Cell Proliferation In Rat Liver Research Articles

The role of ZNF143 overexpression in rat liver cell proliferation

BackgroundZinc finger protein 143(ZNF143), a member of the Krüppel C2H2-type zinc finger protein family, is strongly associated with cell cycle regulation and cancer development. A recent study suggested that ZNF143 plays as a transcriptional activator that promotes hepatocellular cancer (HCC) cell proliferation and cell cycle transition. However, the exact biological role of ZNF143 in liver regeneration and normal liver cell proliferation has not yet been investigated.MethodsIn our study, we constructed a stable rat liver cell line (BRL-3A) overexpressing ZNF143 and then integrated RNA-seq and Cleavage Under Targets and Tagmentation (CUT&Tag) data to identify the mechanism underlying differential gene expression.ResultsOur results show that ZNF143 expression is upregulated during the proliferation phase of liver regeneration after 2/3 partial hepatectomy (PH). The cell counting kit-8 (CCK-8) assay, EdU staining and RNA-seq data analyses revealed that ZNF143 overexpression (OE) significantly inhibited BRL-3A cell proliferation and cell cycle progression. We then performed CUT&Tag assays and found that approximately 10% of ZNF143-binding sites (BSs) were significantly changed genome-wide by ZNF143 OE. However, CCCTC-binding factor (CTCF) binding to chromatin was not affected. Interestingly, the integration analysis of RNA-seq and CUT&Tag data showed that some of genes affected by ZNF143 differential BSs are in the center of each gene regulation module. Gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses indicated that these genes are critical in the maintenance of cell identity.ConclusionThese results indicated that the expression level of ZNF143 in the liver is important for the maintenance of cell identity. ZNF143 plays different roles in HCC and normal liver cells and may be considered as a potential therapeutic target in liver disease.

HUCB-MSC derived exosomal miR-124 promotes rat liver regeneration after partial hepatectomy via downregulating Foxg1

Liver regeneration after partial hepatectomy (PH) is a complex and well-orchestrated process involving multiple factors such as cytokines, growth factors, and signaling pathways. MicroRNAs (miRNAs) participate in various biological processes including liver regeneration after PH. In the current study, we investigated the expression and function of human umbilical cord blood mesenchymal stem cell (hUCB-MSC) derived exosomal miRNAs on liver regeneration using a rat PH model. We found that hUCB-MSC derived exosomes promoted rat liver regeneration and ameliorated liver injury after PH. MicroRNA microarray was performed to identify the differentially expressed miRNAs in hUCB-MSC derived exosomes involving in liver regeneration after PH. We demonstrated that hUCB-MSC derived exosomal miR-124 could promote liver regeneration and prevent against liver injury after PH in rats. Inhibition of miR-124 abrogated the protective role of hUCB-MSC derived exosome in rat liver regeneration after PH. In addition, we identified that transcription factor Foxg1 was a direct target of miR-124 and miR-124 promoted rat liver cell proliferation via suppressing Foxg1 expression. Furthermore, we demonstrated that hUCB-MSC derived exosomal miR-124 enhanced liver regeneration via inhibiting Foxg1 in rats after PH. In summary, our findings suggest that hUCB-MSC-derived exosomal miR-124 could promote rat liver regeneration after PH via downregulating Foxg1.

PLCG2 promotes hepatocyte proliferation in vitro via NF-κB and ERK pathway by targeting bcl2, myc and ccnd1

Phospholipase Cγ2 (PLCG2) has been implicated in the regulation of cell proliferation, transformation, and tumor growth. In this study, we investigate the mechanism of PLCG2 action using a short interference RNA (siRNA) method. The effects of PLCG2 on rat liver BRL-3A cells treated siRNA were studied by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT assay), bromodeoxyuridine (BrdU) labelling assay, flow cytometry method (FCM), quantitative real-time polymerase chain reaction (qRT-PCR) and western blot. The results showed when PLCG2 was reduced, cell vitality and proliferation rate were significantly decreased (p < .05 vs. control). FCM analysis showed that the number of cell division phase (G2 + M) was declined (p < .05 vs. control). RT-PCR and western blot revealed that the expression of signalling related genes NF-κB, FOS, JUN and ELK, target genes BCL2, CCNB1 and CCND1 were remarkably down-regulated in cells treated with PLCG2 siRNAs. Based on these results, we conclude PLCG2 plays an important role in rat liver cell proliferation via ERK and NF-κB pathway by regulating the expression of BCl2, MYC and CCND1.

