Effects In Rat Liver Research Articles

Inhibition by dietary hydroquinone of acetylaminofluorene induction of initiation of rat liver carcinogenesis

Monocyclic phenolics (MPs) occur widely in foods, both naturally and as synthetic antioxidant additives. Several have been shown to inhibit the carcinogenicity of a variety of genotoxic carcinogens in various tissues. Hydroquinone (HQ), one of the simplest of the MPs, which occurs naturally as the glucose conjugate arbutin, was studied for its ability, at low dietary levels, to inhibit the initiating effects in the rat liver of the DNA-reactive carcinogen 2-acetylaminofluorene (AAF). Male Fischer 344 rats (F344), 8 weeks old at the start of the study, were allocated to six groups. HQ was fed daily ad libitum in PMI certified diet at either 0.05% (≈25 mg/kg bw/d) or 0.2% (≈100 mg/kg bw/d) for 13 weeks, starting one week before AAF administration was initiated, and at the same doses to two groups not receiving AAF. AAF was given intragastrically three times a week for 12 weeks at doses of 3 mg/kg bw in 0.5% carboxymethyl cellulose (CMC) to a basal diet group and two of the groups receiving HQ in the diet. Vehicle controls were fed basal diet and administered 0.5% CMC intragastrically three times a week. The rats were observed daily and body weights were taken before initial dosing and at weekly intervals thereafter. Body weight gain over time, terminal body weights and absolute (mg) and relative liver weights (relative to body weight) were measured. At the end of the study (13 weeks), DNA adducts ( 32P-postlabeling), cell proliferation (PCNA immunohistochemistry) and preneoplastic hepatocellular altered foci (HAF) (glutathione S-transferase-placental type immuno-histochemistry) were measured. No significant differences were observed in body weight gains or liver weights. AAF produced liver DNA adducts and at the low dose of HQ adduct levels were 90% of that for AAF alone, whereas at the high dose adducts were reduced by 33% ( p < 0.05). AAF exposure yielded about a 50% increase in hepatocellular proliferation and both HQ doses reduced the AAF-induced increases in proliferation by about 25%. Likewise, the AAF-induced GST-P-positive HAF per cm 2 of liver tissue were decreased by both doses of HQ by about 50%. Thus, under the conditions of this experiment, HQ at both 0.05% and 0.2% in the diet diminished AAF-induced cancer initiating effects in rat liver.

C/EBPβ contributes to hepatocyte growth factor-induced replication of rodent hepatocytes

Hepatocyte replication can be induced in vivo by hepatocyte growth factor (HGF), which might be used for gene therapy or to promote liver regeneration. However, the biochemical steps critical for this process are not clear. C/EBPbeta and C/EBPalpha are liver-enriched transcription factors that induce and inhibit hepatocyte replication, respectively. Because of their role in hepatocyte replication, this study examined the effect of HGF upon C/EBP proteins in vivo. Rats were treated with HGF, and the effect upon C/EBPs was evaluated in liver extracts. Normal or C/EBPbeta-deficient mice were treated with HGF, and the effect upon hepatocyte replication was determined. HGF had no effect in rat liver upon C/EBPalpha or C/EBPbeta mRNA, nuclear protein, or nuclear DNA binding activity. However, HGF increased phosphorylated p90-RSK and ERK to 18- and 3-fold normal, respectively. These kinases phosphorylate C/EBPbeta and increase its transcriptional activity. The percentage of hepatocytes that replicated in C/EBPbeta-deficient mice after HGF administration was only 1.1%, which was lower than the value of 6.6% for hepatocytes from HGF-treated normal mice (P=0.005). C/EBPbeta contributes to the induction of hepatocyte replication in response to HGF in rodents, which is likely due to post-translational modifications.

Thresholds for DNA-Reactive (Genotoxic) Organic Carcinogens

This paper reviews the evidence for thresholds for DNA-reactive carcinogens and presents dose response data for effects in rat liver of two DNA-reactive hepatocarcinogens, diethylnitrosamine and 2-acetylaminofluorene, which is consistent with thresholds.

Long-term imaging effects in rat liver after a single injection of an iron oxide nanoparticle based MR contrast agent.

