Effects of calcium channel blocking agents on calcium and centrilobular necrosis in the liver of rats treated with hepatotoxic agents

Carbon tetrachloride, chloroform, dimethylnitrosamine, thioacetamide or acetaminophen was each administered to rats in a single hepatotoxic dose. Nifedipine, verapamil or chlorpromazine was administered in association with the hepatotoxic agents to determine if calcium channel blocking agents would prevent an increase in liver cell calcium associated with hepatotoxicity and to determine if these agents would protect against the development of centrilobular necrosis. Following a latent period different for each toxic agent, a 4- to 18-fold increase in liver cell calcium content had occurred by 24 hr. The calcium increase and the centrilobular necrosis (mean histologic score) were correlated. A relatively high calcium to necrosis ratio was obtained with dimethylnitrosamine, thioacetamide and acetaminophen. A lesser calcium to necrosis ratio was obtained with chloroform and carbon tetrachloride, the two toxic agents that destroyed the intracellular calcium sequestration activity of the liver endoplasmic reticulum. Nifedipine or chlorpromazine, administered prior to and 7 hr after the toxic agent, completely prevented the centrilobular necrosis caused by thioacetamide, carbon tetrachloride and acetaminophen; almost completely prevented necrosis with dimethylnitrosamine; and provided partial protection against chloroform toxicity. Two doses of verapamil provided partial protection against necrosis when carbon tetrachloride was the toxic agent and provided almost complete protection with dimethylnitrosamine. A reduction in liver cell calcium was associated with the protective action of the three calcium channel blocking agents. These findings are compared with earlier studies of the protective effects of calcium channel blocking agents in cardiac ischemia.     

Kinetic disposition of ethanol in the neonatal piglet and hemodynamic effects in the presence and absence of 4-methylpyrazole

The hemodynamic effects of acute ethanol intoxication and the kinetic disposition of ethanol are reported for the first time in neonatal piglets under nitrous oxide anesthesia. Two hours after a single dose of ethanol (1.4 g/kg), blood pressure decreased from 76 +/- 4 to 71 +/- 4 mm Hg (p less than 0.05) and heart rate increased from 194 +/- 10 to 227 +/- 8 beats/min (p less than 0.05; means +/- SE). By 5 hr, blood pressure dropped to 67.5 +/- 4 mm Hg and heart rate increased to 239 +/- 8 beats/min. In piglets pretreated with 4-methylpyrazole, an alcohol dehydrogenase inhibitor, there was a transient increase in blood pressure (p less than 0.05) and a decrease in heart rate (p less than 0.05) immediately after the end of the ethanol infusion. However, the hemodynamic alterations observed 2 hr after ethanol treatment alone were prevented with 4-methylpyrazole. These findings indicate that ethanol metabolites play a significant role in hemodynamic alterations observed after acute ethanol intoxication. The mean ethanol metabolic rate derived from plasma data was 94 +/- 9 mg/liter/hr. This corresponded to an apparent Km of 68 +/- 3 mg/liter and a Vm of 123 +/- 11 mg/liter/hr. The Vd was 0.966 +/- 0.031 liter/kg. The metabolic rate for ethanol, derived from plasma data, correlated with in vitro alcohol dehydrogenase activity at pH 7.4 and 25 and 37 degrees C. The optimum pH for hepatic alcohol dehydrogenase activity was 9.9.     