Tri-iodothyronine induces hepatocyte proliferation by protein kinase a-dependent β-catenin activation in rodents

Thyroid hormone (T3), like many other ligands of the steroid/thyroid hormone nuclear receptor superfamily, is a strong inducer of liver cell proliferation in rats and mice. However, the molecular basis of its mitogenic activity, which is currently unknown, must be elucidated if its use in hepatic regenerative medicine is to be considered. F-344 rats or C57BL/6 mice were fed a diet containing T3 for 2-7 days. In rats, administration of T3 led to an increased cytoplasmic stabilization and nuclear translocation of β-catenin in pericentral hepatocytes with a concomitant increase in cyclin-D1 expression. T3 administration to wild-type (WT) mice resulted in increased hepatocyte proliferation; however, no mitogenic response in hepatocytes to T3 was evident in the hepatocyte-specific β-catenin knockout mice (KO). In fact, T3 induced β-catenin-TCF4 reporter activity both in vitro and in vivo. Livers from T3-treated mice demonstrated no changes in Ctnnb1 expression, activity of glycogen synthase kinase-3β, known to phosphorylate and eventually promote β-catenin degradation, or E-cadherin-β-catenin association. However, T3 treatment increased β-catenin phosphorylation at Ser675, an event downstream of protein kinase A (PKA). Administration of PKA inhibitor during T3 treatment of mice and rats as well as in cell culture abrogated Ser675-β-catenin and simultaneously decreased cyclin-D1 expression to block hepatocyte proliferation. We have identified T3-induced hepatocyte mitogenic response to be mediated by PKA-dependent β-catenin activation. Thus, T3 may be of therapeutic relevance to stimulate β-catenin signaling to in turn induce regeneration in selected cases of hepatic insufficiency.

520 Effect of selenium on rat liver cell proliferation after partial hepatectomy

Weekly cutaneous application of N-nitrosobis (2-oxopropyl)amine (BOP) at a dose of 2 mg/application to the neck area resulted in the induction of local papillomas and carcinomas in 80% of Syrian hamsters as early as 19 weeks post-treatment. In addition, a few tumors of internal organs (predominantly in the liver) were also found. N-Nitroso(2-hydroxypropyl) (2-oxopropyl)amine (HPOP), a common metabolite of BOP and BHP, was also found to be an epidermal carcinogen at a dose of 3.8 mg/application. N-Nitrosobis(2-hydroxypropyl)amine (BHP), however, failed to induce any epidermal lesions, when applied similarly at a much higher dose level (50 mg/animal/week). In contrast to BOP and HPOP, BHP induced a high incidence of tumors in internal organs, especially pancreatic cancer, which was the only induced tumor in 5 animals.Skin absorption studies demonstrated that BHP, but not BOP is rapidly absorbed and was detectable in the blood in concentrations of up to 5.5 μg/ml as early as 15 min after carcinogen administration. The possible reasons for the differing effects of BHP and BOP upon hamster skin are discussed.

The Thyroid Hormone Receptor-β Agonist GC-1 Induces Cell Proliferation in Rat Liver and Pancreas

Thyroid hormones regulate cell growth, cell differentiation, and metabolic functions via interaction with the thyroid hormone nuclear receptors (TRs). Recently, a small class of halogen-free high-affinity thyroid hormone agonists has been developed that are highly selective for the TRbeta subtype. Because of the selective hyperthyroidism generated by one of these agonists, GC-1, this compound has the potential to be developed as a new therapeutic agent for the treatment of a variety of metabolic disturbances, including lipid disorders and obesity; thus, it becomes important to determine whether GC-1 has other unknown effects on potential target organs. The purpose of this study was to investigate the effect of GC-1 on cell proliferation in rat liver and pancreas. Rats treated with GC-1 (50 or 100 mug/100 g body weight) were killed at different time points. Hepatic and pancreatic cell proliferation was monitored by immunohistochemical determination of bromodeoxyuridine incorporation. The expression of cell cycle-related genes was analyzed by Northern and Western analysis. The results show that GC-1 strongly stimulates rat hepatocyte proliferation in the absence of tissue injury. Although GC-1-induced hepatocyte proliferation was associated with a rapid increase in cyclin D1 mRNA levels, no change in the expression of c-jun and c-fos was observed. GC-1 also induced massive pancreatic cell proliferation. The results indicate that the TRbeta-selective agonist GC-1 is a strong mitogen for hepatocytes and pancreatic acinar cells. Furthermore, they suggest that the TRbeta receptor is the mediator for the mitogenic activity of thyroid hormone and other thyromimetics.