To investigate the duration of liver R2* enhancement and pharmacokinetics following administration of an iron oxide nanoparticle in a rat model. Rats were injected with 0, 1, 2, or 5 mg Fe/kg of NC100150 Injection, and quantitative in vivo 1/T2* liver measurements were obtained between 1 and 133 days after injection. The concentration of NC100150 Injection was determined by relaxometry methods in ex vivo rat liver homogenate. At all dose levels, 1/T2* remained greater than control values up to 63 days after injection. In the highest dose group, 1/T2* was above control levels during the entire 133 day time-course investigated. There were no quantifiable amounts of NC100150 Injection present 63 days after injection in any of the dose groups. The half-life of NC100150 Injection in rat liver was dose dependent. For the lowest dose group, the degradation of the particles could be defined by a mono-exponential function with a half-life of eight days. For the 2 and 5 mg Fe/kg dose groups, the degradation was bi-exponential with a fast initial decay of seven to eight days followed by a slow terminal decay of 43-46 days. NC100150 Injection exhibits prolonged 1/T2* enhancement in rat liver. The liver enhancement persisted at time points when the concentration of iron oxide particles present in the liver was below method detection limits. The prolonged 1/T2* enhancement is likely a result of the particle breakdown products and the induction of ferritin and hemosiderin with increasing iron cores/loading factors.

Species differences in hepatic peroxisome proliferation, cell replication and transforming growth factor-β1 gene expression in the rat, Syrian hamster and guinea pig

The objective of this study was to evaluate species differences in the hepatic effects of three potent rodent peroxisome proliferators, namely methylclofenapate (MCP), ciprofibrate (CIP) and Wy-14,643 (WY), particularly with respect to effects on replicative DNA synthesis and transforming growth factor-β1 (TGF-β1) gene expression. Male Sprague–Dawley rats, Syrian hamsters and Dunkin–Hartley guinea pigs were given daily oral doses of 0 (corn oil) and 75 mg/kg MCP for periods of 6 and 21 days. Syrian hamsters and guinea pigs were also treated with 25 mg/kg CIP and 25 mg/kg WY. Relative liver weights were significantly increased in peroxisome proliferator-treated rats and Syrian hamsters, but not in guinea pigs. Hepatic peroxisomal (palmitoyl–CoA oxidation) and microsomal (lauric acid 12-hydroxylase) fatty acid oxidising enzyme activities and CYP4A isoform mRNA levels were significantly increased in rats and Syrian hamsters, whereas only minor effects were observed in the guinea pig. Replicative DNA synthesis was studied by implanting 7-day osmotic pumps containing 5-bromo-2′-deoxyuridine during study days −1 to 6 and 14 to 21. Hepatocyte labelling index values were increased by MCP in the rat, but neither MCP, CIP nor WY produced any significant effect on replicative DNA synthesis in the Syrian hamster and guinea pig. MCP treatment increased TGF-β1 and insulin-like growth factor II/mannose-6-phosphate (IGFII/Man6P) receptor gene expression in the rat. In the Syrian hamster, effects on TGF-β1 and IGFII/Man6P receptor gene expression were also observed in some instances, whereas TGF-β1 mRNA levels were essentially unchanged in the guinea pig. These results provide further evidence for marked species differences in response to rodent peroxisome proliferators. While peroxisome proliferators produce a wide spectrum of effects in rat liver, other species such as the Syrian hamster and guinea pig are less responsive and in the case of some endpoints (e.g., cell replication) may be refractory.

Diethylnitrosamine exposure-responses for DNA ethylation, hepatocellular proliferation, and initiation of carcinogenesis in rat liver display non-linearities and thresholds.

