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S A Belinsky

Publications and source records attributed to S A Belinsky.

At least 73 records · Page 4Linked to original sources
PubMed1987

Molecular dosimetry of O6-methylguanine formation and cell toxicity in lung and nasal mucosa by 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone.

The molecular dosimetry of O6-methylguanine (O6-meG) in DNA from lung and nasal mucosa was determined during administration of 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK) to Fischer 344 rats. O6-MeG accumulated in lung during 12 days of treatment with doses of NNK ranging from 0.1 to 100 mg/kg per day. The dose-response to NNK was nonlinear; the ratio of O6-meG to dose, an index of alkylation efficiency, increased dramatically as the dose of carcinogen decreased. These data suggest that high and low Km pathways may exist for activation of NNK to a methylating agent. Clara cells, when compared to Type-II cells, macrophages and alveolar small cells, were found to possess the greatest concentration of O6-meG. Moreover, as the dose of NNK was decreased, a marked increase in the alkylation efficiency of Clara cells was observed. Thus, the presence of a high-affinity, low-Km pathway in Clara cells for activation of NNK may be a significant factor in the carcinogenicity of this tobacco-specific carcinogen. The dose-response for O6-meG differed considerably between respiratory and olfactory mucosa. The dose-response to NNK was nonlinear in respiratory mucosa and linear in the olfactory mucosa, and the concentration of O6-meG was five times greater in respiratory than in olfactory mucosa after treatment with 1 mg/kg NNK. As the dose of NNK was increased, alkylation in the two regions of the nose became similar. Histological examination of the nasal passages following treatment with NNK indicated that the olfactory region was more sensitive than the respiratory region to toxicity induced by NNK.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Mechanism of hepatotoxicity in periportal regions of the liver lobule due to allyl alcohol: studies on thiols and energy status.

The possible involvement of thiols and adenine nucleotides in the selective toxicity to periportal regions by allyl alcohol was evaluated in isolated perfused rat livers. Infusion of allyl alcohol (350 microM) for 20 min depleted hepatic glutathione content by 95% in both regions of the liver lobule yet damage was undetectable as indexed by release of lactate dehydrogenase or uptake of trypan blue. Perfusion for an additional 40 min in the absence of allyl alcohol resulted in lactate dehydrogenase release (2400 U/l) and uptake of trypan blue by 75% of hepatocytes in periportal regions of the liver lobule; however, dye was not taken up by cells in pericentral areas. Because thiol content was depleted in the undamaged pericentral area, it was concluded that thiol depletion alone cannot explain local toxicity to periportal regions by allyl alcohol. Perfusion with dithioerythritol (1.5 mM) prevented damage due to allyl alcohol totally. In contrast, addition of dithioerythritol 20 min after allyl alcohol did not prevent allyl alcohol-induced damage to periportal regions indicating that irreversible changes occur during the first 20 min which ultimately lead to damage. Fasting or pretreatment of rats with diethylmaleate (0.7 g/kg; 1 hr) to deplete glutathione decreased the T1/2 required for release of lactate dehydrogenase from 45 to 35 and 22 min, respectively. When methionine was infused into livers from diethylmaleate-treated rats, the T1/2 for release of lactate dehydrogenase by allyl alcohol was increased to 45 min. Infusion of allyl alcohol for 60 min also produced a significant decrease in ATP content and in the ATP/ADP ratio in periportal but not pericentral regions of the liver lobule.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Propanol↗
PubMed1986

Mechanism of hepatotoxicity to periportal regions of the liver lobule due to allyl alcohol: role of oxygen and lipid peroxidation.