Time Course of Cell Proliferation in Rat Liver in the Early Postnatal Ontogeny and Role of Epidermal Growth Factor in Organization of Proliferative Regimen

Circadian rhythm of DNA synthesis, mitotic activity, and duration of mitosis in rat liver were studied on days 3, 7, and 12 of life. Age-associated differences in the rhythmic parameters of these characteristics were detected. Epidermal growth factor plays an important role in the formation of cell proliferation rhythm in the early postnatal ontogeny and in the formation of proliferative hepatocyte pool.

Intraperitoneal injection ofd-galactosamine provides a potent cell proliferation stimulus for the detection of initiation activities of chemicals in rat liver

In an in vivo 5-week initiation assay model, chemical hepatectomy by hepato-toxicant administration was utilized as a cell proliferation stimulus as an alternative to the two-thirds partial hepatectomy. The study investigated the effect of an intraperitoneal (i.p.) injection of D-galactosamine (D-gal) for this purpose in a medium-term liver bioassay, with a further focus on cell proliferation kinetics and cytochrome P450 (CYP) expression. In experiment I, cell proliferation in rat liver after a single administration of D-gal (700 mg kg(-1), i.p.) was analysed by the bromodeoxyuridine (BrdU) labeling method, and CYP isozymes were quantified by immunoblotting. In experiment II, the induction of glutathione S-transferase placental form (GST-P) positive foci by 1,2-dimethylhydrazine (DMH) was evaluated in a modified in vivo 5-week initiation assay model. At 84 hours after single administration of d-gal (i.p.) the BrdU index was markedly elevated (27.5% +/- 9.5%). Although CYP 2E1 and 1A2 apoprotein contents decreased transiently to less than 20% of the control level, subsequently they recovered to 60% and 40% of the control level, respectively, at 84 hours. Induction of GST-P positive foci in the group given DMH at 84 hours after a single administration of d-gal was significantly greater than in the control group, correlating with the kinetics of cell proliferation. In conclusion, the sensitivity of the present initiation assay using D-gal i.p. is high, so that D-gal i.p. can be considered an effective cell proliferation stimulus.

Diurnal dynamics of cell proliferation in rat liver during early postnatal ontogeny and effect of epidermal growth factor on hepatocyte proliferative activity

Circadian rhythms of DNA synthesis, mitotic activity, and duration of mitosis in rat liver were studied on postnatal days 3, 7, and 12. Some age-related peculiarities of these rhythms were revealed. Epidermal growth factor was found to play an important role in the formation of cell proliferation rhythm during the early postnatal ontogeny and in the regulation of the pool of proliferating hepatocytes.

823 The CDK2 inhibitor CYC202 (R-roscovitine) inhibits DNA synthesis and cell proliferation in rat liver after partial hepatectomy

Kinesin and ncd (non-claret disjunctional) are microtubule associated motor proteins which share several structural features: both motors are dimers; each monomer is composed of a stalk region, a cargo binding domain and a motor domain; the motor domains have ∼41% sequence identity. Despite these similarities the two motors have strikingly different movement properties: kinesin is a plus-end directed molecular motor, while ncd is minus-end directed. Here we compare the structure and the microtubule-binding properties of these oppositely directed molecular motors. We determined the three-dimensional structure of tubulin sheets decorated with the motor domains of either kinesin or ncd to a resolution of <20 Å by negative stain electron microscopy and tilt series reconstruction. Comparisons with a control structure of tubulin alone revealed that in both cases the motor domain binds to the outer crest of a single protofilament making contacts with both α and β tubulin. Despite their opposite directionality, the geometry of attachment of the motor domain to the protofilament in the presence of AMP-PNP is very similar for both motors. These data rule out models for directionality which have the motors binding in an opposite orientation to the microtubules. Binding of the ncd as well as the kinesin motor domain appears to induce conformational changes in tubulin. This observation suggests an active role of tubulin in motor movement and/or in the determination of directionality.

