Development Of Hepatic Tumors Research Articles

The role of metabolic activation in drug toxicity.

It is now well recognized that metabolic activation of drugs to reactive metabolites is an important mechanism in many drug-induced toxicities. This paper presents an overview of historical and current aspects of the role of metabolic activation in drug-induced cytotoxicity and concentrates on noncarcinogens. As discussed in the other articles in this special issue, the role of metabolic activation in toxicology was discovered by Drs. James A. Miller and Elizabeth C. Miller at the McArdle Institute, University of Wisconsin, while working on mechanisms of carcinogenicity of aminoazo dyes. In 1947 these investigators [I] reported that the livers of rats fed the carcinogen N,N-dimethyl-4-aminoazobenzene contained aminoazo dye firmly bound to the protein, and that these adducts preceded the development of hepatic tumors. In subsequent work the Millers showed that formation of the protein adducts was a result of metabolism of the azo dye, and that the presence of the azo dye-protein adducts correlated with the carcinogenicity of the aminoazodye under a variety of conditions. These and subsequent *Contributed in honor of Elizabeth C. Miller, Ph.D., and James A. Miller, Ph.D.

Rapid development of hepatic tumors in transforming growth factor alpha transgenic mice associated with increased cell proliferation in precancerous hepatocellular lesions initiated by N-nitrosodiethylamine and promoted by phenobarbital.

The carcinogenic and tumor-promoting effects of human transforming growth factor alpha (TGF-alpha) overexpression were examined in a two-stage chemical carcinogenesis protocol using TGF-alpha transgenic mouse line MT42. Male MT42 and CD-1 mice received a single i.p. injection of 5 mg N-nitrosodiethylamine (DEN)/kg body wt at 15 days of age, and were placed on a diet containing 0.05% of phenobarbital (PB) from 4 weeks of age for 35 weeks. DEN-, PB-treated and saline-injected animals in each strain were used as controls. A total of three sequential sacrifices (at 10, 23 and 37 experimental weeks) was performed. Hepatocellular carcinomas (HCCs) developed earlier at high incidence (100%) after 23 experimental weeks in MT42 mice receiving DEN/PB, while CD-1 mice had a 40% incidence of HCCs only after week 37. HCCs also developed in the DEN-initiated MT42 mice at 80% incidence after week 23, but no HCCs were observed in the DEN-initiated CD-1 mice. PB induced preneoplastic foci (67%), adenomas (33%) and HCCs (33%) after 37 weeks in MT42 mice, but no lesions were found in CD-1 mice. Thus, the carcinogenic response to DEN and/or PB was accelerated in the MT42 transgenic mice. Furthermore, PB promotion was observed from week 10 in MT42 mice and week 23 in CD-1 mice. Thus, the promoting effect of PB was also accelerated in the MT42 transgenic mice. Proliferating cell nuclear antigen (PCNA) labeling indices of hepatocellular foci and adenomas in DEN- or DEN/PB-treated MT42 mice were significantly higher than those of CD-1 mice. TGF-alpha expression determined by immunohistochemistry revealed higher levels in these lesions than in hepatocytes of surrounding parenchyma of MT42 transgenic mice. In conclusion, TGF-alpha transgenic mice clearly demonstrated enhanced sensitivity to the development of hepatocellular carcinoma in the DEN initiation and PB promotion regime, possibly through a mechanism of increased hepatocyte proliferation in precancerous lesions (foci and adenomas), driven by high expression of the mitogen TGF-alpha in these lesions.

Inhibition of aflatoxin B1-induced gamma-glutamyltranspeptidase positive (GGT+) hepatic preneoplastic foci and tumors by low protein diets: evidence that altered GGT+ foci indicate neoplastic potential.