In previous exposure-response studies, we have documented non-linearities for some of the early effects in rat liver of diethylnitrosamine (DEN) and a near no-effect levels for initiation of promotable liver neoplasms at the lowest cumulative exposure of 0. 5 mmol/kg body weight; this in spite of formation of DNA adducts and induction of hepatocellular altered foci (HAF). To extend these investigations, in an initiation segment, young male F344 rats were administered four exposures of DEN ranging from a cumulative total of 0.25 mmol, which is half of the previously used low exposure, up to 2 mmol per kg body weight, an effective initiating exposure. These exposures were achieved by once weekly intragastric instillations of one-tenth the total exposures for up to 10 weeks. The initiation segment was followed by a 4 week recovery segment, to allow for remission of acute and subchronic effects of DEN, after which the groups were maintained on 0.06% phenobarbital in the diet for 24 weeks to promote liver tumor development in order to assess initiation. During and after initiation and at the end of recovery, selected groups were studied for several crucial effects involved in hepatocarcinogenicity. The low exposure produced a low-level of DNA ethylation at both 5 and 10 weeks of exposure, measured as O(4)-ethylthymidine, the most persistent promutagenic ethylation product. At the 5 week interval, the adduct values of the higher exposures were less than proportional to the increment of exposure, suggestive of nonlinearity. Assessment of cellular proliferation by staining for proliferating cell nuclear antigen revealed that the lowest exposure did not increase the replicating fraction of hepatocytes during the initiation (10 weeks) or recovery (4 weeks) segments, whereas in the three higher exposure groups, proliferation was increased in relation to dose and time. Preneoplastic HAF expressing glutathione S-transferase-placental-type were present at low multiplicity in control livers and their multiplicity was increased in all exposure groups by the end of exposure, at which time the increase in the high exposure group was disproportionately greater than the increment of exposure. After phenobarbital administration in the promotion segment, all exposure groups exhibited further HAF increases at 39 weeks. At the end of the promotion segment, no hepatocellular neoplasm was found in 80 controls or in 40 rats in the low exposure group. In the mid-low exposure group, which was the previously studied low exposure, only one adenoma was found, yielding a 3% incidence, while in the two higher exposure groups, 32 and 80% of rats exhibited liver neoplasms, which were increased disproportionately greater than the increments of exposure. Thus, the findings document non-linearities of early DEN effects and at the lowest cumulative dose, a no-effect level (NEL) or threshold for initiation of promotable liver neoplasms. These findings provide a conceptual basis for understanding why low-level exposures to DNA-reactive carcinogens may convey no cancer risk.

Carcinogenic and anticarcinogenic effects of dehydroepiandrosterone in the liver of male and female rats

Dehydroepiandrosterone (DHEA), an adrenal steroid in humans, shows a certain anticarcinogenic effect in rat liver when it is administered simultaneously with strong carcinogens such as N-nitrosomorpholine (NNM). On the other hand, DHEA is an hepatocarcinogen in the rat when administered at high doses for more than 18 months. The hepatocellular tumors arise from amphophilic cell foci and exhibit a well-differentiated pheno-type. Wlien administered subsequent to NNM, DHEA acts as a tumor promoter in rat liver. Preneoplastic lesions of the glycogenotic/basophilic cell lineage induced by NNM are modulated to amphophilic lesions by DHEA. Female animals are more sensitive than males in respect of the carcinogenic and tumor-enhancing effect of DHEA. The higher sensitivity in females may be due to higher blood levels of DHEA andlor different metabolism and elimination of the drug, as compared to males. DHEA markedly induces cytochrome P450IVA, particularly in the liver of male rats. This effect may explain the rapid metabolism and elimination of the substance and the lower carcinogenicity in males. Both preneoplastic amphophilic foci and neoplasms are characterized by a strong proliferation of mitochondria. DHEA also induces peroxisome proliferation and susceptibility to lipid peroxidation in both genders. Furthermore, DHEA causes a reduction in activity and expression of key enzymes of carbohydrate metabolism and of glycogen content in the liver, which may be related to modulation of hepatocarcinogenesis.

3,5-Di-iodo-L-thyronine suppresses TSH in rats in vivo and in rat pituitary fragments in vitro.