Bilirubin and S-nitrosothiols interaction: evidence for a possible role of bilirubin as a scavenger of nitric oxide

Bilirubin (BR), the final product of heme catabolism, plays a crucial role in the defense against reactive oxygen species in various cell types. In this study, we addressed the hypothesis that BR can act as a physiological scavenger of nitric oxide (NO), a gaseous mediator involved in many cellular functions and able to trigger the formation of reactive nitrogen species with pro-oxidant activity. We found that S-nitrosocysteine (SNOC) and S-nitrosoglutathione (GSNO), which have a half-life of 0.52+/-0.07 hr and 38+/-5 hr and release NO at a constant rate of 1.42+/-0.2 hr(-1) and 0.018+/-0.002 hr(-1), respectively, were able to decrease BR half-life in a concentration-dependent manner under physiological conditions. This effect appears to be dependent on NO formation as L-cysteine and GSH did not affect BR consumption and nitrite was four to five times less efficient than SNOC in reducing BR half-life. Oxyhemoglobin, a well-known scavenger of NO, protected BR from SNOC-mediated degradation. In addition, the reaction between SNOC/GSNO and BR modified the absorption spectrum of the bile pigment showing a gradual increase in the absorbance at 316 nm. This change in the BR spectrum indicates that the bile pigment could be a target for N-nitrosation reactions, since it resembles the modifications occurred when other molecules such as di-peptides and uric acid are nitrosated. Taken together, these data suggest that BR should not be considered only as an endogenous antioxidant but also as a molecule with the potential ability to counteract intracellular nitrosative stress reactions.     

Circadian rhythm of hepatic uridine phosphorylase activity and plasma concentration of uridine in mice

The activity of hepatic uridine phosphorylase (EC 2.4.2.3.) in male mice (24-29 g) maintained in standardized conditions of 12 hr light (0600-1800 hr) alternating with 12 hr darkness (1800-0600 hr), food and water ad lib., exhibited a circadian rhythm (P less than 0.0001, Cosinor analysis). The peak of enzyme activity (559 +/- 25 pmol/min/mg protein) occurred at 15 hr after light onset (HALO) with the nadir (139 +/- 25 pmol/min/mg protein) at 3 HALO when samples were taken every 4 hr. Female mice showed essentially the same pattern. A circadian rhythm (P less than 0.0001, Cosinor analysis) was also observed when the light-dark cycle was shifted (reverse cycle) so that the lights went on at 2200 hr and off at 1000 hr. Under the reverse cycle condition, there was a corresponding shift in the enzyme activity with a lag period of 3.5 hr in the time of maximum and minimum enzyme activities (i.e. the peak at 11 HALO and the nadir at 23 HALO) after a 2-week adaptation period. The lag period was reduced to 1 hr after 4 weeks of adaptation, and no further change was observed after 6 weeks of adaptation. The plasma concentration of uridine also exhibited a circadian rhythm (P less than 0.0001, Cosinor analysis) with peak concentration (10 microM) occurring at 2 HALO and a nadir (5 microM) at 14 HALO. The circadian rhythm observed in the plasma concentration of uridine is the inverse of that for uridine phosphorylase activity. These results demonstrate that hepatic uridine phosphorylase plays an important role in the regulation of the uridine level in the blood which, in turn, may be involved in the humoral control of sleep by uridine. This may also be of clinical significance in enhancing the antitumor efficacy of the 5-fluorinated pyrimidines by modulating the time of their administration.     

Evidence for the metabolism of N-nitrosodimethylamine and carbon tetrachloride by a common isozyme of cytochrome P-450

Carbon tetrachloride administration to rats produced a selective loss of hepatic cytochrome P-450-dependent catalytic activities. Of the cytochrome P-450-dependent catalytic activities tested, the metabolism of carbon tetrachloride to phosgene and the low Km N-nitrosodimethylamine demethylase were the most sensitive to destruction by carbon tetrachloride. A 50% or greater loss in these catalytic activities was observed 3 hr after giving 10 microliters carbon tetrachloride/kg. Related catalytic activities, such as the microsomal metabolism of carbon tetrachloride to chloroform and the high Km N-nitrosodimethylamine demethylase, were diminished less than 20% 3 hr after giving 10 microliters carbon tetrachloride/kg. To investigate further the relationship between the metabolism of N-nitrosodimethylamine and carbon tetrachloride, the effect of pyrazole, a known inducer of the low Km N-nitrosodimethylamine demethylase, on carbon tetrachloride metabolism was studied. Pyrazole treatment produced a 5.6-fold increase in the microsomal metabolism of carbon tetrachloride to phosgene and a 1.9-fold increase in the conversion of carbon tetrachloride to chloroform. The similarities between both the loss and the induction of the low Km N-nitrosodimethylamine demethylase and the metabolism of carbon tetrachloride to phosgene suggest that these catalytic activities represent a common isozyme of cytochrome P-450. Analysis of cytochromes P-450 by HPLC provided evidence for an isozyme of cytochrome P-450 inducible by pyrazole and destroyed by carbon tetrachloride.     