Brain stem GABA receptor functional regulation during rat liver cell proliferation.

GABAergic alterations in brain stem during compensatory hyperplasia after partial hepatectomy (PH), lead nitrate (LN)-induced direct hyperplasia, and N-nitrosodiethylamine (NDEA)-induced neoplasia in liver were investigated. GABA content decreased in brain stem of PH- and NDEA-treated rats while it increased in LN-treated rats. GABA(A) receptor number and affinity in brain stem membrane preparations of rats showed a significant decrease in PH- and NDEA-treated rats. The GABA(B) receptor number increased in PH- and NDEA-treated rats with an increase in affinity. The results of the present study indicate that liver cell proliferation is influencing the brain stem GABAergic neurotransmission and these changes regulate the hepatic proliferation through the sympathetic stimulation.

Hepatic GABA A receptor functional regulation during rat liver cell proliferation

Gamma aminobutyric acid (GABA A) receptor functional status was analysed in partial hepatectomised (PH), lead nitrate (LN) induced hyperplastic and N-nitrosodiethylamine (NDEA) treated neoplastic rat livers during peak DNA synthesis. The high-affinity [ 3H]GABA binding significantly decreased in PH and NDEA rats and the receptor affinity decreased in NDEA and increased in LN rats compared with control. In NDEA, displacement analysis of [ 3H]GABA with muscimol showed loss of low-affinity site and a shift of high-affinity site towards low-affinity. The affinity sites shifted towards high-affinity in LN rats. The number of low-affinity [ 3H]bicuculline receptors decreased significantly in NDEA and PH whereas it increased in LN rats. GABA A receptor agonist, muscimol, dose dependently inhibited epidermal growth factor (EGF) induced DNA synthesis and enhanced the transforming growth factor β1 (TGFβ1) mediated DNA synthesis suppression in primary hepatocyte cultures. Our results suggest that GABA A receptor act as an inhibitory signal for hepatic cell proliferation.

Expression of inhibin betaA, betaB and follistatin mRNAs in the carbon tetrachloride induced rat liver regeneration model.

Follistatin (FS, an activin-binding protein) and activin A (homodimer of inhibin betaA chain) promote and inhibit cell proliferation in rat liver, respectively. The roles of activin AB (heterodimer of inhibin betaA and betaB) and activin B (homodimer of inhibin betaB) in rat liver have not been elucidated yet. In this study, we examined, by reverse-transcriptase polymerase chain reaction (RT-PCR) analysis, whether the levels of FS, inhibin betaA and betaB mRNAs change in the carbon tetrachloride induced rat liver regeneration model. The analysis was made in an hour-by-hour manner during the early stage of liver injury. There are 2 types of FS mRNA, FS-288 and FS-315, and the levels of both had begun to increase at 3 h, were maximal at 6 h, remained constant up to 12 h, and thereafter gradually decreased. The inhibin betaA mRNA had started to decline at 3 h, reached its lowest level at 6 h, partly returned at 12 h, and remained constant up to 48 h. The inhibin betaB mRNA level had begun to increase at 1 h, was maximal at 3 h, remained constant up to 24 h, and returned to the original level at 48 h. These results indicate that FS and activin A may act reciprocally in liver regeneration, and also suggest that activin AB and B may play roles in liver regeneration that differ from that of activin A.