Previous studies in this laboratory with young Fischer 344 male rats have shown that the post-initiation development of aflatoxin B1 (AFB1)-induced gamma-glutamyltranspeptidase positive (GGT+) hepatic foci was markedly inhibited by low protein feeding, even though the energy intake was greater. This dietary effect, however, did not necessarily apply to hepatic tumor development. Thus, the present investigation was undertaken to examine this dietary effect upon the development of hepatic tumors and, is so doing, to determine the correlation of foci development with tumor development. Following AFB1 dosing (15 daily doses of 0.3 mg/kg each), animals were fed diets containing 6, 14 or 22% casein (5.2, 12.2, 19.1% protein) for 6, 12, 40, 58 and 100 weeks. Foci at 12 weeks and tumors at 40, 58 and 100 weeks developed dose-dependently to protein intake. Foci development, tumor incidence, tumor size and the number of tumors per animal were markedly reduced while the time to tumor emergence was increased with low protein feeding. Non-hepatic tumor incidence also was lower in the animals fed the lowest protein diet. Foci development indices (foci number, per cent liver volume occupied) were highly correlated with tumor incidence at 58 and 100 weeks (r = 0.90-1.00). Tumor and foci inhibition occurred in spite of the greater energy intake.

Growth factors in liver development, regeneration and carcinogenesis

Liver growth during regeneration is controlled by several growth factors which may be involved in the triggering, progression and termination of hepatocyte replication. It is likely that liver regeneration involves both circulating factors and those produced in hepatic tissue during the growth response. TGFα is an autocrine stimulator of hepatocyte proliferation which increases transiently in replicating hepatocytes both in vivo and in vitro. Constitutive TGFα overexpression in young transgenic mice causes liver hypertrophy and enhanced proliferation that progress to hepatic tumor development in the great majority of animals after 12 months of age. In contrast, HGF is present in normal blood in humans and animals and plasma concentrations increase after partial hepatectomy, liver injury and fulminant hepatic failure. In liver tissue, levels of HGF and its mRNA correlate better with the extent of injury than with the degree of proliferative activity. The factor is produced by nonparenchymal cells and presumably acts on hepatocytes through paracrine or endocrine mechanisms. A transient increase of TGFβ1 in regenerating liver may promote the formation of extracellular matrix components and signal the end of hepatocyte proliferation. Prolonged overexpression of the factor in nonparenchymal cells causes liver fibrosis both in humans and experimental animals. The liver contains TGFβ1,2 and 3, all of which inhibit hepatocyte DNA synthesis. Their mRNAs increase in the regenerating liver but with very different kinetics. Despite the enormous progress achieved in understanding the mechanisms that regulate liver regeneration, it is not known whether HGF, TGFα and TGFβ interact with each other or with other factors or hormones during the growth process. Further, it remains to be established how the effect of these factors may relate to the sequential changes in proto-oncogene expression that occur after partial hepatectomy.

Overexpression of the Multidrug Resistance Gene mdr3 in Spontaneous and Chemically Induced Mouse Hepatocellular Carcinomas

Overexpression of a family of plasma membrane glycoproteins, known as P-glycoproteins, is commonly associated with multidrug resistance in animal cells. In rodents, three multidrug resistance (mdr or pgp) genes have been identified, but only two can confer the multidrug resistance phenotype upon transfection into animal cells. Using the RNase protection method, we demonstrated that the levels of three mdr gene transcripts differ among mouse tissues, confirming a previous report that the expression of these genes is tissue specific (J.M. Croop, M. Raymond, D. Huber, A. DeVault, R. J. Arceci, P. Gros, and D. E. Housman, Mol. Cell. Biol. 9:1346-1350, 1989). The levels of mdr transcripts were determined for mouse liver tumors spontaneously arising in both C3H/HeN and transgenic animals containing the hepatitis B virus envelope gene and for tumors induced by two different carcinogenic regimens in C57BL/6N and B6C3-F1 mice. The mdr3 gene was overexpressed in all 22 tumors tested. Our results demonstrate that overexpression of the mdr3 gene in mouse liver tumors does not require exposure of the animals to carcinogenic agents and suggest that its overexpression is associated with a general pathway of hepatic tumor development. The overexpression of the mdr3 gene, which is the homolog of human mdr1 gene, in hepatocellular carcinomas may be responsible for the poor response of these tumors to cancer chemotherapeutic agents.