The role of acrolein in allyl alcohol-induced lipid peroxidation and liver cell damage in mice

Male NMRI mice were fed a sucrose diet for 48 hr in order to reduce the hepatic glutathione content and to level off its diurnal variation. After administration of allyl alcohol (AA: 1.1 mmol/kg), hepatic glutathione (24.3 +/- 7.0 nmol GSH/mg protein) was almost totally lost within the first 15 min (less than 0.5 nmol GSH/mg protein). Subsequently, a massive lipid peroxidation was observed, i.e. the animals exhaled 414 +/- 186 nmol ethane/kg/hr compared to 0.9 +/- 0.8 of controls, and the hepatic TBA-reactive compounds had increased from 55 +/- 16 pmol/mg protein in controls to 317 +/- 163 after 1 hr. Concomitantly, a 40-45% loss of the polyunsaturated fatty acids (arachidonic and docosahexaenoic acid) in the liver lipids was observed. About 80% of the cytosolic alcohol dehydrogenase activity and about 50% of the microsomal P450-content were destroyed. In vivo-inhibition of alcohol dehydrogenase by pyrazole or induction of aldehyde dehydrogenase by phenobarbital abolished AA-induced liver damage as well as glutathione depletion and lipid peroxidation, while inhibition of aldehyde dehydrogenase by cyanamide made a subtoxic dose of AA (0.60 mmol/kg) highly toxic. These results strongly favour the importance of acrylic acid formation as an additional detoxification pathway. Enhanced hepatic levels of glutathione protected in vivo against the damaging effects of AA. Depletion of the liver glutathione content by phorone or diethylmaleate alone caused marginally enhanced lipid peroxidation (phorone) but not liver cell damage. Monooxygenase inhibitors (metyrapone, diethyldithiocarbamate, alpha-naphthoflavone) or an inducer (benz(a)pyrene) did not affect AA-induced toxicity. The ferric iron chelator desferoxaminemethanesulfonate prevented AA-induced lipid peroxidation and liver cell damage in vivo. In vitro, acrolein alone failed to initiate lipid peroxidation in soy bean phospholipid liposomes or in mouse liver microsomes. Thus, acrolein not only impairs the glutathione defense system but also directly destroys cellular proteins and evokes lipid peroxidation by an indirect iron-depending mechanism.     

Nocturnal doses of ranitidine and nizatidine do not affect the disposition of diazepam

The disposition of diazepam (D) after a single oral dose of 10 mg was evaluated in nine healthy male volunteers under the following conditions (randomized, double-blind, crossover design): D + comedication of placebo and D + nocturnal dosing with 300 mg ranitidine or 300 mg nizatidine. Plasma concentrations of D and its major active metabolite, desmethyldiazepam (DD), were monitored by a gas-liquid chromatography-electron-capture detection assay for 84 hours. Neither ranitidine nor nizatidine had any significant effect on the hepatic elimination of D as characterized by its terminal half-life (mean +/- SD) of 35.3 +/- 24.2 hours (+ ranitidine: 30.1 +/- 9.9 hr; + nizatidine: 37.3 +/- 18.3 hr) or total plasma clearance of 28.2 +/- 12.0 mL/min (+ ranitidine: 26.5 +/- 7.9 mL/min; + nizatidine: 26.7 +/- 10.4 mL/min). Likewise, the formation of DD as measured by its AUC was not affected by ranitidine or nizatidine. Thus, it can be concluded that concomitant once-daily dosing (300 mg nocturnally) with ranitidine or nizatidine does not impair hepatic drug metabolism.     