The objective of this study was to evaluate the role of local oxygen tension in the zone-specific hepatotoxicity due to allyl alcohol. Infusion of allyl alcohol (350 microM) for 60 min into livers from normal fed rats perfused in the anterograde direction damaged virtually all cells in periportal areas of the liver lobule as indexed by trypan blue uptake (half-maximal uptake at 38 min). Under these conditions, oxygen uptake was inhibited only in periportal hepatocytes. Increasing the time of infusion of allyl alcohol to 90 min, however, caused dye uptake in virtually all cells across the liver lobule, with half-maximal staining in pericentral regions occurring at 70 min, indicating that hepatocytes in pericentral areas are not immune to damage by allyl alcohol. In livers from diethylmaleate-treated rats, the half-time for staining of periportal and pericentral regions was 27 and 39 min, respectively. Perfusion in the retrograde direction reverses the oxygen gradient in the liver. When allyl alcohol was infused in the retrograde direction for 60 min, cells in pericentral regions took up trypan blue whereas those in periportal areas were not damaged. Concomitantly, oxygen uptake was decreased only in pericentral regions. Infusion of allyl alcohol in oxygen-saturated perfusate in either direction caused release of lactate dehydrogenase and malondialdehyde. If oxygen tension was decreased by lowering the flow rate or perfusing with air-saturated buffer in the anterograde direction, however, malondialdehyde release and dye uptake due to allyl alcohol was reduced markedly.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Propanol↗
PubMed1986

Accumulation and persistence of DNA adducts in respiratory tissue of rats following multiple administrations of the tobacco specific carcinogen 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone.

4-(N-Methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a major nitrosamine formed in tobacco smoke, induces a high incidence of lung, liver, and nasal cavity tumors in rats. Since alpha-hydroxylation of NNK by target tissues can lead to the generation of a methylating agent, the formation and removal of 7-methylguanine and the promutagenic lesions O6-methylguanine (O6mGua) and O4-methyldeoxythymidine were determined over 12 days of NNK administration to rats (100 mg/kg/day). DNA alkylation was greatest in the nasal mucosa, followed by liver and lung after 1 dose of NNK. No DNA adducts were detected in kidney and brain under these conditions. The concentration of O6mGua increased steadily in lung throughout the treatment regimen, while O6-methylguanine-DNA methyltransferase decreased to less than 5% of control. The concentration of O4-methyldeoxythymidine in lung DNA reached a steady state after 4 days of carcinogen treatment. After NNK treatment was discontinued, O6mGua persisted, while O4-methyldeoxythymidine was removed rapidly in the lung, suggesting that different repair pathways exist for the removal of these adducts in vivo. In hepatocytes, nonparenchymal cells, and nasal mucosa, O6mGua concentrations were maximal after 1-2 days and declined by 50-80% during the remaining 10 days of treatment. The decrease in O6mGua levels in nasal mucosa paralleled a decline in O6-methylguanine-DNA methyltransferase activity and was associated with marked cytotoxicity to Bowman's glands, portions of the lateral nasal gland, and the olfactory and respiratory mucosa during carcinogen treatment. In contrast, the decline in O6mGua in hepatocytes was attributed to the induction of O6-methylguanine-DNA methyltransferase activity, since an 18-fold reduction in the ratio of O6mGua:7-methylguanine was observed over the 12 days of treatment. These studies have demonstrated a marked accumulation of promutagenic DNA adducts in target tissues during repeated exposure to NNK.

Animals↗
PubMed1985

Rates of pentose cycle flux in perfused rat liver. Evaluation of the role of reducing equivalents from the pentose cycle for mixed-function oxidation.

Rates of NADPH production via the pentose phosphate cycle were determined in perfused livers from phenobarbital-treated rats by measuring 14CO2 production from [1-14C]glucose infused in the presence and absence of p-nitroanisole (0.2 mM), a substrate for mixed-function oxidation. In the fed state, basal rates of NADPH generation were 34-44 mumol/g/hr. p-Nitroanisole, which was metabolized at rates of 8.9 mumol/g/hr, stimulated pentose cycle-dependent NADPH production by 21-24 mumol/g/hr. Fasting for 24 hr prior to perfusion diminished pentose cycle flux by 80% and largely abolished the stimulation of the pentose cycle by p-nitroanisole. In contrast, rates of p-nitroanisole O-demethylation were only diminished slightly, to 5.7 mumol/g/hr. Fasting decreased hepatic glucose, glucose 6-phosphate, and 6-phosphogluconate contents drastically as expected. Pretreatment of rats with 6-aminonicotinamide, which is metabolized to a potent inhibitor of 6-phosphogluconate dehydrogenase, decreased rates of NADPH generation via the pentose cycle to 6.9 mumol/g/hr but did not alter rates of p-nitroanisole metabolism (8.8 mumol/g/hr). Basal rates of NADPH generation decreased from 38 to 26 mumol/g/hr during infusion of potassium cyanide (2 mM), an inhibitor of mitochondrial energy metabolism. Cyanide also decreased rates of p-nitroanisole O-demethylation by over 60%; however, stimulation of NADPH generation via the pentose cycle by p-nitroanisole was as great in the presence (17-21 mumol/g/hr) as in the absence of cyanide. Since rates of mixed-function oxidation were unaffected after virtually complete inhibition of the pentose cycle with 6-amino-nicotinamide, it is concluded that reducing equivalents for the mixed-function oxidation of p-nitroanisole are not provided by the pentose cycle under these conditions.