Overexpression of the multidrug resistance gene mdr3 in spontaneous and chemically induced mouse hepatocellular carcinomas.

Overexpression of a family of plasma membrane glycoproteins, known as P-glycoproteins, is commonly associated with multidrug resistance in animal cells. In rodents, three multidrug resistance (mdr or pgp) genes have been identified, but only two can confer the multidrug resistance phenotype upon transfection into animal cells. Using the RNase protection method, we demonstrated that the levels of three mdr gene transcripts differ among mouse tissues, confirming a previous report that the expression of these genes is tissue specific (J.M. Croop, M. Raymond, D. Huber, A. DeVault, R. J. Arceci, P. Gros, and D. E. Housman, Mol. Cell. Biol. 9:1346-1350, 1989). The levels of mdr transcripts were determined for mouse liver tumors spontaneously arising in both C3H/HeN and transgenic animals containing the hepatitis B virus envelope gene and for tumors induced by two different carcinogenic regimens in C57BL/6N and B6C3-F1 mice. The mdr3 gene was overexpressed in all 22 tumors tested. Our results demonstrate that overexpression of the mdr3 gene in mouse liver tumors does not require exposure of the animals to carcinogenic agents and suggest that its overexpression is associated with a general pathway of hepatic tumor development. The overexpression of the mdr3 gene, which is the homolog of human mdr1 gene, in hepatocellular carcinomas may be responsible for the poor response of these tumors to cancer chemotherapeutic agents.

Increased expression of c-myc and c-H-ras in dichloroacetate and trichloroacetate-induced liver tumors in B6C3F1 mice

The expression of c-myc and c-H-ras in hyperplastic nodules and hepatocellular carcinomas induced in male B6C3F1 mice after chronic administration of dichloroacetate (DCA) and trichloroacetate (TCA) was studied using in situ hybridization. Expression of c-myc and c-H-ras mRNA was increased in both nodules and carcinomas relative to surrounding tissue and tissues obtained from control animals. Myc expression was similar in hyperplastic nodules and carcinomas induced by DCA, but was significantly higher in TCA-induced carcinomas than in hyperplastic nodules and carcinomas produced by DCA. In carcinomas from animals whose TCA treatment was suspended at 37 weeks, c-myc expression remained high relative to control and surrounding liver tissue at 52 weeks. In contrast, the expression of c-H-ras was consistently elevated in carcinomas from both treatments relative to hyperplastic nodules and non-tumor tissue. Within carcinomas from both treatments, focal areas could be located which expressed even higher levels of c-myc. This heterogeneity was not observed in carcinomas hybridized to c-H-ras-probes. These data suggest that elevated expression of c-H-ras and c-myc might play an important role in the development of hepatic tumors in B6C3F1 mice. Elevated expression of c-H-ras was closely associated with malignancy. Increased c-myc expression does not seem necessary for progression to the malignant state. On the other hand, the increased expression of c-myc appears related to the earlier progression of TCA-induced tumors to the malignant state.

Effect of dietary vitamin E on the development of altered hepatic foci and hepatic tumors induced by the peroxisome proliferator ciprofibrate

The purpose of this study was to determine the effect of the dietary antioxidant vitamin E on hepatocarcinogenesis by peroxisome proliferators which, it is hypothesized, induce tumors by increased production of hydrogen peroxide or other oxygen radicals. Rats were fed diets containing the peroxisome proliferator ciprofibrate and one of three concentrations (10, 50, or 500 ppm) of alpha-tocopheryl acetate for 6 months or 21 months. The incidence of hepatic tumors and the number and volume of gamma-glutamyl-transpeptidase-positive, ATPase-negative, glucose-6-phosphatase-negative, and glucose-6-phosphatase-positive foci were quantified. No tumors or altered hepatic foci were seen at 6 months, but at 21 months the incidence of hepatic tumors and the number and volume of altered hepatic foci were increased in rats fed higher levels of vitamin E. Indices of oxidative damage--concentrations of malonaldehyde, conjugated dienes, and lipid-soluble fluorescence products--were not affected or were lower in rats fed higher amounts of vitamin E; the enhancing effect of vitamin E on the development of altered hepatic foci and hepatic tumors, therefore, was not related to the induction of cellular oxidative damage. Hepatic peroxisomal fatty acid beta-oxidation and vitamin C concentrations were not affected by vitamin E, whereas the glutathione concentration was decreased in rats fed higher amounts of vitamin E. This study shows that increasing the vitamin E content of the diet enhances ciprofibrate-induced hepatocarcinogenesis, but the mechanism of this effect is unclear.