Pharmacokinetics of paclitaxel in rabbits with carbon tetrachloride-induced hepatic failure

The pharmacokinetic of paclitaxel (1 mg/kg, i.v.) was investigated in rabbits with carbon tetrachloride-induced hepatic failure. The area under the plasma concentration-time curve (AUC) of paclitaxel was significantly (p<0.01) increased in severe carbon tetrachloride-induced hepatic failure rabbits (1,364.54 +/- 382.07 ng/ml x hr) compared to that of normal rabbits (567.52 +/- 141.88 ng/ml x hr), but not significantly in moderate carbon tetrachloride-induced hepatic failure rabbits (803.1 +/- 208.81 ng/ml x hr). The volume of distribution (Vd) (6.25 +/- 1.56 L) and the elimination rate constant(beta) (0.09 +/- 0.025 hr(-1)) of paclitaxel in severe carbon tetrachloride-induced hepatic failure rabbits were significantly (p<0.05) decreased compared to those of normal rabbits (11.65 +/- 2.91 L, 0.12 +/- 0.030 hr(-1)), but not significantly in moderate carbon tetrachloride-induced hepatic failure rabbits (9.46 +/- 2.37 L, 0.10 +/- 0.026 hr'). Total body clearance (CLt) of paclitaxel in severe carbon tetrachloride-induced hepatic failure rabbits (0.733 +/- 0.183 L/hr/kg) was significantly (p<0.01) decreased compared to that of normal rabbits (1.762 +/- 0.440 L/hr/kg), but not significantly in moderate carbon tetrachloride-induced hepatic failure rabbits (1.245 +/- 0.311 L/hr/kg). The half-life(t 1/2) of paclitaxel in severe carbon tetrachloride-induced hepatic failure rabbits (7.71 +/- 2.16 hr) was significantly (p<0.05) increased compared to that of normal rabbits (5.75 +/- 1.44 hr), but not significantly in moderate carbon tetrachloride-induced hepatic failure rabbits (6.77 +/- 1.76 hr). This results could be due to inhibition of paclitaxel metabolism in liver disorder rabbits since paclitaxel is essentially metabolized in liver. The findings suggest that the dosage regimen of paclitaxel should be adjusted when the drug would be administered in patients with liver disorder in a clinical situation.     

Conversion of retinol to retinal by rat liver microsomes.

An NADPH-requiring enzyme present in rat liver microsomes catalyzes the conversion of retinol to retinal; the enzyme activity is induced by 3-methylcholanthrene (MC). The optimum activities for both the constitutive and induced reactions occur within a pH range of 8.2-8.7. For the constitutive enzyme, the KM and Vmax values are 285 microM retinol and 18 nmol of retinal/mg protein/hr, respectively; for the MC-induced activity, the corresponding values are 133 microM retinol and 33 nmol of retinal/mg protein/hr. Neither the constitutive nor the induced activities are detectable in microsomes from seven other tissues. Both hepatic activities are inhibited by citral, ketoconazole, SKF 525-A, and alpha-naphthoflavone; both are stimulated by divalent cations. Neither is inhibited by 3-amino-1,2,4-triazole, pyrazole, or sodium azide or stimulated by monovalent cations. The enzyme appears to be a previously unreported retinol oxidase, distinct from the known cytosolic enzymes, retinal reductase and retinol dehydrogenase.     