6-Aminonicotinamide↗
PubMed1984

Calcium-mediated inhibition of glucuronide production by epinephrine in the perfused rat liver.

Rates of production of p-nitrophenyl glucuronide by isolated perfused livers from fed or fasted phenobarbital-treated rats were estimated by monitoring the concentration of glucuronide in the effluent perfusate. Infusion of epinephrine decreased the steady state level of p-nitrophenyl glucuronide by about 39% (half-maximal inhibition at approximately 5 microM). This result was unexpected because epinephrine activated glycogenolysis and elevated hepatic UDP-glucuronic acid contents. The effect of epinephrine can be attributed to its interaction with alpha-adrenergic receptors, since the inhibition of glucuronide production by epinephrine was reversed by an alpha-antagonist (phentolamine) but not by a beta-antagonist, propranolol. Since alpha-adrenergic agonists increase the cytosolic free calcium concentration, we investigated the possibility that the decrease in glucuronide production elicited by epinephrine was mediated by calcium. Removal of calcium from the perfusion fluid diminished the inhibition of glucuronide production by epinephrine, while increasing extracellular calcium from 0 to 150 microM restored the inhibition in a dose-dependent manner. In the presence of extracellular calcium, glucuronide production was inhibited by the addition of the calcium ionophore A23187 or angiotensin II, a hormone which increases cytosolic calcium. Concentrations of ionized calcium comparable to physiological intracellular levels (0.1-2 microM) increased microsomal beta-glucuronidase activity by 50 to 100% but had no effect on microsomal glucuronosyl-transferases . These results indicate that activation of hepatic alpha-adrenergic receptors increases cytosolic calcium which stimulates microsomal beta-glucuronidase activity. This decreases net glucuronide formation by the liver. In support of this hypothesis, rates of glucuronide production were unaffected by epinephrine in perfused livers from beta-glucuronidase-deficient C3H/HeJ mice.

Animals↗
PubMed1984

p-Nitroanisole O-demethylation in perfused hamster liver. High rates of pentose cycle-independent mixed-function oxidation.

Rates of p-nitroanisole O-demethylation in perfused livers from Syrian golden hamsters were three to four times greater than comparable rates measured in preparations from Sprague-Dawley rats. Hamsters also had greater microsomal p-nitroanisole O-demethylase activity and cytochrome P-450 contents than rats. In general, phenobarbital caused similar increases in these properties in both species. Fasting of hamsters for 24 hr increased p-nitroanisole O-demethylase activity in microsomes but did not affect rates in perfused livers. Rates were also unaffected in the perfused liver by pretreatment with 6-aminonicotinamide, an inhibitor of the pentose phosphate shunt. Hamster livers had low activities of pentose cycle enzymes but high activities of malic enzyme and isocitrate dehydrogenase compared to rats. In hamster livers, maximal rates of p-nitroanisole O-demethylation were not maintained but declined steadily over 40 min with prolonged p-nitroanisole infusion. The decreased rates of mixed-function oxidation in the non-recirculating perfusion system could not be explained by diminished tissue viability or degradation of cytochrome P-450 but were likely due to a decline in the formation of reduced cofactor. Hepatic concentrations of alpha-ketoglutarate and malate increased during p-nitroanisole infusion. Furthermore, rates of p-nitroanisole O-demethylation were inhibited by ethanol and aminooxyacetate, agents which inhibit the generation and/or movement of mitochondrial reducing equivalents into the cytosol. The infusion of pyruvate stimulated p-nitroanisole O-demethylation in perfused livers from fasted hamsters. This effect was maximal with 0.1 mM pyruvate, did not require gluconeogenesis, and was insensitive to 6-aminonicotinamide treatment. Thus, stimulation of p-nitroanisole metabolism by pyruvate in hamster livers is likely related to the mitochondrial oxidation of pyruvate, rather than to increased NADPH generation via the pentose phosphate cycle. These data indicate that mitochondrial sources of NADPH supply reducing equivalents for mixed-function oxidation in hamster liver.

