Overexpression of a monomeric form of the bovine odorant-binding protein protects Escherichia coli from chemical-induced oxidative stress

Mammalian odorant-binding proteins (OBPs) are soluble lipocalins produced in the nasal mucosa and in other epithelial tissues of several animal species, where they are supposed to serve as scavengers for small structurally unrelated hydrophobic molecules. These would include odorants and toxic aldehydes like 4-hydroxy-2-nonenal (HNE), which are end products of lipid peroxidation; therefore OBP might physiologically contribute to preserve the integrity of epithelial tissues under oxidative stress conditions by removing toxic compounds from the environment and, eventually, driving them to the appropriate degradative pathways. With the aim of developing a biological model based on a living organism for the investigation of the antioxidant properties of OBP, here we asked whether the overexpression of the protein could confer protection from chemical-induced oxidative stress in Escherichia coli. To this aim, bacteria were made to overexpress either GCC-bOBP, a redesigned monomeric mutant of bovine OBP, or its amino-terminal 6-histidine-tagged version 6H-GCC-bOBP. After inducing overexpression for 4 h, bacterial cells were diluted in fresh culture media, and their growth curves were followed in the presence of hydrogen peroxide (H2O2) and tert-Butyl hydroperoxide (tBuOOH), two reactive oxygen species whose toxicity is mainly due to lipid peroxidation, and menadione, a redox-cycling drug producing the superoxide ion. GCC-bOBP and 6H-GCC-bOBP were found to protect bacterial cells from the insulting agents H2O2 and tBuOOH but not from menadione. The obtained data led us to hypothesize that the presence of overexpressed OBP may contribute to protect bacterial cells against oxidative stress probably by sequestering toxic compounds locally produced during the first replication cycles by lipid peroxidation, before bacteria activate their appropriate enzyme-based antioxidative mechanisms.

α(1D)-Adrenoceptor regulates the vasopressor action of α(1A)-adrenoceptor in mesenteric vascular bed of α(1D)-adrenoceptor knockout mice

1 The pressor action of the α(1A)-adrenoceptor (α(1A)-AR) agonist A61603 (N-[5-(4,5-dihydro-1H-imidazol-2-yl)-2-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl] methanesulfonamide) and the α(1)-ARs agonist phenylephrine and their blockade by selective α(1)-ARs antagonists in the isolated mesenteric vascular bed of wild-type (WT) mice and α(1D)-AR knockout (KO α(1D)-AR) mice were evaluated. 2 The apparent potency of A61603 to increase the perfusion pressure in the mesenteric vascular bed of WT and KO α(1D)-AR mice is 86 and 138 times the affinity of phenylephrine, respectively. 3 A61603 also enhanced the perfusion pressure by ≈1.7 fold in the mesenteric vascular bed of WT mice compared with KO α(1D)-AR mice. 4 Because of its high affinity, low concentrations of the α(1A)-AR selective antagonist RS100329 (5-methyl-3-[3-[4-[2-(2,2,2,-trifluoroethoxy) phenyl]-1-piperazinyl] propyl]-2,4-(1H)-pyrimidinedione) shifted the agonist concentration-response curves to the right in the mesenteric vascular bed of WT and KO α(1D)-AR mice. 5 The α(1D)-AR selective antagonist BMY7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5] decane-7,9-dione) did not modify the A61603 or the phenylephrine-induced pressor effect. 6 The α(1B/D)-ARs alkylating antagonist chloroethylclonidine (CEC) shifted the agonist concentration-response curves to the right and decreased the maximum phenylephrine-induced vascular contraction in KO α(1D)-AR mice when compared to WT mice; however, CEC only slightly modified the contraction induced by A61603. 7 The results indicate that the isolated mesenteric vascular bed of WT and KO α(1D)-AR mice expresses α(1A)-AR, that the pressor action of α(1A)-AR is up-regulated for α(1D)-AR in WT mice and suggest an important role of α(1B)-AR in the vascular pressure evoked by phenylephrine in KO α(1D)-AR mice.

Aromatic hydrocarbons upregulate glyceraldehyde-3-phosphate dehydrogenase and induce changes in actin cytoskeleton. Role of the aryl hydrocarbon receptor (AhR)

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional enzyme involved in several cellular functions including glycolysis, membrane transport, microtubule assembly, DNA replication and repair, nuclear RNA export, apoptosis, and the detection of nitric oxide stress. Therefore, modifications in the regulatory ability and function of GAPDH may alter cellular homeostasis. We report here that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and beta-naphthoflavone, which are well-known ligands for the aryl hydrocarbon receptor (AhR), increase GAPDH mRNA levels in vivo and in vitro, respectively. These compounds fail to induce GAPDH transcription in an AhR-null mouse model, suggesting that the increase in GAPDH level is dependent upon AhR activation. To analyse the consequences of AhR ligands on GAPDH function, mice were treated with TCDD and the level of liver activity of GAPDH was determined. The results showed that TCDD treatment increased GAPDH activity. On the other hand, treatment of Hepa-1 cells with beta-naphthoflavone leads to an increase in microfilament density when compared to untreated cultures. Collectively, these results suggest that AhR ligands, such as polycyclic hydrocarbons, can modify GAPDH expression and, therefore, have the potential to alter the multiple functions of this enzyme.

Correlation between blood adenosine metabolism and sleep in humans

Blood adenosine metabolism, including metabolites and metabolizing enzymes, was studied during the sleep period in human volunteers. Searching for significant correlations among biochemical parameters found: adenosine with state 1 of slow-wave sleep (SWS); activity of 5'-nucleotidase with state 2 of SWS; inosine and AMP with state 3-4 of SWS; and activity of 5'-nucleotidase and lactate with REM sleep. The correlations were detected in all of the subjects that presented normal hypnograms, but not in those who had fragmented sleep the night of the experiment. The data demonstrate that it is possible to obtain information of complex brain operations such as sleep by measuring biochemical parameters in blood. The results strengthen the notion of a role played by adenosine, its metabolites and metabolizing enzymes, during each of the stages that constitute the sleep process in humans.