3,5-Di-iodo-L-thyronine (T2) is a naturally occurring metabolite of thyroxine (T4). Contrary to earlier findings, T2 has recently been shown to have rapid effects in rat liver and in mononuclear blood cells. In the experiments described here, T2 was tested to determine whether it has a TSH suppressive effect in rats in vivo and in rat pituitary fragments in vitro. In experiments over 2 weeks in rats in vivo, low doses of T2 (20-200 micrograms/100 g body weight per day) had no significant influence on body and organ weights, but significantly decreased TSh and T4 serum concentrations. At 200 micrograms/100 g per day, T2 suppressed TSH to 43% and T4 to 29% of control levels. At 1-15 micrograms/100 g per day, 3,5,3'-tri-iodo-L-thyronine (T3), used as a comparison to T2, had significant effects on TSH and T4 levels, and also on body weight. Fifteen micrograms T3/100 g per day decreased TSH to 44%, T4 to 25%, and body weight to 59% of control levels. In experiments over 3 months in rats in vivo, a low dose (25 micrograms/100 g per day) of T2 suppressed TSH to 60% and T4 to 57% of control levels and had no significant influence on other parameters. Conversely, 0.1 microgram/100 g per day T3 had significant effects on body and organ weights as well as pellet intake, but a less pronounced TSH suppressive effect: TSH concentrations were unchanged and T4 concentrations were down to 80% of control values.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatic uptake of intact glutathione S-conjugate, inhibition by organic anions, and sinusoidal catabolism

To identify potential mechanisms for hepatic removal of circulating glutathione (GSH) conjugates, uptake and metabolism of S-2,4-dinitrophenylglutathione (DNP-SG) were examined in isolated perfused livers from rat and guinea pig. Guinea pig livers perfused with 5 mumol of DNP-SG in a recirculating system (50 microM initial concn) rapidly cleared the conjugate from the perfusate (half time 3.7 min), whereas clearance was considerably slower in rat liver (half time 35 min). Disappearance of DNP-SG from the perfusate was accompanied by a simultaneous appearance of DNP-SG and its metabolites in bile. Addition of acivicin, an inhibitor of gamma-glutamyltransferase (gamma-GT), to the perfusate resulted in a marked decrease in DNP-SG clearance by guinea pig liver but had no effect in rat liver, suggesting that in the guinea pig this process is largely dependent on sinusoidal gamma-GT activity. However, even in the presence of acivicin, rat and guinea pig livers removed nearly one-half of the administered DNP-SG from the recirculating perfusate over 30 min. High concentrations of DNP-SG were found in bile (up to 3.7 mM), indicating that the liver is capable of transporting the intact conjugate from the circulation. When rat livers were perfused with higher concentrations of DNP-SG (100 and 250 microM), biliary excretion of DNP-SG increased dose dependently, with concentrations in bile reaching 10 mM at the higher dose. This was accompanied by a dose-dependent choleresis.(ABSTRACT TRUNCATED AT 250 WORDS)

Ciprofibrate, a carcinogenic peroxisome proliferator, increases the phosphorylation of epidermal‐growth‐factor receptor in isolated rat hepatocytes

Ciprofibrate, a hypolipidaemic drug with carcinogenic and peroxisome-proliferation effects in rat liver, was found to increase the phosphorylation of epidermal-growth-factor receptor in 32P-labeled isolated rat hepatocytes. This effect was suppressed by protein-kinase-C inhibitors, and was accompanied by an almost complete inhibition of the receptor autophosphorylation normally induced by its ligand. However, in vitro experiments showed that protein-kinase-C phosphorylation of purified epidermal-growth-factor receptor was activated by ciprofibroyl-CoA, the acyl-CoA derivative of the drug, but not by the unmodified drug. Neither compound affected the ligand induction of epidermal-growth-factor-receptor autophosphorylation in isolated liver membranes. These results suggest that metabolically produced ciprofibroyl-CoA in liver cells would activate protein-kinase-C and produce changes in epidermal-growth-factor-receptor function.

Demonstration of ryanodine-induced metabolic effects in rat liver

The effects of ryanodine, a plant alkaloid which alters Ca 2+ sequestration in the liver, on O 2 uptake and gluconeogenesis were measured. Ryanodine administration to perfused rat liver resulted in the stimulation of O 2 uptake and of gluconeogenesis. Because ryanodine does not affect directly mitochondrial respiration, its stimulatory effect on O 2, uptake in the whole cell is likely to be secondary to the increased cytosolie free Ca 2+ levels.