Dose-related carcinogenic effects of water-borne benzo[ a]pyrene on livers of two small fish species

Benzo[ a]pyrene (BaP) administered by water-borne exposures caused dose-related carcinogenic effects in livers of two small fish species, the Japanese medaka ( Oryzias latipes) and the guppy ( Poecilia reticulata). Medaka and guppies each were given two 6-h exposures. The first exposure was conducted on 6- to 10-day-old specimens. The second exposure was given 7 days later. The tests incorporated five treatment groups: (1) control, (2) carrier (dimethylformamide) control, (3) low BaP dose (not detectable-4 ppb), (4) intermediate BaP dose (about 8–47 ppb BaP), and (5) high BaP dose (200–270 ppb). Following the high-dose exposure, hepatocellular lesions classified as foci of cellular alteration (altered foci), adenomas, and hepatocellular carcinomas occurred in both species. In medaka, the lesions appeared to develop sequentially with the appearance of altered foci followed by adenomas and then hepatocellular carcinomas. Most lesions in guppies, however, were classified as altered foci although a few adenomas occurred in the early (24-week) sample and hepatocellular carcinomas occurred in the late (52-week) sample. When total lesions were combined, medaka had an 11% incidence at 24 weeks after the initial exposure and 36% incidence at 36 weeks. In guppies, 8% had liver lesions at 24 weeks 19% at 36 weeks, and 20% at 52 weeks. A single extrahepatic neoplasm, a capillary hemangioma in a gill filament, occurred in a medaka from the 36-week high-dose sample. The results suggest that the medaka and guppy are capable of metabolizing water-borne BaP to carcinogenic metabolites which initiate hepatic tumor development.

Hepatocellular carcinoma in type I glycogen storage disease

Patients suffering from Type I glycogen storage disease frequently develop hepatic tumors. Some of these were classified as carcinoma, with the majority of tumors representing benign adenomata. However, no evidence exists of malignant transformation of adenomata in these patients. Here, we describe the occurrence of a hepatocellular carcinoma in the adenomata-bearing liver of the elder of two sisters suffering from Type I glycogen storage disease at the age of 20 years, 6 years after the diagnosis had been made. Surprisingly, alpha-fetoprotein levels were normal throughout the entire course of this patient, whereas the younger sister had elevated levels despite the absence of malignant lesions. Thus, the clinical significance of alpha-fetoprotein remains unclear in both cases. Nocturnal feeding, although performed continuously over the 6 years after the diagnosis, had obviously failed to prevent the development of hepatic tumors in both patients.