Adenosine reverses a preestablished CCl4-induced micronodular cirrhosis through enhancing collagenolytic activity and stimulating hepatocyte cell proliferation in rats

Cirrhosis is one of the most common causes of mortality worldwide, because hepatic dysfunction constitutes a potentially lethal condition. Having demonstrated the hepatoprotective effect of adenosine against CCl(4)-induced cirrhosis, the present study was aimed at assessing adenosine's effect on an already-established micronodular cirrhosis. Chronic administration of CCl(4) (10 weeks) induced a cirrhotic state, characterized by increased liver fibronectin and collagen types I and III content, enhanced expression of alpha-1 (I) collagen mRNA, portal hypertension, and liver dysfunction. After CCl(4) discontinuation (5 weeks), increased persitance of alpha-1 (I) collagen mRNA expression and deposition, enhanced proline incorporation into collagen and prolyl hydroxylase activity evidenced active fibrogenesis. Several weeks after CCl(4) withdrawal, deposited collagen showed an enhanced type I/III ratio, which was associated with deficient collagenolytic activity in cirrhotic livers. Liver expression of some metalloproteinases (MMPs) and of tissue inhibitors of MMPs (TIMPs) also indicated decreased collagen breakdown in cirrhotic livers. Parameters indicative of oxidative stress (mainly protein oxidation) were persistently augmented. These events were coincident with diminished regenerative capacity of the cirrhotic liver. Intraperitoneal adenosine administration to CCl(4)-induced cirrhotic rats blocked active fibrogenesis and increased the collagen degradation (most probably by decreasing liver TIMPs levels), normalizing collagen-type ratios. In addition, the nucleoside promoted an effective hepatocyte's proliferation in the cirrhotic liver and accelerated normalization of parameters indicative of liver function and oxidative stress. Thus, adenosine readily reversed an experimental cirrhosis through stimulating liver collagenolytic and proliferative capacities, as well as by accelerating functional recovery.

Effects of ethanol administration on hepatocellular ultrastructure of regenerating liver induced by partial hepatectomy

Acute ethanol administration partially inhibits DNA and protein syntheses during liver regeneration (LR) induced by partial hepatectomy (PH) in rats. Previous findings that the magnitude of ethanol's deleterious effects on LR are related to the route and timing of its administration led us to perform studies at the ultrastructural level, comparing ethanol effects on PH-induced LR, as a consequence of its administration route. PH promoted alterations on the endoplasmic reticulum and mitochondria, accompanied by decreased glycogen and increased lipid content in cytoplasm. Structural nuclear and nucleolar activities were also evident. Intragastric ethanol administration practically abolished the adaptative changes found in PH-promoted regenerating hepatocytes, whereas its administration through the intraperitoneal route induced later ultrastructural modifications, indicating cellular proliferation. These results suggest that ethanol, under certain conditions, could stimulate liver proliferation triggered by PH. The mechanism underlying this surprising effect of ethanol on LR remains to be elucidated. However, it is suggested that an altered ethanol metabolism by rats subjected to PH could be involved.

Gastric mucosal cell proliferation in ethanol-induced chronic mucosal injury is related to oxidative stress and lipid peroxidation in rats

The oxygen free radicals-induced lipid peroxidation (LP) has been implicated in the pathogenesis of acute ethanol-induced gastric mucosal lesions. However, the role of LP in the generation of chronic gastric mucosal injury is unknown. We have developed a model of chronic mucosal injury induced by continuous ethanol ingestion for 5 days and characterized by marked alterations in plasma membranes from gastric mucosa. Therefore, LP was evaluated in this experimental model. Indicators of peroxidative activity, mucosal glutathione content, thymidine kinase activity (an index of cell proliferation), and histamine H2-receptor (H2R) binding constants were quantified in animals undergoing gastric mucosal damage. The effect of famotidine, a H2R antagonist that readily ameliorates the chronic mucosal injury, was also tested. Increased free radicals and LP levels were detected during gastritis; however, a second, higher peak of LP was noted in mucosal plasma membranes after ethanol withdrawal (recovery period). This further increase of LP coincided with active cell proliferation, decreased mucosal glutathione levels, and diminished specific cimetidine binding by H2R. Administration of famotidine accelerated the mucosal proliferative process, inducing the second lipoperoxidative episode sooner, and preserved the content of glutathione. In addition, LP correlated directly with cell proliferation and inversely with mucosal membrane cimetidine binding. In conclusion, LP seems to be involved in chronic ethanol-induced gastric mucosal injury. However, a further enhancement of plasma membrane LP occurred, associated with increased DNA synthesis and diminished cimetidine binding by membrane H2R. Therefore, increased LP could also participate in the compensatory mucosal proliferation initiated after ethanol withdrawal.

Redox state and energy metabolism during liver regeneration: alterations produced by acute ethanol administration

Ethanol metabolism can induce modifications in liver metabolic pathways that are tightly regulated through the availability of cellular energy and through the redox state. Since partial hepatectomy (PH)-induced liver proliferation requires an oversupply of energy for enhanced syntheses of DNA and proteins, the present study was aimed at evaluating the effect of acute ethanol administration on the PH-induced changes in cellular redox and energy potentials. Ethanol (5 g/kg body weight) was administered to control rats and to two-thirds hepatectomized rats. Quantitation of the liver content of lactate, pyruvate, beta-hydroxybutyrate, acetoacetate, and adenine nucleotides led us to estimate the cytosolic and mitochondrial redox potentials and energy parameters. Specific activities in the liver of alcohol-metabolizing enzymes also were measured in these animals. Liver regeneration had no effect on cellular energy availability, but induced a more reduced cytosolic redox state accompanied by an oxidized mitochondrial redox state during the first 48 hr of treatment; the redox state normalized thereafter. Administration of ethanol did not modify energy parameters in PH rats, but this hepatotoxin readily blocked the PH-induced changes in the cellular redox state. In addition, proliferating liver promoted decreases in the activity of alcohol dehydrogenase (ADH) and of cytochrome P4502E1 (CYP2E1); ethanol treatment prevented the PH-induced diminution of ADH activity. In summary, our data suggest that ethanol could minimize the PH-promoted metabolic adjustments mediated by redox reactions, probably leading to an ineffective preparatory event that culminates in compensatory liver growth after PH in the rat.

Morphological and biochemical effects of a low ethanol dose on rat liver regeneration: role of route and timing of administration

We have demonstrated that in rats subjected to partial hepatectomy (PH), the regenerating liver had an enhanced metabolism of ethanol, which largely depended on the route and timing of ethanol administration. Therefore, the influence of the administration route and timing for ethanol-induced deleterious effects on the regenerating rat liver was evaluated in animals subjected to 70% PH. Remnant liver showed moderate fatty infiltration, extended distortion of hepatocellular structure, and high mitotic index. Intragastric ethanol administration (1.5 g/kg body weight) considerably reduced the PH-induced changes in liver structures. Ethanol treatment also decreased liver thymidine kinase activity, serum albumin, and glucose levels. Intraperitoneal administration of the same ethanol dose to PH rats promoted lesser alterations on liver regeneration. Independently of its administration route, ethanol abruptly shortened a PH-induced selective increase in serum enzyme activities. These data suggest that the inhibitory effect of a low dose of ethanol on PH-induced liver regeneration is dependent on the timing and route of administration.