Aminooxyacetic Acid↗
PubMed1984

Reducing equivalents for mixed function oxidation in periportal and pericentral regions of the liver lobule in perfused livers from normal and phenobarbital-treated rats.

The supply of NADPH for cytochrome P-450-dependent mixed function oxidation from the pentose cycle and mitochondria in periportal and pericentral regions of the liver lobule was evaluated in perfused rat liver. Rates of 7-ethoxycoumarin O-deethylation in livers from fed, normal rats monitored with micro-light guides placed on periportal and pericentral regions were 1.2 mumol/g/hr in both regions of the liver lobule. In livers from fed, phenobarbital-treated rats, rates were 3.6 and 7.0 mumol/g/hr in periportal and pericentral regions, respectively. Following treatment of rats with 6-aminonicotinamide, an inhibitor of the pentose cycle, rates of 7-hydroxycoumarin production were approximately 0.9 mumol/g/hr in both regions of the lobule in livers from normal rats and 2.1 and 3.4 mumol/g/hr in periportal and pericentral regions, respectively, in livers from phenobarbital-treated rats. Based on the difference in rates of 7-hydroxycoumarin production in the presence and absence of 6-aminonicotinamide, we conclude that the pentose cycle supplies NADPH for 7-ethoxycoumarin metabolism at rates around 0.3 mumol/g/hr in both regions of the liver lobule in livers from normal rats and 1.5 and 3.6 mumol/g/hr in periportal and pericentral regions, respectively, in livers from phenobarbital-treated rats. Potassium cyanide, an inhibitor of mitochondrial oxidation, reduced rates of 7-ethoxycoumarin O-deethylation to approximately 0.6 mumol/g/hr in both regions of the liver lobule in livers from fed, normal rats and to around 0.2 mumol/g/hr after fasting or treatment with 6-aminonicotinamide. In livers from fasted, phenobarbital-treated rats, 7-hydroxycoumarin was produced at rates of 0.3 and 0.7 mumol/g/hr in periportal and pericentral regions, respectively, in the presence of KCN. Decreases in rates of 7-hydroxycoumarin production during KCN infusion indicate that the mitochondria supply about 0.7 mumol of NADPH/g/hr for 7-ethoxycoumarin metabolism in both regions in livers from normal rats and 1.3 and 2.7 mumol/g/hr in periportal and pericentral regions in livers from phenobarbital-treated rats. The sum of KCN and 6-aminonicotinamide-sensitive rates of 7-ethoxycoumarin metabolism closely approximated rates measured in the absence of the inhibitors. These data indicate that mitochondria supply 50 to 70% of the reducing equivalents for mixed function oxidation of 7-ethoxycoumarin in both regions of the liver lobule in livers from fed rats.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1984

Trypan blue uptake as a new method to investigate hepatotoxicity in periportal and pericentral regions of the liver lobule: studies with allyl alcohol in the perfused liver.