Nervous control of liver metabolism and hemodynamics.

Besides being a center of intermediary metabolism, a center of defense and a control center for the hormonal system, the liver acts as the glucose reservoir of the organism and, moreover, as an important blood reservoir, by taking up or releasing glucose and blood. The many diverse hepatic functions are controlled by the substrate concentrations in blood, the cirulating hormone levels, the biomatrix and the autonomic hepatic nerves. In this review, the present knowledge of the metabolic and hemodynamic effects, the mechanism of action and the function of the hepatic nerves, as studied in the isolated perfused liver, are summarized.Effects of heptic nerve stimulationIn perfused rat liver, activation of the sympathetic liver nerves increases glucose and lactate release, urate and allantoin formtiuon, decreases ketogenesis, urea release, ammonia uptake, xenobiotics conjugation, bile flow and bile acid secretion as well as oxygen utilization, and causes an overflow of noradrenaline into the hepatic vein. Furthermore, sympathetic stimulation decreases the flow and elicits an intrahepatic redistrubution as well as a mobilization of blood by the closing of sinusoids. Activation of parasympathetic nerves enchances glucose utilization and causes re‐opening of previously closed sinusoids. The actions of hepatic nerves are modulated by the hormones glucagon, insulin, adrenaline, noradrenaline, vasopressin and angiotensin.Extrahepatocellular signal chain of sympathetic nerve stimulationThe release of noradrenaline from the nerve endings and all effects of electrical nerve stimulation are strictly dependent on the presence of extracellular calcium. Sympathetic nerves regulate the hepatic metabolism of carbohydrates and ketone bodies and the conjugation of xenobiotics directly via interaction with non‐parenchymal and parenchymal liver cells. However, sympathetic nerves regulate metabolism of nitrogenous compounds indirectly via reduction of blood flow. Studies with adrenergic and prostanoid agonists and antagonists support the following mechanism. Noradrenaline, released from the nerve endings via α1‐adrenergic receptors, directly interacts with periportal hepatocytes and also stimulates prostanoid formation in nearby non‐parenchymal liver cells. Prostanoids, in turn, modulate metabolism in parenchymal cells. About 50% of the metabolic nerve effects in rat liver are mediated via signal propagation through gap junctions. By this mechanism, rat liver apparently compensates the scarce innervation of only a few parenchymal and non‐parenchymal cells in the proximal periportal zone.Intrahepatocellular signal chain of sympathetic nerve stimulationSympathetic nerve stimulation of the perfused rat liver causes an increase in the activity of glycogen phosphorylase and a decrease in the activity of glycogen synthase, but leaves the activity of pyruvate kinase unaltered; fructose 2,6‐bisphosphate and cAMP are only slightly enhanced. Various studies strongly support the notion that the intracellular signal chain is propagated by production of inositol 1,4,5‐triphosphate and an increase in cytosolic calcium.In conclusion, hepatic nerves, together with the hormonal system, are directly involved in the regulation of liver metabolism and hemodynamics.

Effects of polychlorinated biphenyls on cytochrome P450 induction in the chick embryo hepatocyte culture