Pharmacokinetics of the ethanol bioavailability in the regenerating rat liver induced by partial hepatectomy

It is well known that a single ethanol administration is capable of inhibiting the two-thirds partial hepatectomy (PH)-induced liver regeneration (LR); nonetheless, it has not been elucidated how ethanol metabolism by the remnant liver is exerting the deleterious ethanol actions on LR. Indeed, pharmacokinetics analysis of ethanol elimination is lacking in rats subjected to PH, which might extend our understanding in the mechanisms that account for the ethanol-induced inhibition on LR after PH in the rat. Therefore, the present study is a pharmacokinetics analysis comparing intragastric and intraperitoneal administrations of ethanol to rats under PH, at several times after surgery (0 to 96 hr postsurgery). Our results show that PH rats had a much lower blood ethanol peak than sham-operated, when intragastrically administered during the first 4 hr after surgery that was transient and normalized at 6 hr post-PH. The area under the curve for blood ethanol was higher in PH animals, starting after 6 hr postsurgery and extended to the all replicative period, and returned within the control values thereafter. The quantity of ethanol absorbed after its intraperitoneal injection was essentially the same as the administered dose for all of the groups tested. Hence, ethanol bioavailability diminished due to an enhanced rate of the first-pass metabolism for ethanol in PH rats at the very early times post-PH. At later times of PH, ethanol bioavailability was practically normalized, and these effects were accompanied by a drastic increase in the liver capacity to metabolize ethanol, mainly at 48 to 96 hr after surgery, as calculated as ethanol elimination per gram of liver, as well as by total body weight. The very early changes in ethanol bioavailability in PH rats were not accounted for gastric ethanol retention in these animals. In conclusion, first-pass metabolism importantly participates in the modified ethanol bioavailability at very early times after PH, an event presumably attained to gastric catabolism of ethanol. However, the very enhanced metabolism of ethanol showed by the regenerating liver, particularly after the first 24 hr postsurgery, seems to be the main factor affecting ethanol pharmacokinetics in rats subjected to PH. The underlying mechanisms in this liver enhancement of ethanol oxidation by PH rats remains to be elucidated.

Changes in the redox state in the retina and brain during the onset of diabetes in rats

Diabetic retinopathy is thought to result from chronic changes in the metabolic pathways of the retina. Hyperglycemia leads to increased intracellular glucose concentrations, alterations in glucose degradation and an increase in lactate/pyruvate ratio. We measured lactate content in retina and other ocular and non-ocular tissues from normal and diabetic rats in the early stages of streptozotocin-induced diabetes. The intracellular redox state was calculated from the cytoplasmic [lactate]/[pyruvate] ratio. Elevated lactate concentration were found in retina and cerebral cortex from diabetic rats. These concentrations led to a significant and progressive decrease in the NAD+/NADH ratio, suggesting that altered glucose metabolism is an initial step of retinopathy. It is thus possible that tissues such as cerebral cortex have mechanisms that prevent the damaging effect of lactate produced by hyperglycemia and/or alterations of the intracellular redox state.

Modifications of intracellular calcium release channels and calcium mobilization following 70% hepatectomy

The aim of this study was to investigate the properties of ryanodine and IP3 receptors in regenerating liver following 70% hepatectomy, and to evaluate the hepatic Ca2+ distribution and mobilization during this process. Specific [3H]ryanodine and [3H]IP3 binding to hepatic smooth endoplasmic reticulum membranes, as well as subcellular Ca2+ determination by atomic absorption flame photometry and Ca2+ mobilization by INDO-1 AM spectrofluorescence in hepatocytes, was performed in regenerating livers after surgical 70% hepatectomy. Incorporation of 14C amino acids into proteins and of 32P into phospholipids was done in subcellular fractions. Ryanodine receptor Kd presented a dramatic increase after 12 h of surgery and remained high up to 2 days of treatment. IP3 receptor Bmax showed a significant augmentation starting at 6 h after hepatectomy and returning to normal values after 1 week. Cytosolic total calcium content decreased from 12 h until 4 days after hepatectomy whereas the microsomal and mitochondrial total calcium increased at 1 and 2-4 days of liver regeneration, which coincided with the differential turnover of proteins and phospholipids in these fractions. ATP-induced Ca2+ transients in hepatocytes of 24-h-hepatectomized rats confirmed the altered sensitivity of the ryanodine receptor toward its ligand, since 10 times more ryanodine was necessary to alter the ATP-induced Ca2+ transient. The data support the notion that the calcium release channels are targets of mechanisms of metabolic control during the proliferative response following 70% hepatectomy and might be part of the modified intracellular Ca2+ dynamics during liver regeneration.

Sequential changes of energy metabolism and mitochondrial function in myocardial infarction induced by isoproterenol in rats: a long-term and integrative study

Acute myocardial infarction is the second cause of mortality in most countries, therefore, it is important to know the evolution and sequence of the physiological and biochemical changes involved in this pathology. This study attempts to integrate these changes and to correlate them in a long-term model (96 h) of isoproterenol-induced myocardial cell damage in the rat. We achieved an infarct-like damage in the apex region of the left ventricle, occurring 12-24 h after isoproterenol administration. The lesion was defined by histological criteria, continuous telemetric ECG recordings, and the increase in serum marker enzymes, specific for myocardial damage. A distinction is made among preinfarction, infarction, and postinfarction. Three minutes after drug administration, there was a 60% increase in heart rate and a lowering of blood pressure, resulting possibly in a functional ischemia. Ultrastructural changes and mitochondrial swelling were evident from the first hour of treatment, but functional alterations in isolated mitochondria, such as decreases in oxygen consumption, respiratory quotient, ATP synthesis, and membrane potential, were noticed only 6 h after drug administration and lasted until 72 h later. Mitochondrial proteins decreased after 3 h of treatment, reaching almost a 50% diminution, which was maintained during the whole study. An energy imbalance, reflected by a decrease in energy charge and in the creatine phosphate/creatine ratio, was observed after 30 min of treatment; however, ATP and total adenine nucleotides diminished clearly only after 3 h of treatment. All these alterations reached a maximum at the onset of infarction and were accompanied by damage to the myocardial function, drastically decreasing left ventricular pressure and shortening the atrioventricular interval. During postinfarction, a partial recovery of energy charge, creatine phosphate/creatine ratio, membrane potential, and myocardial function occurred, but not of mitochondrial oxygen consumption, rate of ATP synthesis, total adenine nucleotides, or mitochondrial proteins. Interesting correlations of the sequential changes in heart and mitochondrial functions with energy metabolism were obtained at different stages of the isoproterenol-induced cardiotoxicity. These correlations could be useful to study and understand the cellular events involved in this pathology.