A new method based on trypan blue uptake was developed to study zonal hepatotoxicity in specific regions of the liver lobule in perfused livers. Allyl alcohol (350 microM), a hepatotoxin that causes necrosis of periportal regions, was infused into livers from phenobarbital-treated rats for 60 min. The subsequent infusion of trypan blue (0.2 mM) stained nuclei in periportal but not midzonal or pericentral regions of the liver lobule. With this new method of dye uptake, comparison of the temporal relationship between metabolic changes and the onset of cellular damage was possible. During the first 10 min of allyl alcohol infusion, allyl alcohol was taken up at rates of 64 mumol/g/h concomitant with an increase in oxygen uptake of 18 mumol/g/h. Allyl alcohol infusion also increased bile flow from 69 to 167 microliters/min and release of oxidized glutathione from 127 to 217 nmol/g/h, respectively. However, during the next 20-min phase of exposure to allyl alcohol, oxygen uptake was inhibited by 60% and allyl alcohol uptake declined by 80%. Bile flow and release of oxidized glutathione also declined continuously between 10 and 30 min and by 30 min stopped completely. Concomitant with the inhibition of oxygen uptake, rates of glycogenolysis and glycolysis increased by 130 and 85%, respectively. Within minutes after maximal inhibition of oxygen uptake, between 30 and 40 min after initiation of allyl alcohol infusion, trypan blue was taken up by hepatocytes in periportal zones of the liver lobule. Subsequently, lactate dehydrogenase began to appear in the effluent perfusate.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Propanol↗
PubMed1984

Rates of allyl alcohol metabolism in periportal and pericentral regions of the liver lobule.

Rates of allyl alcohol metabolism in periportal and pericentral regions of the liver lobule were measured to determine whether the zonal toxicity due to allyl alcohol results from its selective metabolism in periportal regions. Infusion of allyl alcohol into perfused livers from fed, phenobarbital-treated rats caused an increase in NADH fluorescence (366 leads to 450 nm) measured with a large-tipped (2-mm) light guide placed on the surface of the liver. A linear increase in NADH fluorescence was observed when 25-150 microM allyl alcohol was infused; however, when allyl alcohol exceeded 200 microM, oxygen uptake by the liver was inhibited 30-40%, and a large increase in NADH fluorescence occurred. Miniature oxygen electrodes were then placed on periportal and pericentral regions of the liver lobule and local rates of oxygen uptake were determined [Matsumura and Thurman, Am. J. Physiol. 244:G656-G659 (1983)]. Allyl alcohol (350 microM) or acrolein (200 microM) inhibited oxygen uptake only in periportal regions. Micro-light guides were placed on periportal and pericentral regions of livers perfused in either the anterograde or retrograde direction. The maximal increase in NADH fluorescence due to allyl alcohol infusion (100 microM) was greater in pericentral than in periportal regions. 4-Methylpyrazole (80 microM), an inhibitor of alcohol dehydrogenase, prevented the fluorescence increase due to allyl alcohol in both regions, indicating that the changes were due entirely to NADH generated from alcohol dehydrogenase-dependent allyl alcohol metabolism. Using the correlation (r = 0.91) between rates of allyl alcohol uptake and the increase in NADH fluorescence established for the whole organ, local rates of allyl alcohol metabolism were 23 and 31 mumoles/g/hr in periportal and pericentral regions, respectively. These results indicate that metabolism of allyl alcohol occurs at slightly greater rates in pericentral than in periportal regions of the liver lobule. Thirty minutes after the i.p. injection of a necrogenic dose of allyl alcohol in vivo, the concentrations of allyl alcohol in the portal vein and vena cava were 1210 and 530 microM, respectively. Thus, both periportal and pericentral regions of the liver lobule were exposed to concentrations of allyl alcohol (e.g., greater than 200 microM) which were metabolized in the perfused liver. Since allyl alcohol is metabolized in both regions of the liver lobule, the hypothesis that the zone-specific hepatotoxicity results from its exclusive metabolism to acrolein in periportal regions seems unlikely.

1-Propanol↗
PubMed1983

Stimulation of mixed-function oxidation of 7-ethoxycoumarin in periportal and pericentral regions of the perfused rat liver by xylitol.