The isoenzyme pattern of cytochrome P450 in rat hepatocytes in primary culture, comparing different enzyme activities in microsomal incubations and in intact monolayers

Changes in the isoenzyme pattern of cytochrome P450 during culture were investigated in primary cultures of rat hepatocytes, measuring specific enzyme activities in microsomes prepared from cultured cells as well as in intact monolayers. Assays of 7-ethoxyresorufin O-deethylation (EROD), 7-pentoxyresorufin O-depentylation (PROD), aniline 4-hydroxylation (AH) and the specific regioselective hydroxylation of testosterone were used as representatives of the activities of seven isoenzymes of cytochrome P450. The isoenzyme profile expressed as catalytic activities was qualitatively and quantitatively similar in microsomes obtained from freshly isolated hepatocytes in comparison with microsomes obtained from whole livers of untreated rats. There was a relatively high activity in EROD, AH and the oxidation of testosterone at the 7 alpha, 2 alpha, 6 beta, 16 alpha and 17 sites (androstenedione). During culture, these microsomal enzyme activities declined at a similar rate to ca. 50% of the activities of microsomes prepared from freshly isolated hepatocytes after 24 hr and to 15% after 96 hr. The overall decline of cytochrome P450-dependent activities during culture was not accompanied with gross changes in catalytic profile. Determining the same drug-metabolizing activities directly in intact hepatocyte monolayers revealed a much higher metabolic rate for all measured P450-dependent activities. The profile of the catalytic activities was essentially the same as measured in microsomes prepared from cultured hepatocytes. The relatively low activity towards the 7 alpha site of testosterone measured in intact hepatocytes, however, remained constant during culture. Determination of enzyme activities directly in intact hepatocytes is a convenient way of studying changes in monooxygenase activities of different P450 isoenzymes in vitro.     

Bevantolol disposition in patients with hepatic cirrhosis

Bevantolol is a new, cardioselective beta-receptor antagonist that undergoes extensive hepatic biotransformation. To evaluate changes in the disposition of bevantolol produced by liver disease, a single 200-mg oral dose of bevantolol was administered in ten patients who had hepatic cirrhosis and to ten age-matched controls. Cirrhotic patients had a greater plasma bevantolol half-life (6.9 +/- 4.0 hr, mean +/- SD) then did patients with normal liver function (2.8 +/- 1.1 hr, P less than .01), and they also had a longer duration of significant bevantolol-induced heart rate slowing (for 12 hours after oral dose in cirrhotics versus three hours for controls). On the other hand, the peak concentration after the oral dose and the magnitude of bradycardiac effect were similar for both groups. Plasma bevantolol half-life was more variable in cirrhotic patients than in controls. Some of this variability among cirrhotics was attributable to age, which was a significant determinant of bevantolol half-life in the cirrhotic (but not in the control) patient sample. These results indicate that hepatic cirrhosis alters the disposition of bevantolol and suggest that modifications in bevantolol dose should be considered when using this drug to treat patients with liver disease.     

The effect of griseofulvin on the heme pathway--II. An exhaustive analysis during short and long-term challenge.

1. A clear biphasic response of the enzyme activities as a function of intoxication time due to the topical cutaneous griseofulvin treatment was observed. 2. The initial acute induction of ALA-S activity would be due to depletion of free heme in the regulatory pool caused by cytochrome P 450 destruction. 3. The second induction peak, would be due to less heme formation, secondary to the ferrochelatase inhibition, as expected for the erythropoietic protoporphyria model. 4. The biphasic response of hepatic ALA-D and PBGase activities would be related to ALA-S activity changes and the subsequent augmented available substrates. 5. Endogenous liver porphyrin distribution in cytosolic, mitochondrial and nuclear fractions was investigated. 6. The in vitro biosynthesis of porphyrins confirmed both the biphasic model and the hepatic porphyrins subcellular distribution. 7. Two mechanisms to explain the action of griseofulvin at shorter and longer times of intoxication are proposed.     

