     

Liver tumor-promoting effect of beta-naphthoflavone, a strong CYP 1A1/2 inducer, and the relationship between CYP 1A1/2 induction and Cx32 decrease in its hepatocarcinogenesis in the rat

Interrelationships among induction of cytochrome P-450 (CYP) 1A1/2, decrease in connexin 32 (Cx32), and liver tumor-promoting activity by beta-naphthoflavone (BNF) in the promotion stage were examined in a 2-stage liver carcinogenesis model. A total of 20 male Fischer 344 rats were initiated with a single intraperitoneal injection of 150 mg/kg of diethylnitrosamine (DEN) or were given the saline vehicle alone. Starting 2 weeks later, they were fed a diet containing 2%, 1%, or 0% BNF for 6 weeks. All animals were subjected to a two-thirds partial hepatectomy at week 3 and were sacrificed at week 8. Absolute and relative liver weights were significantly increased in the DEN+BNF groups as compared to the DEN-alone group. Diffuse hepatocellular hypertrophy with cytoplasmic eosinophilia, sometimes accompanied by development of adenoma-like hepatic foci, was observed in the BNF-treated rats. Remarkable induction of cytochrome CYP 1A1/2 and significant increase in CYP 2E1 were noted in the DEN+BNF groups, and positive immunohistochemical staining for both was observed diffusely. The areas of Cx32-positive spots per hepatocyte in the centrilobular areas of livers of the BNF-treated rats were significantly decreased, but no changes were observed in periportal areas. The numbers and areas of foci positive for glutathione S-transferase placental form were increased in the BNF-treated groups. These results suggest that BNF is a liver tumor promoter that, unlike phenobarbital, does not induce CYP 2B1/2 isozymes, and there seems to be no direct relationship between CYP 1A1/2 induction and Cx32 reduction in BNF hepatocarcinogenesis.     

Effects of griseofulvin in medium-term liver carcinogenesis assay and peripheral blood micronucleus test in rat.

Published data have suggested a possible link between the tumor promoting activity and the aneugenic properties of griseofulvin. The present study was conducted to explore this relationship. Griseofulvin was evaluated both for its potential promoting activity in liver carcinogenesis in partially hepatectomized F344 male rats initiated by diethylnitrosamine and for its genotoxic potential in the peripheral blood micronucleus assay. Rats were treated daily with 2,000 mg/kg body weight by oral gavage for 12 weeks in the medium-term carcinogenesis bioassay. GST-P-positive foci (mean number and surface area) and altered cell foci were compared in the liver of rats treated with griseofulvin alone, diethylnitrosamine alone,and griseofulvin in addition to diethylnitrosamine by using immunohistochemical and histopathological evaluation, respectively. This evaluation allowed the conclusion that griseofulvin did not initiate the carcinogenic process but rather had a potential in the liver for tumor promoting activity. Griseofulvin was found to be negative in the rat peripheral blood micronucleus test when given at a daily oral dose of 2,000 mg/kg body weight for at least 3 weeks.     

Hepatocyte proliferation induced by a single dose of a peroxisome proliferator.

In compensatory hyperplasia after partial hepatectomy or liver cell injury, hepatocyte proliferation is triggered by coordinated actions of growth factor such as hepatocyte growth factor and transforming growth factor-alpha and -beta. Initiation of hepatocyte DNA synthesis is preceded by the activation of the set of early growth response genes mediated by enhanced nuclear factor-kappa B binding to DNA. Using an experimental model to induce hepatocyte DNA synthesis in vivo by a single dose of a peroxisome proliferator, which does not induce liver cell necrosis (direct hyperplasia), we investigated whether peroxisome proliferator-induced hepatocyte proliferation involved an induction of known growth factors, an activation of early growth response genes, and nuclear factor-kappa B. A single intragastric administration of 250 mg/kg BR931 (4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio-(N-beta-hydroxyethyl) acetamide) to male wistar rats induced a wave of hepatocyte DNA synthesis starting after 12 hours and peaking at approximately 24 to 36 hours. The response was dose dependent. The treatment also induced the expression of the mRNA for the peroxisomal bifunctional enzyme, one of the peroxisome-related fatty acid beta-oxidation enzymes. Pretreatment of rats with dexamethasone (2 mg/kg) inhibited both hepatocyte DNA synthesis and the induction of the peroxisomal bifunctional enzyme gene. Northern blot analyses of liver RNA during a period preceding the onset of DNA synthesis revealed no induction of hepatocyte growth factor, transforming growth factor-alpha, or tumor necrosis factor-alpha mRNAs. No induction of early growth response genes, liver regeneration factor-1, or c-myc was detected. Furthermore, gel mobility shift assays showed no enhanced nuclear factor-kappa B binding to its DNA consensus sequence after BR931 treatment, whereas control studies demonstrated a distinct increase in binding after partial hepatectomy or lead nitrate treatment. The results suggest that peroxisome-proliferator-induced hepatocyte proliferation may be triggered by signal transduction pathways different from those after partial hepatectomy and that the binding of peroxisome proliferators to their nuclear receptors may play a role in stimulation of DNA synthesis and peroxisome proliferation.     