Rates of O-deethylation of 7-ethoxycoumarin by perfused livers from fasted, phenobarbital-treated rats were 3.7 mumol X g-1 X h-1. Approximately 50% of the product was conjugated. When rates of 7-ethoxycoumarin O-deethylation were varied by infusing different concentrations of substrate, a good correlation (r = 0.91) was found between rates of O-deethylation of 7-ethoxycoumarin and fluorescence of 7-hydroxycoumarin detected from the liver surface. Micro-light guides (tip diameter 170 microns) placed on periportal and pericentral regions on the liver surface were used to monitor the conversion of nonfluorescent 7-ethoxycoumarin to fluorescent 7-hydroxycoumarin. The O-deethylation of 7-ethoxycoumarin to 7-hydroxycoumarin increased fluorescence 64% and 28% in pericentral and periportal regions of the liver lobule, respectively. Rates of 7-ethoxycoumarin O-deethylation estimated from these increases in fluorescence were 5.2 mumol X g-1 X h-1 in pericentral and 2.2 mumol X g-1 X h-1 in periportal regions of the liver. During mixed-function oxidation of 7-ethoxycoumarin, the oxidation:reduction state of NADP(H) was similar in both regions of the liver lobule. Xylitol (2 mM) decreased the NADP+/NADPH ratio and stimulated rates of drug metabolism in both regions of the liver lobule. This indicates that conditions exist where the supply of NADPH is an important rate-determining factor for 7-ethoxycoumarin metabolism in both periportal and pericentral regions of the liver lobule.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1983

Inhibition of p-nitroanisole O-demethylation in perfused rat liver by potassium cyanide.

The effect of potassium cyanide on p-nitroanisole O-demethylation in perfused rat livers has been examined. Cyanide (2 mM), an inhibitor of cytochrome oxidase, diminished p-nitroanisole O-demethylation by 50-75% in perfused livers from normal and phenobarbital-treated rats, but had much less effect on hepatic microsomal p-nitroanisole O-demethylation. The inhibition was also observed in livers where the activity of the pentose phosphate shunt was abolished by pretreatment with 6-aminonicotinamide. Cyanide infusion decreased hepatic ATP/ADP ratios and cellular concentrations of glutamate, alpha-ketoglutarate, and isocitrate, but caused an increase in the NADP+/NADPH ratio. Rates of NADPH generation via the pentose phosphate shunt were unchanged by cyanide, and hepatic concentrations of glucose 6-phosphate were markedly increased by cyanide. Thus, inhibition of p-nitroanisole metabolism could not be explained solely by a direct interaction of cyanide with mixed-function oxidases or diminished NADPH generation via the pentose cycle. These data indicate that cyanide inhibits mixed-function oxidation in intact cells by diminishing the generation of NADPH from sources other than the pentose cycle. Further, these data are consistent with the hypothesis that some NADPH for mixed-function oxidation arises from cyanide-sensitive mitochondrial sources.

Animals↗
PubMed1983

Effects of ethanol and sorbitol on mixed-function oxidation in perfused rat livers.

Ethanol (20 mM) caused 50-90% inhibition of rates of mixed-function oxidation of p-nitroanisole, 7-ethoxycoumarin and benzo(a)pyrene in perfused rat livers; however, the microsomal metabolism of these substrates was unaltered by low concentrations of ethanol. The metabolism of ethanol was required for this inhibition in the perfused liver. In contrast to ethanol, sorbitol stimulated rates of p-nitroanisole O-demethylation in perfused livers from fasted, phenobarbital-treated rats. Both sorbitol and ethanol infusion decreased the hepatic NAD+/NADH ratio; however, the NADP+/NADPH ratio was decreased by sorbitol but increased by ethanol. Stimulation of drug metabolism by sorbitol was abolished by pretreatment of fasted rats with 6-aminonicotinamide, an inhibitor of the pentose phosphate shunt. These data indicated that sorbitol stimulated p-nitroanisole metabolism by providing NADPH via the pentose phosphate shunt. The changes in intracellular concentrations of NADPH produced by ethanol and sorbitol correlated directly with changes in hepatic content of citrate and aspartate. These data suggest that inhibition of the citric acid cycle by ethanol decreases the movement of mitochondrial reducing equivalents into the cytosol via substrate shuttle mechanisms.

Acetaldehyde↗
PubMed1983

Metabolic heterogeneity in the perfused rat liver.