Prolactin as a mammalian mitogen and tumor promoter

Cellular proliferation and differentiation of the mammalian mammary gland requires a medley of hormones including the anterior pituitary hormone, PRL. Recent evidence extends the role of PRL as a mammalian mitogen to cells in several physiological systems not directly involved in reproductive functions, such as liver and lymphocytes. PRL administration induces biochemical markers expressed during the G 1 phase of cell cycle and activates DNA synthesis in rat liver. Chronic PRL treatment causes hepatomegaly, reflecting its stimulation of the proliferative process. In vitro, a lactogen-dependent cell line, the Nb2 rat node lymphoma cell, serves as a useful paradigm to study PRL action on mitogenesis. These cells, when cultured in the presence of lactogens, proliferate in a dose-dependent manner. The effects of various pharmacological agents on discrete phases of the cell cycle may be readily assessed in these cells since PRL-stimulated entry into cycle is signalled by an elevation of ODC activity at 6 hr and entry into S-phase at 6–12 hr. The parallel effects of phorbol ester tumor promoters and PRL on cell cycle progression in Nb2 lymphoma cells and in hepatic proliferation suggest that PRL may likewise mediate proliferation in aberrant growth conditions such as neoplasia. The data presented support the hypothesis that PRL is capable of promoting hepatocarcinogenesis. Its chronic administration after a hepatic initiating agent stimulated the development of histochemical and biochemical markers characteristic of preneoplasia. Further, the effect of PRL was comparable to that of the hepatocarcinogen when either was administered alone. Thus, hyperprolactinemia may serve to promote the development of hepatic tumors. Phorbol esters are thought to promote tumorigenesis by directly activating PKC. In the Nb2 lymphoma cell model, tumor promoting phorbol esters mimic the effects of PRL. Similarily, PRL-stimulated enzyme induction in liver is mirrored by phorbol ester treatment, and inhibitors of PKC block PRL-stimulated mitogenesis in Nb2 cells. Further, PRL or TPA administration to rats causes translocation of PKC activity from the hepatic cytosol to the membrane fraction, reflecting kinase activation. Therefore, PRL activation of PKC appears to be a physiological phenomenon of general significance, occurring as the result of lactogen receptor stimulation and serving to transmit intracellular signals linked to the regulation of mitogenesis. Further study is required to more fully define the scope of PRL-mediated mitogenic actions as well as its effects on the expression of differentiated products in tissues and cells.

Expression and regulation of glycogen phosphorylase in preneoplastic and neoplastic hepatic lesions in rats.

Glycogen phosphorylase (PHO) was demonstrated immunocytochemically and enzyme histochemically in cryostat sections of liver from rats treated for 7 weeks with N-nitrosomorpholine (120 mg/l and 200 mg/l drinking water) and from untreated controls. The activity and distribution of PHO protein were studied in normal liver and correlated with morphologically defined stages of hepatic tumour development. In normal liver the amount of enzyme protein, as visualized by the immunoperoxidase method using antibodies against phosphorylase, showed some heterogeneity within the liver lobule. The intralobular and intracellular distribution of PHO protein was the same as that of glycogen, namely coarse and granular in periportal hepatocytes and very fine in perivenular cells. In glycogen storage foci the amount of PHO protein was increased. In contrast, PHO activity was generally decreased. In other preneoplastic and neoplastic lesions such as mixed cell foci, neoplastic nodules and hepatocellular carcinomas, PHO protein was increased in all glycogen-loaded cells while PHO activity was reduced. In all glycogen-poor and basophilic cells, both PHO protein and PHO activity were decreased or absent. It was concluded that the decrease in PHO activity in glycogen storage foci was not the direct consequence of genetic changes leading to a loss in enzyme protein but was due to a defect in the cascade of phosphorylation processes resulting in active PHO. Alteration in gene expression leading to a loss of PHO protein was a late event in the process of hepatocarcinogenesis.

Nuclear magnetic resonance spectroscopy and imaging in the study of experimental liver diseases.

We are investigating potential noninvasive new strategies for the assessment of liver injury, steatosis, and hepatic tumor development. These techniques employ nuclear magnetic resonance (NMR) imaging and spectroscopy. Accordingly, several experimental animal models of liver injury and steatosis produced in rats by ethanol, azaserine, L-ethionine, carbon tetrachloride, and D-galactosamine. Ethanol and L-ethionine induce acute steatosis without necrosis, whereas azaserine, carbon tetrachloride, and D-galactosamine are known to produce steatosis with varying degrees of hepatic necrosis. Triglyceride content and protein spin relaxation times were measured. T1 values were analyzed by using an inversion recovery technique at eight different tau values (20 msec to 2.50 sec) and T2 by Carr-Purcell-Meibloom-Gill pulse sequences with 10 spin echoes (4-40 msec). We also performed NMR imaging studies on controls and ethanol-induced steatosis using a 60-MHz Technicare 8-cm bore superconducting system. Results of these experiments indicate that varying degrees of steatosis produce striking changes in T2 without inducing changes in T1, whereas necrosis superimposed on steatosis produces T1 changes as well. Thus, these NMR spectroscopy and imaging studies demonstrated that steatosis may be clearly defined in vitro and in vivo.