The enhancing effect of ethanol on the development of glutatione S-transferase placental form-positive foci induced by diethylnitrosamine in F344 rat

The effects of ethyl alcohol and pig serum administration on the development of preneoplastic hepatic enzyme-altered foci were examined in an in vivo mid-term assay system. Rats were initially given a single dose (200 mg/Kg) intraperitoneal injection of diethylnitrosamine (DEN). Two weeks later, treatment was started with 10% ethanol + 10% sucrose solution, 10% sucrose solution, or tap water as drinking water for 6 weeks with or without intraperitoneal injection of porcine serum twice a week. All rats were subjected to a two-thirds partial hepatectomy at week 3. The modification potentials were evaluated by comparing the number and area per cm2 of glutathione S-transferase placental form-positive (GST-P+) foci in the liver of each group. As a result, ethanol significantly enhanced the development of GST-P+ foci. Unfortunately, the porcine serum injection produced no hepatic fibrosis and no significant alteration in GST-P+ foci.     

The pathologic response of the liver and thyroid of the rat to potassium prorenoate (SC-23992)

A 3-month dose range finding study in preparation for a 2-yr carcinogenicity study of potassium prorenoate (SC-23992), a steroid with an antihypertensive profile, is reported. The drug was administered by gavage once daily at doses of 10, 30, and 100 mg/kg/day to Charles River CD rats. Treatment was terminated at 13 weeks and 10 randomly selected animals from each treatment group were killed and necropsied. The remaining 10 animals in each dose group, including controls, were maintained for an additional 4 weeks, in order to investigate reversibility of changes, and then were killed and necropsied. Dose-related increases in thyroid-stimulating hormone (TSH) levels were observed in treated animals of both sexes during the dosing period and the changes were statistically significant and correlated with an increased thyroid weight in females at 13 weeks. Dose-related morphologic changes in the thyroid, observed by light and electron microscopy, were compatible with the effects of TSH stimulation. Liver weights, which increased, were dose-related. In females the increase was statistically significant at the high dose at 2, 4, and 13 weeks. In males it was significant at the high dose at 13 weeks. Microsomal enzyme levels were increased in a time- and dose-related manner with higher values in females than in males. The pattern of enzyme induction was of the type exemplified by pregnenolone- 16-alpha-carbonitrile. Morphologic changes in the liver showed centrilobular hepatocyte enlargement with smooth endoplasmic reticulum membrane proliferation confirmed by electron microscopy. All positive findings returned to normal after the 4-week treatment-free period. The relationship between the thyroid stimulation to liver enzyme induction is of interest. Evidence is presented here that in the presence of SC-23992, TSH stimulation and liver enzyme induction occurred. The possibility that the liver metabolism stimulates the thyroid T3, T4 elimination with secondary TSH activity is a possible explanation, but on the basis of existing information, direct action by SC-23992 on the thyroid cannot be excluded.     

Toxicity profiles in rats treated with tumorigenic and nontumorigenic triazole conazole fungicides: Propiconazole, triadimefon, and myclobutanil

Conazoles are a class of azole based fungicides used in agriculture and as pharmaceutical products. They have a common mode of antifungal action through inhibition of ergosterol biosynthesis. Some members of this class have been shown to be hepatotoxic and will induce mouse hepatocellular tumors and/or rat thyroid follicular cell tumors. The particular mode of toxic and tumorigenic action for these compounds is not known, however it has been proposed that triadimefon-induced rat thyroid tumors arise through the specific mechanism of increased TSH. The present study was designed to identify commonalities of effects across the different conazoles and to determine unique features of the tissue responses that suggest a toxicity pathway and a mode of action for the observed thyroid response for triadimefon. Male Wistar/Han rats were treated with triadimefon (100, 500, 1800 ppm), propiconazole (100, 500, 2500 ppm), or myclobutanil (100, 500, 2000 ppm) in feed for 4, 30, or 90 days. The rats were evaluated for clinical signs, body and liver weight, histopathology of thyroid and liver, hepatic metabolizing enzyme activity, and serum T3, T4, TSH, and cholesterol levels. There was a dose-dependent increase in liver weight but not body weight for all treatments. The indication of cytochrome induction, pentoxyresorufin O-dealkylation (PROD) activity, had a dose-related increase at all time points for all conazoles. Uridine diphopho-glucuronosyl transferase (UDPGT), the T4 metabolizing enzyme measured as glucuronidation of 1-naphthol, was induced to the same extent after 30 and 90 days for all three conazoles. Livers from all high dose treated rats had centrilobular hepatocyte hypertrophy after 4 days, while only triadimefon and propiconazole treated rats had hepatocyte hypertrophy after 30 days, and only triadimefon treated rats had hepatocyte hypertrophy after 90 days. Thyroid follicular cell hypertrophy, increased follicular cell proliferation, and colloid depletion were present only after 30 days in rats treated with the high dose of triadimefon. A dose-dependent decrease in T4 was present after 4 days with all 3 compounds but only the high doses of propiconazole and triadimefon produced decreased T4 after 30 days. T3 was decreased after high-dose triadimefon after 4 days and in a dose-dependent manner for all compounds after 30 days. Thyroid hormone levels did not differ from control values after 90 days and TSH was not increased in any exposure group. A unique pattern of toxic responses was not identified for each conazole and the hypothesized mode of action for triadimefon-induced thyroid gland tumors was not supported by the data.