Effect of dimethyl sulphoxide on oxidative stress, activation of mitogen activated protein kinase and necrosis caused by thioacetamide in the rat liver

Thioacetamide (400 mg/kg body weight, i.p.) was administered to rats. After 12 h the activity of plasma glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT) was significantly higher than that of the control group, and after 24 h plasma GOT and GPT activities strongly increased. These results indicated that the necrotic process was initiated at about 12 h and developed thereafter. By co-administration of dimethyl sulphoxide (DMSO, 18 and 1 h before, and 8 h after administration of thioacetamide: each time, 2.5 ml/kg body weight, p.o.), plasma GOT and GPT were significantly decreased and were even comparable to the control group, showing that DMSO totally prevented the necrotic action of thioacetamide. After 12 and 24 h of thioacetamide administration, the hepatic level of vitamin C, the most sensitive chemical indicator of oxidative stress, decreased significantly, indicating that oxidative stress was significantly enhanced 12 h after thioacetamide intoxication and thereafter. DMSO totally restored the liver vitamin C level, demonstrating that DMSO effectively ameliorated the oxidative stress caused by thioacetamide, resulting in the prevention of necrosis of the liver. Phosphorylated c-Jun NH(2)-terminal kinase (JNK) significantly increased transiently 12 h after treatment with thioacetamide. These results indicated that oxidative stress and the activation of JNK took place almost simultaneously. Phosphorylated extracellular signal-related kinase (ERK) 2 was significantly increased 6-12 h after thioacetamide injection. Phosphorylated p38 MAPK (mitogen activated protein kinase) was significantly decreased 24 h after administration of thioacetamide. DMSO treatment inhibited the change of these MAPKs by thioacetamide, corresponding with the prevention of the liver necrosis as well as the attenuation of oxidative stress.     

Kinetic properties and inhibition of Acinetobacter glutaminase-asparaginase

Kinetic parameters, substrate specificity and exclusivity of ligands at binding sites of L-glutaminase-L-asparaginase purified from Acinetobacter glutaminasificans were studied in order to gain knowledge about the dual activities of this enzyme and its inhibition by structural analogs. Both L-glutamine and L-asparagine, which showed similar Km (4 approximately 7 X 10(-5) M) and Vmax (molecular activity 1.0 min-1) values, were competitive with each other for the substrate binding site. The products, L-glutamic acid and L-aspartic acid, showed competitive inhibition with respect to either L-glutamine or L-asparagine as substrates. Multiple inhibition of the glutaminase activity by L-glutamic acid and L-aspartic acid indicated that these ligands are mutually exclusive at the product-releasing site. The initial rates of both of the enzyme's activities were competitively inhibited by the following inhibitors (in rates of both of the enzyme's activities were competitively inhibited by the following inhibitors (in decreasing order of activity): 6-diazo-5-oxo-L-norleucine (DON), L-methionine sulfoximine, azaserine, and Acivicin. DON and azaserine inhibited both the asparaginase and glutaminase activities in a time-dependent and irreversible manner. The kinetic data suggest an ordered mechanism with glutamine or asparagine as the first substrate and glutamic acid or aspartic acid, respectively, as the last product. These results also suggest that a single mechanism and a single set of binding sites are responsible for catalyzing both of the enzyme's activities. The data also showed that succinylated enzyme, which has a 10-fold increase of plasma half-life in animals and humans and, thus, has benefit as a cancer chemotherapeutic agent, retained its catalytic activity and maintained Km and Vmax values similar to the native enzyme.     

Efficacy, tissue distribution and biliary excretion of methyl (3R*,5S*)-(E)-3,5-dihydroxy-9,9-diphenyl-6,8-nonadienoate (CP-83101), a hepatoselective inhibitor of HMG-CoA reductase activity in the rat