Carcinogenicity of <italic>o</italic>-Ethoxybenzamide in (C57BL/6N × C3H/HeN)F<sub>1</sub> Mice<xref ref-type="fn" rid="FN2">2</xref>

The carcinogenicity of o-ethoxybenzamide (CAS: 938-73-8), which is also called ethenzamide and which is widely used as an antipyretic anodyne in Japan, was examined in 298 (C57BL/6N X C3H/HeN)F1 mice. Groups of males and females were fed a diet containing 0 (control), 0.4, or 1.2% o-ethoxybenzamide for 96 weeks and sacrificed at the 100th week. Among the male mice fed the higher dose of the drug, the total incidence of liver cell tumors was 68%, with 18% of the mice developing hepatocellular carcinomas; both yields were significantly higher than those in the controls. In o-ethoxybenzamide-treated male mice the multiplicities of the hepatic cell tumors were also significantly higher than the multiplicity of the hepatic tumor in male control mice. A dose-response relationship with regard to both incidence and multiplicities of hepatic cell tumors in male mice was observed. In female mice fed o-ethoxybenzamide the incidence and multiplicities of the liver cell tumors were increased compared to those of the controls, but statistical significance was observed only in the multiplicity of tumors in mice given the lower dose. In both sexes hepatic cell tumors developed earlier than in the controls. These results show that o-ethoxybenzamide enhances the development of hepatic cell tumors in male (C57BL/6N X C3H/HeN)F1 mice.

<italic>N</italic>-Nitroso-<italic>N</italic>-methylurea Initiation in Multiple Tissues for Organ-Specific Tumor Promotion in Rats by Phenobarbital<xref ref-type="fn" rid="FN2">2</xref>

Effects of phenobarbital [(PB) CAS: 50-06-6], a systemic tumor promoter, on carcinogenesis initiated by the broad-spectrum carcinogen N-nitroso-N-methylurea [(NMU) CAS: 684-93-5] were investigated in F344/NCr rats. Single and divided doses of NMU were evaluated for this purpose in 4-week-old rats of both sexes. Rats received iv injections of either 0.2 mmol NMU/kg (body wt) once or 0.05 mmol NMU/kg (body wt) for 4 weeks (1 injection/wk), followed by or concurrently with PB (0.05% in drinking water) that was continued until the termination of the experiment. Half the rats were killed at 52 weeks and survivors at 80 weeks. At 52 weeks, PB given subsequent to NMU or concurrently with divided doses of NMU significantly enhanced the incidence of thyroid follicular tumors only in male rats. This sex difference in thyroid tumorigenesis was somewhat less pronounced in animals killed at 80 weeks. Only 1 liver cell adenoma occurred in males and none in females given NMU alone. PB given concurrently with divided doses of NMU enhanced the yield of hepatocellular foci/cm2 but had no significant effect on hepatic tumor development. Subsequent exposure to PB, however, significantly promoted hepatocarcinogenesis in rats of both sexes given NMU in divided doses; 50% of males and 40% of females given NMU (0.05 mmol/kg, administered four times) followed by PB had hepatocellular adenomas and carcinomas by 80 weeks. PB did not affect the incidence of any other kind of neoplasms seen in NMU-initiated or control rats. These lesions included squamous cell neoplasms of the skin, oropharynx, and forestomach; nonsquamous epithelial tumors of mammary gland, pituitary body, intestinal mucosa, and urinary bladder; tumors of the central and peripheral nervous system; and mesenchymal tumors of the kidney. A sequence of multiple low doses of NMU appeared to be a convenient and useful systemic, multitissue, tumor-initiation regimen for systematic investigation of organ-specific tumor promotion in rats.