Differences in kinetics of induction and reversibility of TCDD-induced changes in cell proliferation and CYP1A1 expression in female Sprague-Dawley rat liver.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent tumor promoter in two-stage initiation-promotion models and induces cell proliferation and development of enzyme-altered hepatic foci. It is believed that increased cell proliferation is a necessary step in carcinogenesis. Therefore, the analysis of the effect of TCDD on cell proliferation in rat liver may aid in the understanding of the mechanism of hepatocarcinogenesis induced by TCDD. The aim of this study was to investigate the time course and reversibility of cell proliferation in non-initiated and diethylnitrosamine-initiated female rats exposed biweekly to a daily averaged dose of 125 ng TCDD/kg/day for up to 60 weeks. In addition we evaluated the suitability of different dose metrics for the evaluation of TCDD-induced changes in cell proliferation and CYP1A1 enzyme induction. Cell proliferation was measured as the incorporation of 5-bromo-2'-deoxyuridine (BrdU) into hepatocytes undergoing replicative DNA synthesis. Mean BrdU labeling indices in TCDD-treated animals were not increased over controls after 14 weeks exposure, but were increased 8- and 2-fold after 30 and 60 weeks' treatment respectively, despite similar liver levels of TCDD at all these times (23-30 p.p.b.). In comparison, CYP1A1 activity, as measured by ethoxyresorufin deethylase activity, was significantly induced at all times points analyzed. Sixteen weeks following cessation of TCDD treatment, labeling indices were still significantly elevated over controls, but after 30 weeks of withdrawal, labeling indices were no different from controls, indicating that TCDD-induced changes in cell proliferation were reversible. Dosimetric analysis indicated that rat liver tissue burden was suitable for prediction of CYP1A1 expression but not cell proliferation and that the area under the curve was unsuitable for prediction of both TCDD-induced changes in CYP1A1 expression and cell proliferation.

Comparison of Dose–Response Relationships for Induction of Lipid Metabolizing and Growth Regulatory Genes by Peroxisome Proliferators in Rat Liver

The regulation of gene expression via the peroxisome proliferator-activated receptor (PPAR) is believed to be critical in the effects of peroxisome proliferators on lipid metabolism and possibly in hepatocarcinogenesis. The involvement of PPAR in the peroxisome proliferator-mediated induction of fatty acid metabolizing genes such as acyl-CoA oxidase (ACO), fatty acid-binding protein (FABP), and cytochrome P450IVA1 (CYP4A1) has been clearly demonstrated. However, the induction by peroxisome proliferators of important growth regulatory genes such asc-mychas not been investigated extensively. In these studies we examined the dose–response relationships for the induction of mRNA for the PPAR-regulated and lipid metabolizing genesACO, FABP,andCYP4A1and compared them to the immediate early genec-myc.Liver mRNA from rats fed various amounts of the peroxisome proliferator Wy14,643 for 13 weeks was utilized. The lipid metabolism and growth regulatory genes were induced by subchronic administration of Wy14,643 but to varying degrees and with different sensitivities. The lowest dose that resulted in a significant change in ACO and FABP expression was 10 ppm. The mRNA for CYP4A1 and c-myc was significantly affected at the lowest dose examined (5 ppm). Also, the maximal induction ranged from 105-fold (CYP4A1) to less than 10-fold (FABP) relative to vehicle-treated animals. The accumulation of mRNA for ACO, FABP, and CYP4A1, but not c-myc, showed typical receptor-mediated dose–response relationships. The effects on gene expression were compared to rates of hepatic cell proliferation, a pertinent marker of tumor promotion and hepatocarcinogenesis. Surprisingly, ACO mRNA showed an excellent correlation (r2= 0.9) while c-myc mRNA exhibited a poor correlation (r2= 0.3) with cell proliferation in rat liver. Although the differences between the dose–response relationships of ACO and c-myc mRNA accumulation may suggest immediate early genes are not controlled by PPAR, evidence from PPARα null mice support this receptor in both lipid metabolism and growth regulatory genes. This study shows the complexity of responses mediated by peroxisome proliferators, with ACO being a good marker of PPAR-mediated events as well as cell proliferation, while c-myc, a known growth regulatory gene, was induced by Wy14,643 partially via PPAR but did not correlate well with cell proliferation.

Hepatocyte proliferation in rats after ventromedial hypothalamic lesions: immunoreactivity patterns of proliferating cell nuclear antigen (PCNA).

Ventromedial hypothalamic (VMH) lesions result in increased DNA content in the rat liver. However, little information is available concerning the proliferative activity and lobular distribution of different cell populations in VMH-lesioned rat liver. The aim of the present study was to quantitatively assess these parameters in VMH-lesioned rat liver by measuring proliferating cell nuclear antigen (PCNA) reactivity. We investigated to determine whether this mitotic response involves acinar zones 1, 2, or 3. Changes in immunohistochemical labeling indices in rat liver were measured with an antibody against PCNA until 7 days after VMH lesioning. The effects of hepatic vagotomy on proliferation were also examined. Proliferation of hepatocytes in acinar zones 1-3 began to increase on day 1, and reached a maximum at 3 days. The area of most intense proliferation progressively shifted from acinar zone 1 to zone 3 in several days. The proliferation was completely inhibited by hepatic vagotomy, indicating that VMH lesions induce cell proliferation in rat liver via hepatic vagus nerve activity. This study implicates the information available on neural factors which initiate hepatocyte proliferation.