New methods have been developed to monitor metabolic events non-invasively within periportal and pericentral regions of perfused rat livers. These techniques utilize two-fiber micro-light guides and miniature oxygen electrodes positioned on identified lobular regions of the perfused liver based on differential pigmentation of periportal and pericentral areas. Two-fiber micro-light guides detect the fluorescence of native and introduced fluors and are used to monitor redox changes of endogenous pyridine nucleotides and the generation of fluorescent products (e.g., 7-hydroxycoumarin) from exogenous substrates. Changes in fluorescence detected with two-fiber micro-light guides are correlated with changes measured with large, multi-fiber light guides and with whole organ rates of metabolism. Subsequently, local rates are estimated. With these techniques, we show that (a) rates of ethanol and acetaldehyde metabolism are similar in periportal and pericentral regions of the liver lobule; (b) mixed-function oxidation predominantes in pericentral regions in livers from phenobarbital-treated rats; (c) rates of sulfation of 7-hydroxycoumarin are greater in periportal than in pericentral hepatocytes; and (d) oxygen uptake is approximately 3-fold greater in periportal than in pericentral areas of the liver lobule.

Acetaldehyde↗
PubMed1982

Regulation of NADPH-dependent mixed-function oxidation in perfused livers. Comparative studies with sorbitol and ethanol.

Sorbitol and ethanol were shown to have opposite effects on p-nitroanisole O-demethylation in perfused livers from fasted, phenobarbital-treated rats. Sorbitol (2 mM) stimulated drug metabolism by 50% while ethanol (20 mM) caused 80% inhibition. Both sorbitol and ethanol infusion decreased the NAD+/NADH ratio and increased fluorescence of pyridine nucleotides monitored from the liver surface; however, the NADP+/NADPH ratio was decreased by sorbitol but tended to be increased by ethanol. Stimulation of drug metabolism by sorbitol was abolished by pretreatment of fasted rats with 6-aminonicotinamide, an inhibitor of the pentose phosphate shunt, but was not affected by aminooxyacetate, a transaminase inhibitor. These results indicate that sorbitol stimulated p-nitroanisole metabolism by providing NADPH via the pentose phosphate shunt. Ethanol and sorbitol caused changes in intracellular concentrations of NADPH in livers from fasted rats which correlated directly with changes in hepatic levels of citrate and aspartate. Furthermore, aspartate infusion reduced the inhibition of p-nitroanisole O-demethylation by ethanol. This inhibition was also reversed partially by sorbitol in livers from 6-aminonicotinamide-treated rats. It is concluded that ethanol inhibits mixed-function oxidation primarily by decreasing the concentrations of citric acid cycle intermediates which leads to depletion of cytosolic NADPH.

Animals↗
PubMed1982

Effect of chronic ethanol diet on the replication, alkylation, and repair of DNA from hepatocytes and nonparenchymal cells following dimethylnitrosamine administration.

Chronic alcohol ingestion has been associated with human cancer of the larynx, esophagus, and liver, however the mechanism(s) of ethanol's interaction in either initiation and/or progression of cancer is unknown. The initiation of chemical carcinogenesis is thought to involve an alteration of the DNA which becomes fixed in the daughter strand following the replication of DNA containing promutagenic damage. The purpose of this study was to investigate the effects of a chronic ethanol diet and acute dimethylnitrosamine administration on the replication, alkylation, and repair of DNA from nonparenchymal cells and hepatocytes of rat liver. DNA replication of nonparenchymal cells, but not hepatocytes, was inhibited in animals on the chronic ethanol diet. Dimethylnitrosamine exposure reversed this inhibitory effect 24 h after exposure. Hepatocyte alkylation and repair of DNA following dimethylnitrosamine administration was unaffected by the ethanol diet. 7-Methylguanine was lost from both cell populations equally during a 72 h time course. In contrast, O6-methylguanine was removed much more efficiently in hepatocytes. The nonparenchymal cells had 10 times more O6-methylguanine than hepatocytes 72 h after dimethylnitrosamine administration. Lower concentrations of 7-methylguanine and O6-methylguanine were present in nonparenchymal cells of ethanol treated rats compared to controls. Although in vitro studies have demonstrated increased microsomal activation and mutagenesis of dimethylnitrosamine following chronic ethanol ingestion, the present study demonstrates that in vivo metabolism of dimethylnitrosamine resulting in DNA alkylation is not increased by chronic ethanol exposure.

Alkylation↗