Balance between oxidative damage and proliferative potential in an experimental rat model of CCl4-induced cirrhosis: protective role of adenosine administration

Oxidative stress and its consequent lipid peroxidation (LP) exert harmful effects, which have been currently involved in the generation of carbon tetrachloride-induced cirrhosis. However, the recent report that "physiological" LP can be associated with liver regeneration (LR) makes it necessary to discriminate between oxidative stress-induced and LR-associated LP. In rats rendered cirrhotic by continuous CCl4 administration for 4 weeks, moderate cell necrosis and fine fatty infiltration were found. The histological abnormalities were accompanied by increased LP, mainly accounted for by the microsomal and cytosolic fractions and evidence of oxidative stress (decreased hepatic glutathione content and changes in xanthine oxidase and pentose phosphate pathway activities). After 8 weeks, a micronodular cirrhosis developed, but oxidative stress was greatly attenuated, only persisting in the enhanced LP confined to microsomes. Simultaneous administration of adenosine, a reliable hepatoprotector that readily prevents the onset of liver fibrosis, was able to block the oxidative stress induced by the long-term CCl4 treatment but elicited a selective subcellular distribution of increased LP, similar to that found during LR. The adenosine-induced changes in liver LP (mainly in the nuclear fraction) correlated with an increased activity of thymidine kinase. Therefore, data suggest that adenosine-mediated preservation of energy availability and mitochondrial function could participate in preventing the onset of oxidative stress in cirrhotic rats. The latter could induce a successful liver recovery, curtailing the sequence of events leading to fibrogenesis.

Purification of alcohol dehydrogenase from Entamoeba histolytica and Saccharomyces cerevisiae using zinc-affinity chromatography

We have developed a single-step method for the purification of NADP(+)-dependent alcohol dehydrogenase from Entamoeba histolytica and NAD(+)-dependent alcohol dehydrogenase from Saccharomyces cerevisiae. It is based on the affinity for zinc of both enzymes. The amebic enzyme was purified almost 800 times with a recovery of 54% and the yeast enzyme was purified 30 times with a recovery of 100%. The kinetic constants of the purified enzymes were similar to those reported for other purification methods. With mammalian alcohol dehydrogenase, we obtained a 40-kDa band suggestive of purified alcohol dehydrogenase, but we failed to retain enzymatic activity in this preparation. Our results suggest that the described method is more applicable to the purification of tetrameric alcohol dehydrogenases.

Reversion by histamine H2-receptor antagonists of plasma membrane alterations in ethanol-induced gastritis

Ethanol administration rapidly damages surface epithelial cells of rat stomach, leading to altered cellular plasma membranes. Histamine H2-receptor antagonists (H2RA) have been shown to have preventive properties against ethanol-induced gastric mucosal injury. Therefore, the possible reverting properties of H2RA (cimetidine, ranitidine, and famotidine) were tested in ethanol-induced gastritis. Subchronic ethanol administration elicited a histological profile of gastritis and alterations at the plasma membrane level (diminution of some phospholipids, increased cholesterol, and decreased activity of 5'-nucleotidase). H2RA administration to rats with gastritis promptly corrected the ethanol-induced mucosal damage. In addition, cytosolic enzyme activities (alcohol and lactate dehydrogenases) were also modified by gastritis and treatment with H2RA. In conclusion, our data suggest that H2RA improved restitution of the gastric mucosa contributing to the healing process of the gastric damage. The latter indicates reverting properties of H2RA on gastric damage, as well as their cytoprotective effect already described.

Selective enhancement of lipid peroxidation in plasma membrane in two experimental models of liver regeneration: partial hepatectomy and acute CC14 administration

It has been proposed that lipid peroxidation (LP) might be a modulator of cell division, influencing initiation and cessation of mitosis in regenerating liver. However, the understanding of the participating role of this event in the onset of liver proliferation has been hampered by the fact that both higher or lower LP have been reported after two-thirds partial hepatectomy (PH). Therefore, the present study deals with the extent of LP in the main subcellular fractions from rat liver at early stages of regeneration, induced by either PH of 70% or acute CCl4 administration. Our results, using several methods to monitor LP, indicate a differential effect in the peroxidative pattern of specific subcellular fractions from regenerating liver after 24 hours of PH: a decrease in microsomes and an increase confined to plasma membrane and cytosolic fractions, peaking after 24 hours of PH. In CCl4-treated rats, higher LP was also noted in plasma membrane and cytosol, being maximal at the replicative stage in this experimental model (48 hours). In addition, increased LP was found in microsomal and nuclear fractions, declining before the 48 hours. In hepatectomized rats, changes in LP seem to be an organ-specific event and related to only PHs capable of triggering a synchronized proliferative response, namely above 40%. These results show that LP, promoted by PH and CCl4 administration, is qualitatively distinct among subcellular fractions and may indeed be a normal cell event of physiological importance in the regenerating liver.

Sucrose administration to partially hepatectomized rats: a possible model to study ethanol-induced inhibition of liver regeneration

Although acute ethanol treatment drastically inhibits liver regeneration after partial hepatectomy, the exact mechanisms involved remain obscure. On the other hand, it is known that early carbohydrate administration promotes a more successful restoration of the liver mass. Therefore, carbohydrate administration could be an experimental approach for studying ethanol action on the regenerating liver. In rats subjected to two-thirds partial hepatectomy, ethanol was administered alone or in combination with a variety of carbohydrates (glucose, fructose, glucose plus fructose, sucrose and maltose). In liver samples, regeneration parameters and histological assessment were performed. Blood ethanol and metabolites reflecting liver function were assayed. Ethanol intake strongly decreased the incorporation of [3H]thymidine into liver DNA, the concentration of DNA/g of tissue, and thymidine kinase activity. In this group, severe alterations in cell structure (i.e. abundant fat droplets and abnormal mitochondria) were found. Carbohydrates readily improved the survival rate of ethanol-intoxicated hepatectomized rats. Sucrose was effective in reverting the ethanol-induced alterations in liver structure and the parameters of liver regeneration, and partially blocked the ethanol-induced alterations in serum levels of albumin, triacylglycerols and ammonia without modifying the blood levels and clearance of ethanol. Data suggest that the beneficial action of sucrose might be related to an adequate supply of energetic sources at early times of liver regeneration, rather than altering ethanol bioavailability. Thus, the present model could be an experimental approach for studying the metabolic alterations involved in the ethanol-induced inhibition of the liver regeneration.