Increased expression of c-fos, c-jun and LRF-1 is not required for in vivo priming of hepatocytes by the mitogen TCPOBOP.

The notion that an increased expression of immediate early genes such as c-fos and c-jun is an absolute requirement for the G0-G1 transition of the hepatocytes has recently been challenged by the finding that rat liver cell proliferation induced by primary mitogens may occur in the absence of such changes (Columbano and Shinozuka, 1996). To further investigate the relationship between immediate early genes and hepatocyte proliferation, we have compared the hepatic levels of c-fos, c-jun and LRF-1 transcripts during mouse liver cell proliferation in two conditions: (i) direct hyperplasia induced by the non-genotoxic hepatocarcinogen 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene, and (ii) compensatory regeneration caused by a necrogenic dose of carbon tetrachloride. The results show striking differences in the activation of early genes. In spite of a rapid stimulation of S phase by 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (approximately 8% of hepatocytes were BrdU-positive as early as 24 h after mitogen treatment versus 1% of labelled hepatocytes after 2/3 partial hepatectomy), no changes in the expression of c-fos, c-jun and LRF-1 could be observed. Moreover, no change in steady state mRNA hepatic levels of IGFBP-1 (a gene highly expressed in rat liver following partial hepatectomy), and only a slight increase in c-myc and PRL-1, was found after mitogen administration. On the contrary, a rapid, massive and transient increase in the hepatic mRNA levels of all these genes was observed during carbon tetrachloride induced regeneration. The results indicate that increased expression of immediate early genes may be dependent upon the nature of the proliferative stimulus, and it may not be a prerequisite in certain in vivo conditions such as proliferation induced in the absence of liver tissue damage.

Cyclin a mRNA expression during normal rat liver cell proliferation induced by partial hepatectomy or ethinylestradiol administration

Cyclin a mRNA expression during normal rat liver cell proliferation induced by partial hepatectomy or ethinylestradiol administration

Cyclin A mRNA expression during normal rat liver cell proliferation induced by partial hepatectomy or ethinylestradiol administration

Cyclin A mRNA expression during normal rat liver cell proliferation induced by partial hepatectomy or ethinylestradiol administration

Hepatocyte proliferation induced in rats by lead nitrate is suppressed by several tumor necrosis factor α inhibitors

Lead nitrate induces liver cell proliferation in rats without accompanying liver cell necrosis. However, the mechanism of this proliferation and its effect on hepatocytes remain unknown. Therefore, we examined the liver and blood level of hepatocyte growth factor and tumor necrosis factor α (TNF-α) at various intervals to determine whether lead nitrate modifies hepatocyte proliferation by altering the production of these cytokines. We also administered several TNF-α inhibitors, dexamethasone, adenosine, (2E)-3-[5-(2,3- dimethoxy-6-methyl-1,4-benzoquinoyl)]-2-nonyl-2-propenoic acid (E 3330), and pentoxifylline, to rats to clarify whether pretreatment with these inhibitors suppresses the increase of TNF-α messenger RNA (mRNA) in the liver and prevents the hepatocyte proliferation induced by lead nitrate. Hepatocyte proliferation occurred by 24 hours and reached a peak 48 hours after a single intravenous injection of lead nitrate (100 mumol/kg). TNF-α mRNA expression in the liver was increased 1, 6, and 12 hours after the injection, whereas no alteration was observed in liver or blood level of hepatocyte growth factor. Pretreatment with dexamethasone (4.0 mg/kg), E3330 (100 mg/kg) adenosine (0.3 mmol/kg), and pentoxifylline (100 mg/kg), inhibited both TNF-α mRNA expression and hepatocyte proliferation 48 hours after the injection. These experimental results strongly support the hypothesis that TNF-α positively regulates the hepatocyte proliferation induced in rats by the mitogen, lead nitrate.