The effects of pure synthetic polychlorinated biphenyl (PCB) congeners on the induction of cytochrome P450 and associated activities were examined in cultured chick embryo hepatocytes. Dose-response effects for the induction of total cytochrome P450, ethoxyresorufin- O-deethylase (EROD) activity, and benzphetamine demethylase (BPDM) activity were studied using 10 selected tetra- to hexachlorinated PCB congeners. These studies revealed that PCBs caused effects in the chick hepatocyte culture different from previously observed effects in rat liver. Based on their effects in chick hepatocytes, the PCBs could be categorized into two groups. The first group (consisting of 3,3′,4,4′-PCB, 3,3′,4,4′,5-PCB, 3,3′,4,4′,5,5′-PCB, 2′,3,3′,4,5-PCB, 2,3,3′,4,4′,5′-PCB, and 2,3,4,4′,5-PCB) induced total cytochrome P450 2.4- to 2.9-fold and EROD activity from 1–2 pmol/min/mg protein to 162–247. There was marked variation in potency, but all these congeners had a maximal inducing dose above which cytochrome P450 concentrations and EROD activities declined. BPDM activities were increased only slightly (1.2- to 1.6-fold) at the maximal cytochrome P450 inducing dose. The second group of congeners (consisting of 2,2′,4,5,5′-PCB, 2,2′,4,4′,5,5′-PCB, and 2,2′,3,4,4′,6-PCB) induced total cytochrome P450 concentrations 4.0-fold and BPDM activities 2.2- to 2.6-fold with greatest activity occurring at the highest doses which could be added (10–50 μ m). However, EROD activities were also increased by these congeners to 60–112 pmol/min/mg protein with declining activities seen at the highest PCB doses (i.e., resembling EROD induction patterns of the first group). The EROD induction patterns with these latter PCB congeners are noteworthy since these PCBs do not induce EROD activity in the rat. For both groups of PCB congeners, EROD induction was associated with increased accumulation of uroporphyrin in cultures exposed to exogenous 5-aminolevulinate. Studies investigating the reason for the depression of cytochrome P450 concentrations and/or EROD activities by high doses of the PCBs revealed that with the first group there was slightly decreased total protein synthesis, decreased total cell heme concentrations, and decreased accumulation of radiolabeled heme synthesized from 5-[ 14C]aminolevulinate. These changes might represent nonspecific toxic effects of the first group of PCBs. However, since these changes were not seen with the second group of PCBs, it is unlikely that either inhibition of heme synthesis or toxicity cause the depression of EROD activity With high PCB doses.

Beta-naphthoflavone pretreatment reduces the genotoxic effect in rat liver by 2-nitrofluorene and 2-acetylaminofluorene

Beta-naphthoflavone pretreatment reduces the genotoxic effect in rat liver by 2-nitrofluorene and 2-acetylaminofluorene

Multisystem toxicity of indomethacin: Effects on kidney, liver and intestine in the rat

Some studies on the relationships among toxic effects in rat liver, kidney and intestine have been carried out. Indomethacin caused a marked reduction in microsomal enzymes, such as cytochrome P450, cytochrome b5 and aminopyrine N-demethylase in the kidney and the liver, greater in the former and for a shorter time than in the latter. Indomethacin induced intestinal lesions and marked overgrowth of intestinal bacteria, mainly of aerobic bacteria in the first 24 hours after its administration and anaerobic bacteria such as Clostridii in the second day. These findings enable us to suggest that the drug induces multisystem lesions through different mechanisms involving either a direct effect on the tissue or other microbiological or pharmacological factors.

Effects of estrogen and prolactin on thymidylate synthetase and thymidine kinase activities in N-nitrosomethylurea-induced rat mammary tumors

Methylglyoxal bis(butylamidinohydrazone) (MGBB) inhibited S-adenosylmethionine decarboxylase (SAMDC) activity competitively with S-adenosylmethionine (SAM) showing the Ki value of 1.8 × 10−5 M. MGBB showed less SAMDC-stabilizing effect in rat liver in vivo than did methylglyoxal bis(guanylhydrazone) (MGBG). MGBB inhibited the growth of human erythroid leukemia K 562 cells. Putrescine, spermidine and spermine concentrations in MGBB-treated cells were depressed to 56%, 58% and 88% of the values of control cells, respectively. [35S]Methionine incorporation into trichloroacetic acid-insoluble fraction was decreased in the inhibitor-treated cells.

Antitumor effect of methylglyoxal bis(butylamidinohydrazone), a new inhibitor of S-adenosylmethionine decarboxylase, against human erythroid leukemia K 562 cells

Methylglyoxal bis(butylamidinohydrazone) (MGBB) inhibited S-adenosylmethionine decarboxylase (SAMDC) activity competitively with S-adenosylmethionine (SAM) showing the K i value of 1.8 × 10 −5 M. MGBB showed less SAMDC-stabilizing effect in rat liver in vivo than did methylglyoxal bis(guanylhydrazone) (MGBG). MGBB inhibited the growth of human erythroid leukemia K 562 cells. Putrescine, spermidine and spermine concentrations in MGBB-treated cells were depressed to 56%, 58% and 88% of the values of control cells, respectively. [ 35S]Methionine incorporation into trichloroacetic acid-insoluble fraction was decreased in the inhibitor-treated cells.