Methyl (3R*,5S*)-(E)-3,5-dihydroxy-9,9-diphenyl-6,8-nonadienoate, CP-83101, was identified as a potent competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity, inhibiting enzyme activity in vitro with an IC50 of 8.5 +/- 0.7 microM and a Ki with respect to HMG-CoA of 2.6 microM. CP-83101 also inhibited rat hepatic sterol biosynthesis by 39 +/- 7% at a dose of 100 mg/kg. [3H]CP-83101, administered orally to rats, exhibited peak plasma levels at approximately 1 hr that declined thereafter with an apparent half-time of 2-3 hr. Peak tissue levels also occurred 1 hr following oral administration of [3H]CP-83101. The decline in radioactivity in the liver, however, was considerably slower than that noted in blood, whereas the half-life in non-hepatic tissues was approximately 1 hr. Liver/blood ratios of 14, and liver/lens ratios of greater than 3000, following oral administration of [3H]CP-83101, were similar to those previously reported for other HMG-CoA reductase inhibitors, suggesting a high degree of tissue selectivity. In addition, liver/adrenal and liver/ovary ratios were approximately 1000 at all time points examined between 30 min and 24 hr following oral [3H]CP-83101 administration, indicating a high specificity for hepatic versus other steroidogenic tissues. Evaluation of intravenous versus oral administration of the water-soluble, free acid, sodium salt of [3H]CP-83101 in bile duct canulated rats indicated that approximately 20% of orally administered CP-83101 is absorbed from the gastrointestinal tract, and that absorbed CP-83101 is cleared rapidly from the plasma via the liver and from the liver via the bile. In addition, several lines of evidence suggest that CP-83101 may undergo enterohepatic recirculation. Agents of this synthetic series may thus possess advantages over other HMG-CoA reductase inhibitors with respect to tissue kinetics and specificity.     

Immunological evidence for N-acetyltransferase isozymes in the rabbit

An immunological evaluation of N-acetyltransferase (NAT) (EC 2.3.1.5) in liver, duodenum, lung, and kidney of the rabbit is described. Polyclonal antibodies to hepatic NAT isolated from rapid acetylator rabbits were raised in a goat and utilized for immunoblot analyses and enzyme inhibition studies. Immunoblot analyses demonstrated that hepatic and duodenal cytosols from rapid but not slow acetylator rabbits contained an immunoreactive 33-kDa protein. No immunoreactivity was observed for lung or kidney cytosols from either rapid or slow acetylators. The inhibition of sulfamethazine and p-aminobenzoic acid acetylation by polyclonal antibodies was investigated using cytosols from rapid and slow acetylator rabbits. With rapid acetylator cytosols, maximal inhibition of hepatic, duodenal, and lung NAT activities was 94.4 +/- 9.0%, 92.5 +/- 8.5%, and 28.3 +/- 2.4%, respectively, for sulfamethazine (500 mM) acetylation and 90.1 +/- 8.0%, 80.2 +/- 6.4%, and 26.7 +/- 3.1%, respectively, for p-aminobenzoic acid (500 microM) acetylation. Using 25 microM p-aminobenzoic acid as substrate, maximal inhibition of NAT activity was 32.0 +/- 2.1% with liver cytosol and 5.8 +/- 0.16% with duodenal cytosol, whereas no inhibition of lung NAT activity was observed. Kidney NAT activity was not inhibited by the polyclonal antibodies. With slow acetylator cytosols, no inhibition of NAT activities was observed. It is concluded that at least two NATs are present in liver, duodenum, and lung of rapid acetylator rabbits. Furthermore, the principal NAT in liver and duodenum is immunologically related to the minor form of lung NAT and is antigenically distinct from kidney NAT of rapid acetylators. Hepatic, duodenal, lung, and kidney NAT(s) of slow acetylator rabbits is (are) immunologically distinct from the major hepatic NAT in rapid acetylators. The data support the model in which the hepatic polymorphism in rabbits is caused by the total lack of the major rapid acetylator hepatic NAT in the phenotypic slow acetylator animal. These observations may have significant implications in the organ-specific toxicities of carcinogens that undergo metabolic activation via N-acetylation.     