Temporal variations of adenosine metabolism in human blood

Eight diurnally active (06:00-23:00 h) subjects were adapted for 2 days to the room conditions where the experiments were performed. Blood sampling for adenosine metabolites and metabolizing enzymes was done hourly during the activity span and every 30 min during sleep. The results showed that adenosine and its catabolites (inosine, hypoxanthine, and uric acid), adenosine synthesizing (S-adenosylhomocysteine hydrolase and 5'-nucleotidase), degrading (adenosine deaminase) and nucleotide-forming (adenosine kinase) enzymes as well as adenine nucleotides (AMP, ADP, and ATP) undergo statistically significant fluctuations (ANOVA) during the 24 h. However, energy charge was invariable. Glucose and lactate chronograms were determined as metabolic indicators. The same data analyzed by the chi-square periodogram and Fourier series indicated ultradian oscillatory periods for all the metabolites and enzymatic activities determined, and 24-h oscillatory components for inosine, hypoxanthine, adenine nucleotides, glucose, and the activities of SAH-hydrolase, 5'-nucleotidase, and adenosine kinase. The single cosinor method showed significant oscillatory components exclusively for lactate. As a whole, these results suggest that adenosine metabolism may play a role as a biological oscillator coordinating and/or modulating the energy homeostasis and physiological status of erythrocytes in vivo and could be an important factor in the distribution of purine rings for the rest of the organism.

Possible mechanism of adenosine protection in carbon tetrachloride acute hepatotoxicity. Role of adenosine by-products and glutathione peroxidase

Adenosine proved to be an effective hepatoprotector increasing the survival rate of rats receiving lethal doses of CCl4. Searching for the mechanism of action, we found that adenosine transiently prevents the necrotic liver damage associated to an acute CCl4 treatment. The antilipoperoxidative action of the nucleoside was evidenced by a decrease of TBA-reactive products and the diene conjugates elicited by the hepatotoxin. Adenosine's protective effect was demonstrated by reverting the decrease of cytochrome P-450 while preserved intact the activity of the microsomal enzyme glucose-6-phosphatase. CCl4 promoted an increase in the oxidant stress through an enhancement in oxidized glutathione levels. This action was also completely counteracted by the nucleoside. Adenosine was unable to prevent CCl4 activation and, even, increased .CCl3 formation in the presence of PBN in vivo. However, in the presence of the nucleoside, irreversible binding of 14CCl4 to the microsomal lipid fraction of the treated animals was decreased. These results suggest that adenosine protective action might be exerted at the level of the propagation reaction following CCl4 activation. Two possible mechanisms were associated to the nucleoside protection: (1) the peroxide-metabolyzed enzymes, GSH-per, showed a marked increase after 30 minutes of adenosine treatment, which was potentiated by the hepatotoxin, suggesting an important role of this enzyme in the nucleoside's action; (2) the adenosine catabolism induced an increase in uric acid level, and allopurinol, a purine metabolism inhibitor, prevented such elevation as well as the antilipoperoxidative action of adenosine and the increase of GSH-per associated with the nucleoside treatment. These facts strongly suggest that the protective effect elicited by adenosine is not a direct one, but rather is related to its catabolic products, such as uric acid, which has been recognized as a free radical scavenger.

In vivo correlation between liver and blood energy status as evidenced by chronic treatment of carbon tetrachloride and adenosine to rats

Several tissues, such as red blood cells, depend on the liver supply of the purine ring for adenine nucleotide synthesis. We explored whether progressive liver damage, induced by carbon tetrachloride (CCl4), is accompanied by alterations in liver and blood energy status. After 4 weeks of CCl4 treatment, liver ATP, ATP/ADP, and energy status were decreased. Blood ATP remained normal, whereas the blood energy status was also diminished. After 8 weeks the changes were more evident, and a significant decrease of total liver nucleotides was also found. In the blood, the changes paralleled those in the liver. Simultaneous administration of adenosine counteracted the CCl4 effects. A good correlation (r = 0.79, p < 0.01) between the liver and blood ATP changes and a very significant relationship between liver and blood ATP/ADP ratio (r = 0.92, p < 0.001) were observed. Therefore, the data suggest that liver function could influence the energy availability in other tissues, such as red blood cells, perhaps as a result of its capacity to provide purine rings for extrahepatic synthesis of adenine nucleotides.

Possible role of cell redox state on collagen metabolism in carbon tetrachloride-induced cirrhosis as evidenced by adenosine administration to rats

Marked changes in the redox state of liver cells in carbon tetrachloride (CCl4)-induced cirrhosis after chronic treatment with the hepatotoxin (4-8 weeks) were observed. A shift of the redox state towards the reduced side is noticed in both compartments, cytosol and mitochondria. At 8 weeks of treatment an imbalance between these two compartments was evident. The alteration produced by the CCl4 treatment in the cell redox state might be related to the mitochondrial damage elicited by the hepatotoxin. Adenosine treatment to CCl4-poisoned rats was able to counteract the effect of the hepatotoxin on the redox equilibrium; hence, it could be linked to the beneficial action of the nucleoside in the maintenance of mitochondrial function. The changes in the hepatocyte redox state, induced by CCl4 and/or adenosine, seem to modify collagen and nitrogen metabolism, indicating a linear correlation between the redox state and the collagen synthesis rate, whereas an inverse relationship was observed with collagenase activity. The possible role of the changes in cell redox state as signals for communication between parenchymal and mesenchymal liver cells is discussed. The results suggest an important correlation among mitochondrial function, cellular redox state, and regulation of collagen metabolism that could be relevant for the physio-pathology of this model of experimental cirrhosis.