Absence of a promoting or sequential syncarcinogenic effect in rat liver by the carcinogenic hypolipidemic drug nafenopin given after N-2-fluorenylacetamide

The hypolipidemic agent nafenopin, (NF), has been reported to be carcinogenic to rat liver. To determine whether nafenopin exerts a promoting or syncarcinogenic effect in rat liver, its effect on liver carcinogenesis induced by N-2-fluorenylacetamide (FAA) was studied. In two separate experiments, male F344 rats were fed 0.02% FAA for either 10 or 8 weeks to induce preneoplastic liver lesions. Following a recovery period of 1 week, rats were given 0.01 or 0.02% NF in the diet for 23 weeks in one experiment and 0.05 or 0.1% for 24 weeks in the other. The final incidence of neoplasms, and their numbers, size distribution, and degrees of differentiation were not significantly different in groups given NF after FAA compared to those maintained on a basal diet after FAA. In the group treated with the highest dose level of NF following FAA, however, there was a decrease in the number of grossly visible small neoplasms. In contrast, the liver neoplasm promoter phenobarbital increased the multiplicity, although not the incidence, of liver neoplasms when given after FAA. Thus, four different dose levels of NF showed no promoting or syncarcinogenic effect on FAA-induced hepatocarcinogenesis.

Syncarcinogenic effects on the initiation of rat liver tumors by trans-4-acetylaminostilbene and 2-acetylaminofluorene

Two carcinogenic aromatic amines with different organotropism were tested for syncarcinogenic effects in rat liver in an initiation-promotion experiment. Trans-4-acetylaminostilbene (AAS) and 2-acetylaminofluorene (AAF) were administered as initiators in four doses each either alone or sequentially combined in both orders. The promotion phase was started by partial hepatectomy and continued by adding phenobarbital (250 p.p.m.) to the drinking water for 26 weeks. The number/cm2 of tissue section and average size of hyperplastic foci, glucose-6-phosphatase-deficient and gamma-glutamyl-transpeptidase-positive foci were determined and a total area of lesions calculated during the promotion phase after 18 and 31 weeks, and in the post-promotion phase after 42 and 47 weeks. The synergistic effects of AAS and AAF were clearly more than additive if compared with the sum of the effects exerted by each compound individually. The sequence in which both initiators were administered remarkably influenced the development of lesions. They developed more rapidly and persisted longer in the post-promotion phase when AAS was administered first and AAF second. In the final stage, enzyme altered foci increased in the livers of both combination groups, but to a greater extent in the AAS-AAF group. It is concluded that the two arylamides damage DNA independently. In addition, however, the results suggest that AAS acts predominantly as an initiator, and AAF as a weak initiator and a strong promoter in what is considered the initiation phase of this experiment.

CGP 4718 A, a new potential antidepressant with a dual mode of action

CGP 4718 A (4-[5-chloro-benzofuranyl-2-]-1-methylpiperidine HCl) was found to inhibit MAO A preferentially in vitro in a competitive manner. Assessment of its in vivo effects by an ex vivo approach showed it to be a relatively weak, reversible inhibitor of MAO A. There were also effects on MAO B but they were inferior by a factor of about 10. The onset of the inhibitory effects in rat liver and brain was rapid, being maximal in about 1 h following administration of CGP 4718 A p.o. The inhibition was of relatively short duration with the effects being undetectable 24 h after treatment. CGP 4718 A also inhibited the reuptake of serotonin (5-HT) in synaptosomes in vitro and ex vivo. Evidence for 5-HT uptake inhibition was also found by using the H 75/12 depletor model. Its in vitro and in vivo potency as a 5-HT uptake inhibitor was approximately the same as that of imipramine. The effects on MAO A and on 5-HT uptake occurred over a similar dose range (above 10 mg/kg p.o.)and also had a similar time course. No evidence for inhibitory effects on noradrenaline uptake was found in vivo.