Sex Difference in the Susceptibility of Rats to the Development of Porphyria and Hepatic Tumours caused by Hexachlorobenzene

Sex Difference in the Susceptibility of Rats to the Development of Porphyria and Hepatic Tumours caused by Hexachlorobenzene

Carcinogenicity of Dipyrone in (C57BL/6 × C3H)F1 Mice2

The carcinogenicity of dipyrone (sulpyrin)--[(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4 -yl) methylamino]methanesulfonic acid sodium salt monohydrate--which is widely used as an antipyretic anodyne in Japan and in some European countries, was examined in 314 (C57BL/6 X C3H)F1 mice. Male animals were given 0.5% (group I-a) or 0.125% (group I-b) dipyrone in their drinking water for 78 weeks, and female animals were given 1.0% (group II-a) or 0.25% (group II-b) dipyrone in their drinking water for 78 weeks; both males and females were observed for 86 weeks. Twenty-seven of 48 (56%) group I-a animals and 36 of 44 (82%) group II-a animals developed hepatic tumors, and the tumors in group II-a mice developed earlier than those in the control animals. The tumor incidences were significantly higher than those of 8 of 44 (18%) and 3 of 51 (6%) in the respective control groups. The multiplicity of the hepatic tumors was also significantly increased in groups I-a, I-b, and II-a. Hepatic adenoma incidence was related to the dose of dipyrone in the males. These results show that dipyrone enhances the development of hepatic tumors in mice.

Synergism of Diethylstilbestrol and Other Carcinogens in Concurrent Development of Hepatic, Mammary, and Pituitary Tumors in Castrated Male Rats<xref ref-type="fn" rid="FN2">2</xref>

Castrated male WF rats, given implants of pellets containing 5.0 mg diethylstilbestrol (DES), were given N-butyl-N-nitrosourea (NBU) in small amounts, which alone produced no mammary tumors in intact female rats. Treatment resulted in the high yield of hepatic tumors (HT), mammary tumors (MT), and pituitary tumors (PT) concurrently in each rat. If animals were further treated with prolactin, the development of HT and MT was accelerated, whereas that of PT was suppressed. None of the intact or castrated rats receiving NBU and/or prolactin developed tumors in any tissues if DES treatment was omitted. Exposure of male rats, preconditioned similarly to NBU treatment, to 200 rads of 14.1-MeV fast-neutron radiation also elicited HT, MT, and PT with an efficiency comparable to that of NBU-treated rats. These findings indicate that DES played an essential role in the whole carcinogenic process in each tissue and that castrated male rats, if conditioned properly with estrogens, are useful for the study of the carcinogenesis mechanism in these tissues.

Benign hepatic tumors and oral contraceptive pills

In order to consider possible environmental factors related to the development of benign hepatic tumors, all reports of this disorder in the case records of five different hospitals in Rochester, New York, during the past 10 years were reviewed. Seven patients with benign hepatic tumors of the liver and two with peliosis hepatis were identified. Among the seven with a benign hepatic tumor, four were women currently receiving oral contraceptives; one had been receiving this medication in the past, and two had no history of exposure to any steroid whatsoever. The two patients with peliosis hepatis were receiving long-term androgenic anabolic steroids. Dilated, thin-walled vessels and vascular spaces were a more prominent feature of the tumor seen in four patients receiving oral contraceptive pills. It is emphasized in this report that benign hepatic tumors do occur in men and in patients with cirrhotic liver without the use of any kind of steroids.

Inhibiting Effect of Chlorpromazine on the Experimental Production of Liver Cancer

RECENTLY, Griffin, Rinfret and Corsigilia1 reported that development of hepatic tumours in rats fed on a diet containing 0.06 per cent 3′-methyl-4-dimethyl-aminoazobenzene may be effectively inhibited by hypophysectomy. Chlorpromazine is a phenothiazine derivative, which is used medicinally as a potent depressant for the interbrain. Aron, Guelfi and Voisin2 reported an atonic effect of this drug on the sensibility of the pituitary gland induced by stress.