Effect of omeprazole on gastric first-pass metabolism of ethanol

Some commonly used H2-receptor antagonists affect gastric first-pass metabolism of ethanol and lead to unexpectedly high blood alcohol concentrations after consumption of alcohol. To investigate whether omeprazole--a substituted benzimidazole recently approved for clinical use--has a similar harmful effect, we administered a moderate dose of ethanol (0.3 g/kg body wt) orally to seven normal volunteers before and after one week of omeprazole administration (20 mg daily). No significant effect of the drug was found on either mean peak blood alcohol concentrations or on areas under the blood alcohol curve; neither did these parameters differ significantly before or after an acute dose of omeprazole (13.2 mg/kg body wt) in rats, whether ethanol (0.25 g/kg body wt) was administered intragastrically or intravenously. In vitro, omeprazole in concentrations likely to occur in the gastric lumen (0.01-1.0 mM), did not affect gastric alcohol dehydrogenase activity of humans or rats. Thus omeprazole does not affect gastric first-pass metabolism of ethanol and can be considered as a safe choice for the treatment of patients who do not refrain from alcohol consumption during therapy.

Effects of adenosine administration on the function and membrane composition of liver mitochondria in carbon tetrachloride-induced cirrhosis

The effect of chronic carbon tetrachloride (CCl4) administration on liver mitochondria function and the protective action of adenosine on CCl4-induced damage were assessed in rats made cirrhotic by long-term exposure to the hepatotoxin (8 weeks). The CCl4 treatment decreased the ADP-stimulated oxygen consumption, respiratory control, and ADP/O values, mainly for substrates oxidation of site I, in isolated mitochondria. This impaired mitochondrial capacity for substrate oxidation and ATP synthesis was accompanied by an important diminution (approximately 30 mV) of membrane electrical potential. Disturbances of the mitochondrial membrane, induced by CCl4 treatment, were also evidenced as increased mitochondria swelling and altered oscillatory states of mitochondrial volume, both energy-linked processes. The deleterious effects of CCl4 on mitochondrial function were also reflected as a deficient activity of the malate-aspartate shuttle that correlated with abnormal distribution of cholesterol and phospholipids in membranes obtained from submitochondrial particles. Adenosine treatment of CCl4-poisoned rats partially prevented the alterations in mitochondria membrane composition and prevented, almost completely, the impairment of mitochondria function induced by CCl4. Although the nature of the protective action of adenosine on CCl4-induced mitochondria injury remains to be elucidated, such action at this level might play an important role in the partial prevention of liver damage induced by the CCl4.

Effects of H2-receptor antagonists on gastric alcohol dehydrogenase activity

Inhibition of gastric alcohol dehydrogenase (ADH) activity by cimetidine results in elevated blood levels of ethanol after moderate consumption. To search for alternative H2-blockers lacking such an effect, we compared cimetidine, ranitidine, nizatidine, and famotidine. They inhibited rat gastric ADH noncompetitively, with a Ki for ethanol oxidation of 0.68 mM for cimetidine, 0.5 mM for ranitidine, 1 mM for nizatidine, and 4.5 mM for famotidine. These concentrations are higher than therapeutic plasma levels, but intracellular concentrations in the gastric mucosa (assessed with [3H]cimetidine and [14C]famotidine) were at least 10- and 2-fold greater than in the blood, respectively. These results suggests that, given at therapeutic doses in vivo, the degree of inhibition by cimetidine and ranitidine should be significant and comparable, that by nizatidine should be smaller, and that by famotidine should be negligible. These drugs also exerted either mixed or competitive inhibition of rat hepatic ADH, but the effects of cimetidine and famotidine were observed at concentrations unlikely to occur in vivo. Thus, in alcoholics and in social drinkers who require treatment with H2-receptor antagonists, famotidine might be preferable to the other H2 blockers tested.

Alterations of ATP levels and of energy parameters in the blood of alcoholic and nonalcoholic patients with liver damage

Blood adenine nucleotides were determined in patients with alcoholic and non-alcoholic liver diseases. They included patients with alcoholic hepatitis (AH), alcoholic liver cirrhosis (ALC), non-alcoholic liver cirrhosis (NALC), and amoebic liver abscess (ALA) (28 patients). A decrease of 28% to 39% in blood ATP levels was observed among the patients with AH and the cirrhotic groups, respectively (p less than 0.05), whereas no significant changes in blood ATP levels were detected in the ALA group. Although total blood adenine nucleotides were significantly diminished in AH, ALC, and NALC groups, the AH patients retained their energy relationships within normal range. On the other hand, the cirrhotic groups, independently of their etiology, failed to maintain an adequate ATP/ADP ratio, energy charge, and phosphorylation potential in the blood, suggesting a decreased energy availability in their blood cells. Nevertheless, the mechanism involved in these effects remains to be elucidated, a failure of the damaged liver to supply purines to extra-hepatic tissues might be a major event altering the blood energy parameters.

Twenty-four-hour changes of S-adenosylmethionine, S-adenosylhomocysteine adenosine and their metabolizing enzymes in rat liver; possible physiological significance in phospholipid methylation

1. The metabolic control of adenosine concentration in the rat liver through the 24-hr cycle is related to the activity of adenosine-metabolizing enzymes [5'-nucleotidase (5'N), adenosine deaminase (A.D.), adenosine kinase (A.K.) and S-adenosylhomocysteine hydrolase (SAH-H)]. 2. Two peaks of adenosine were observed, one at 12:00 hr caused by high activity of 5'N and SAH-H, and the other at 02:00 hr, caused by a decrease in purine catabolism and purine utilization, low activity of SAH-H and de novo purine formation. 3. The similarity of the adenosine and S-adenosylmethionine (SAM) profiles through the 24-hr cycle suggests a role of adenosine in transmethylation reactions, because, during the night (02:00 hr), the metabolic conditions favor the formation and accumulation of S-adenosylhomocysteine (SAH), with consequent inhibition of transmethylation reactions. 4. In the 24-hr variation of phosphatidylcholine (PC) and phosphatidylethanolamine (PE), the lowest ratio of PC/PE was observed at 24:00-02:00 hr when SAH concentration is high, whereas the highest PC/PE ratio occurs at the same time as one of the SAM/SAH ratio maxima.

Lack of alcohol dehydrogenase isoenzyme activities in the stomach of Japanese subjects

Alcohol dehydrogenase (ADH) isoenzymes different from those of the liver were shown to be present in the human gastric mucosa. Two ADH activity bands present in the gastric mucosa of surgical specimens from all 7 black and 11 white Americans studied were absent in 14 and barely detectable in 3 of 21 Japanese subjects evaluated. Similar ethnic differences pertained to both genders and were independent of the gastric pathology. The mobility of these bands on starch gel electrophoresis corresponded to those recently reported and named mu-ADH or sigma-ADH. The absence of these bands was associated with a 70% decreased capacity to reduce m-nitrobenzaldehyde, a preferred substrate for sigma-ADH, suggesting that the bands missing from the Japanese stomachs comprise this isoenzyme.