培菲康对硫代乙酰胺诱导的大鼠肝性脑病的保护作用

目的　探讨培菲康对硫代乙酰胺 (TAA)引起的大鼠肝性脑病 (HE)模型的作用及其机制。方法　利用大鼠TAAHE模型 ,观察活菌制剂培菲康对HE大鼠神经反射 ,血清氨浓度 ,血清氨基酸支 /芳比值 ,肝门静脉LPS浓度和肝脏病理损伤的影响。结果　培菲康能降低大鼠的HE等级 ,改善HE大鼠的神经反射 ;显著降低血氨和门静脉LPS浓度 ,升高氨基酸的支 /芳比值 ,减轻肝脏的病理损伤。结论　培菲康对TAA引起的大鼠HE有明显的保护作用 ,其作用机制与降低血氨、门静脉LPS浓度和升高血清氨基酸支 /芳比值有关     

Effects of an antitumoural rhodium complex on thioacetamide-induced liver tumor in rats. Changes in the activities of ornithine decarboxylase, tyrosine aminotransferase and of enzymes involved in fatty acid and glycerolipid synthesis

Rats were injected daily for 8 weeks with 50 mg of thioacetamide per kg to produce liver tumours. Some of these rats were given three doses of 50 mg of an antitumoural Rh(III) complex/kg at 14, 9 and 5 days before the end of the thioacetamide treatment. Thioacetamide decreased the rate of weight gain of the rats and the Rh(III) complex partly restored it. The activities of ATP citrate lyase, acetyl-CoA carboxylase and fatty acid synthetase in the livers were decreased by thioacetamide treatment and the Rh(III) complex partly reversed this effect. By contrast the activity of malic enzyme was increased by both thioacetamide and the Rh(III) complex and this effect probably relates to NADPH production for detoxification rather than for lipogenesis. Treatment with thioacetamide increased the rate of synthesis of di- and triacylglycerols from glycerol phosphate by liver homogenates, the activity of phosphatidate phosphohydrolase and the incorporation of [3H]glycerol into liver triacylglycerol in vivo. The Rh(III) complex did not produce a significant reversal of these effects of thioacetamide on glycerolipid synthesis. The total uptake of intraportally injected [3H]glycerol by the livers of thioacetamide treated rats was decreased and this was associated with a lowered activity of glycerol kinase. Thioacetamide increased the activity of hepatic ornithine decarboxylase by about 40-fold, but the Rh(III) complex did not reverse this effect. However, the decrease in tyrosine aminotransferase activity that was produced by thioacetamide was partly reversed by the Rh(III) complex. These results are discussed in relation to the tumour-promoting effects of thioacetamide and the antitumoural action of the Rh(III) complex.     

Effects of phenobarbital and 3-methylcholanthrene pretreatment on the plasma half-life and urinary excretion profile of theophylline and its metabolites in rats

The effects of the inducers of the hepatic microsomal enzyme system, phenobarbital and 3-methylcholanthrene, on theophylline plasma half-life and on the elimination of theophylline and its metabolites in urine and feces have been examined. The results indicate that induction of the hepatic microsomal drug-metabolizing enzyme system significantly decreases plasma theophylline half-life. In this respect, 3-methylcholanthrene was more effective than phenobarbital. Control theophylline half-life was 3.5 hr. After phenobarbital or 3-methylcholanthrene pretreatment, the theophylline half-life was 2.6 and 0.8 hr respectively. Thin-layer Chromatographie analysis of the urine showed three radioactive peaks corresponding to 1,3-dimethyluric acid, 1-methyluric acid and unchanged theophylline. Both inducing agents significantly increased the urinary elimination of 1,3-dimethyluric acid above that seen in control animals throughout the 24-hr collection period, but only 3-methylcholanthrene increased the total amounts of 1-methyluric acid excreted. Urinary elimination of unchanged theophylline was decreased from control values by both agents. A small, but not statistically significant, increase in the fecal elimination of radioactive material was also noted in the animals pretreated with phenobarbital. The results indicate that alteration in hepatic drug-metabolizing activity may markedly affect the in vivo biotransformation of theophylline.