Human gastric alcohol dehydrogenase: its inhibition by H2-receptor antagonists, and its effect on the bioavailability of ethanol

Two types of alcohol dehydrogenase isoenzymes (differing in their affinity for ethanol, sensitivity to 4-methylpyrazole, and electrophoretic migration) have been identified in the human stomach. At the high ethanol concentrations prevailing in the gastric lumen during alcohol consumption, the sum of their activities could account for significant oxidation of ethanol. In vitro, these activities were inhibited by cimetidine and ranitidine, but not by famotidine. In vivo, therapeutic doses of cimetidine (but not of famotidine) increased blood ethanol levels when ethanol was given orally, but not when it was given intravenously, indicating a significant contribution of the gastric ADH to the bioavailability and thereby the potential toxicity of ethanol.

Adenosine partially prevents cirrhosis induced by carbon tetrachloride in rats

Adenosine administration was tested in rats with carbon tetrachloride-induced hepatic fibrosis and was able to partially prevent the enlargement of liver and spleen induced by the toxin. This amelioration of the hepatomegaly was accompanied by a 50% reduction of the liver collagen deposition and preservation of content of glycosaminoglycans. A stimulated hepatic collagenase activity is apparently the mechanism for reduction of collagen accumulation. These effects were associated with a striking improvement in liver function. Adenosine treatment did not modify the late hepatotoxic effect of the carbon tetrachloride; however, the stimulatory effect of the nucleoside on energy state appeared to counteract the drastic decreases in adenine nucleotides, ATP, ATP/ADP ratio and energy charge elicited by the hepatotoxin. Moreover, a possible beneficial action of enhanced hepatic oxygenation caused by the vasodilator properties of adenosine cannot be ruled out. Regardless of the mechanism, adenosine seems to change the cellular response to the injury induced by the hepatotoxin.

High levels of acetaldehyde in nonalcoholic liver injury after threonine or ethanol administration

Acetaldehyde, a product of ethanol oxidation which forms adducts with proteins, has been incriminated in the pathogenesis of alcoholic liver injury. High serum antibody titers against acetaldehyde-protein adducts have been found not only in alcoholics but also in patients with nonalcoholic liver disease, suggesting a contribution of acetaldehyde derived from sources other than exogenous ethanol. To investigate the effect of liver injury on the removal and the production of acetaldehyde, we produced fibrosis and cirrhosis (by chronic administration of carbon tetrachloride) and fatty liver (with very small doses of dimethylnitrosamine) in rats. Endogenous blood acetaldehyde levels increased by 38% in rats with severe liver injury (p less than 0.005), but not significantly in rats with fatty liver. However, an i.v. load of threonine (a physiological source of acetaldehyde), in amounts equivalent to the daily intake of this amino acid, increased blood and hepatic acetaldehyde levels in the rats with both types of liver injury more than in controls. Threonine dehydrogenase and dehydratase activities, involved in the major pathways for threonine degradation in mitochondria and cytosol, respectively, were markedly decreased in rats with liver injury with a resulting increase in hepatic threonine concentration. Moreover, the threonine aldolase activity, which splits threonine into glycine and acetaldehyde, remained unaffected or even slightly increased. Liver injury was also associated with impaired mitochondrial functions, including a 10 to 23% decrease in acetaldehyde oxidation (depending upon the severity of the lesions). As a consequence, administration of ethanol (an exogenous source of acetaldehyde) resulted in striking elevations in the levels of acetaldehyde in carbon tetrachloride-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Gastric origin of the first-pass metabolism of ethanol in humans: effect of gastrectomy

The areas under the curve (AUCs) of blood ethanol concentrations are much smaller after oral than after intravenous administration of a small dose of ethanol. To study whether this difference is due to ethanol oxidation in the stomach, in the small intestine, or during first pass through the liver, we compared the AUCs after random administration of the same ethanol dose by the intravenous, oral, and intraduodenal routes to 5 abstaining alcoholics and via the two former routes to 10 subjects with Billroth II subtotal gastrectomy. In the nonoperated subjects, the AUCs after an ethanol dose (0.15 g/kg) given orally were 17% (p less than 0.01) of those achieved intravenously, in spite of the fact that greater than 99% of the dose had disappeared from the stomach at the completion of the AUC. By contrast, the AUCs after intraduodenal administration did not differ from those produced intravenously, indicating that neither the intestine nor the liver make a detectable contribution to this first-pass metabolism. Moreover, gastrectomy completely abolished the first-pass metabolism of ethanol. Gastric metabolism decreases the bioavailability of the ingested alcohol and thus attenuates its systemic toxicity. The abolition of this "protective barrier" in gastrectomized patients may increase their vulnerability to ethanol.

Characterization of the increased binding of acetaldehyde to red blood cells in alcoholics

Using equilibrium dialysis, we found that acetaldehyde, at the levels commonly occurring after ethanol ingestion, did not bind detectably to plasma proteins, but there was significant binding to red blood cells, more in alcoholics than in nonalcoholics. The binding to red blood cells was inhibited by pyridoxal phosphate and N-ethylmaleimide, suggesting adduction to amino and thiol groups. Binding kinetics were consistent with at least two sites. The one with the highest affinity for acetaldehyde corresponded to hemoglobin. Its affinity and Bmax were not changed in alcoholics, but these binding sites accounted for only 44% of the sites available in the red blood cells of alcoholics and 80% of those in controls. Moreover, this binding was not inhibited by N-ethylmaleimide. There was no detectable binding to red cell ghosts. Nonprotein binding was then assessed by changes in NADH produced by the addition of protein-free fractions of the cells to an alcohol dehydrogenase system in equilibrium; this revealed a second binder of lower affinity, larger capacity and with sensitivity to both inhibitors. This binding (possibly due to thiazolidine formation with cysteine) was enhanced in alcoholics, whose red blood cell cysteine content was doubled. Levels of red blood cell cysteine and acetaldehyde remained high for 2 weeks after withdrawal. Because of the prolonged persistence after withdrawal, these changes may provide new markers of alcoholism.

Impaired oxygen utilization. A new mechanism for the hepatotoxicity of ethanol in sub-human primates

The role of oxygenation in the pathogenesis of alcoholic liver injury was investigated in six baboons fed alcohol chronically and in six pair-fed controls. All animals fed alcohol developed fatty liver with, in addition, fibrosis in three. No evidence for hypoxia was found, both in the basal state and after ethanol at moderate (30 mM) or high (55 mM) levels, as shown by unchanged or even increased hepatic venous partial pressure of O2 and O2 saturation of hemoglobin in the tissue. In controls, ethanol administration resulted in enhanced O2 consumption (offset by a commitant increase in splanchnic blood flow), whereas in alcohol fed animals, there was no increase. At the moderate ethanol dose, the flow-independent O2 extraction, measured by reflectance spectroscopy on the liver surface, tended to increase in control animals only, whereas a significant decrease was observed after the high ethanol dose in the alcohol-treated baboons. This was associated with a marked shift in the mitochondrial redox level in the alcohol-fed (but not in control) baboons, with striking rises in splanchnic output of glutamic dehydrogenase and acetaldehyde, reflecting mitochondrial injury. Increased acetaldehyde, in turn, may aggravate the mitochondrial damage and exacerbate defective O2 utilization. Thus impaired O2 consumption rather than lack of O2 supply characterizes liver injury produced by high ethanol levels in baboons fed alcohol chronically.

In vivo and in vitro adenosine stimulation of ethanol oxidation by hepatocytes, and the role of the malate-aspartate shuttle

In this study, a pronounced increase of ethanol oxidation was found in hepatocytes obtained from adenosine-treated rats, or after in vitro additional of the nucleoside; this finding was accompanied by a maintenance of the normal cytoplasmic redox state. These results suggest a higher availability of cytoplasmic NAD in these cells. Therefore, the metabolic pathways which carry out the reoxidation of cytosolic reducing equivalents, namely, malate-aspartate and alpha-glycerophosphate shuttles, were examined. Isolated mitochondria from adenosine-treated rats had an increased NADH oxidation by the malate-aspartate shuttle; furthermore, in vivo and in vitro addition of adenosine to the hepatocytes induced changes in the equilibrium of the malate-aspartate shuttle, as evidenced by the subcellular distribution of the intermediates of this pathway. Acetaldehyde removal was also increased by adenosine and this fact was related to an elevated NAD/NADH ratio in the mitochondria. Thus, under these conditions, an increased ethanol uptake was accompanied by enhanced acetaldehyde removal in the animal. In conclusion, adenosine administration stimulates the transport of cytoplasmic reducing equivalents to the mitochondria, mainly through the malate-aspartate shuttle. This action, which may be located at the level of the mitochondrial membrane, is reflected by an enhancement of ethanol and acetaldehyde oxidations.

Day-night cycle of lipidic composition in rat cerebral cortex

A study of the lipidic pattern of the cerebral cortex of the normal adult rat during the day-night cycle was carried out. The changes observed were the following: phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol and phosphatidylserine plus phosphatidic acid showed a peak at 16:00 hr possibly due to a general increase in phospholipid biosynthesis. During the nocturnal period the variations of phosphatidylcholine and phosphatidylethanolamine were not clearly observed, they might be due to an increase in the interconversion or exchange reaction, since the ratio phosphatidylcholine/phosphatidylethanolamine showed a significative change at 04:00 hr. This occurred because small but opposite changes in both phospholipids were observed, suggesting an increase in the methylation reactions of phospholipids. Cardiolipin showed a significant peak at 04:00 hr. Plasmalogens exhibited significative changes, an important diminution at 16:00 hr and a prominent peak at 24:00 hr. Cholesterol levels were high during the light period and low in the dark one. Cerebrosides and gangliosides showed no day-night variations. The changes observed indicate a phenomenon of biological rhythmicity synchronized by the photoperiod, suggesting that these fluctuations could act as physiological modulators of the properties and functions of the nerve cell membrane.

Day-night cycle of lipid peroxidation in rat cerebral cortex and their relationship to the glutathione cycle and superoxide dismutase activity

Lipoperoxidation, glutathione cycle components and superoxide dismutase activity show a day-night rhythm in the cerebral cortex of the rat. The highest lipoperoxidative activity is observed during the night (20.00-04.00 h). The enhancement in lipoperoxidation occurs concurrently with a decrease in glutathione peroxidase activity, an increase in superoxide dismutase activity and an increase in the double bonds in the brain cortex lipid fraction. The changes described in this paper seem to be related to a succession of light and dark periods, or to fasting and feeding periods. We propose that those fluctuations could act as a physiological oscillator with an important role in modulating the membrane properties of the nerve cell.

Effects of adenosine on liver cell damage induced by carbon tetrachloride

Adenosine administration delayed the fatty liver and cell necrosis induced by carbon tetrachloride without affecting the action of the hepatotoxin on protein synthesis and liver triacylglycerol release. Adenosine produced a drastic antilipolytic effect accompanied by a decrease in the incorporation of [1-14C]palmitic acid into triacylglycerols and free fatty acids of the liver. Furthermore, a decrease in the serum levels of ketone bodies was observed at early times. The nucleoside also avoided the release of intracellular enzymes and prevented the lipid peroxidation produced by carbon tetrachloride during the 4 hr of treatment. The protective action of adenosine was transient, lasting 3-4 hr, probably the time required to be metabolized. The results suggest that the antilipolytic effect of the nucleoside, the inhibition of hepatic fatty acid metabolism, and the decrease in carbon tetrachloride-induced lipoperoxidation that it produced are involved in the delayed acute hepatotoxicity induced by carbon tetrachloride.

Circadian variations of adenosine level in blood and liver and its possible physiological significance

The role of adenosine as a possible physiological modulator was explored by measuring its concentration in different tissues during a 24-hour period. Initially the circadian variations of adenosine and other purine compounds such as inosine, hypoxanthine, uric acid and adenine nucleotides were studied in the rat blood. A daily cyclic response was observed, with low levels of adenosine from 08.00 - 20.00 h, followed by an increase from this time on. Inosine and hypoxanthine levels were elevated during the day and low at night. The uric acid changes observed indicate that the decrease in purine catabolism coincides with a decrease in inosine and hypoxanthine levels and an increase in adenosine. The blood adenine nucleotides, energy charge and phosphorylation potential remained constant during the day and showed oscillatory changes during the night. Similar studies were made in the liver, a primary source of circulating purines. Liver adenosine was high during the night while inosine and hypoxanthine remained low along the 24 hours. The results suggest that liver purine metabolism might participate in the maintenance and renewal of the blood purine pool and in the energy state of erythrocytes in vivo.