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.

Inhibition of S-adenosyl-L-homocysteine hydrolase by adrenaline in isolated guinea-pig papillary muscles

Purified S-adenosyl-L-homocysteine hydrolase from Dictyostelium discoideum or rabbit erythrocytes is inactivated when incubated with cAMP. The aim of this study was to investigate whether adrenaline, which increases cytosolic cAMP and calcium concentrations, is able to modify in situ the activity of S-adenosyl-L-homocysteine hydrolase in the heart. The enzyme was assayed in a crude extract obtained from superfused guinea-pig papillary muscles with the different tested substances. Adrenaline was found to inhibit S-adenosyl-L-homocysteine hydrolase in papillary muscles in a concentration-dependent fashion. This inhibition was associated with an increase in the concentration of S-adenosyl-L-homocysteine (326%), and a decrease of adenosine (40%). beta-Adrenoceptors are involved in the effect of adrenaline, since isoproterenol, a beta-adrenergic agonist, inhibited the enzyme, whereas the beta-adrenergic blocker, propranolol, prevented this inhibition. Participation of calcium in the inhibitory effect of adrenaline was suggested because the calcium channel blocker, verapamil, suppressed this inhibition, and high calcium in the perfusion medium inhibited the enzyme. In vitro experiments with calcium were performed in a semi-purified fraction of the enzyme, resulting in a concentration-dependent inhibition of the enzyme. Calcium concentration, which inhibited the enzyme 50%, was in the millimolar range for control and in the micromolar range for the obtained enzyme from adrenaline-treated muscles, indicating a different sensitivity to calcium inhibition. We conclude that adrenaline inhibits S-adenosyl-L-homocysteine hydrolase in situ, probably by a calcium-modulated mechanism.

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.

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.

Topoisomerase activity during the heat shock response in Escherichia coli K-12

During the upshift of temperature from 30 to 42, 45, 47, or 50 degrees C, an increase in the level of supercoiling of a reporter plasmid was observed. This increase was present in groE and dnaK mutants but was inhibited in cells treated with chloramphenicol and novobiocin. The intracellular [ATP]/[ADP] ratio increased rapidly after an upshift in temperature from 30 to 47 degrees C and then decreased to reach a level above that observed at 30 degrees C. These results suggest that gyrase and proteins synthesized during heat shock are responsible for the changes seen in plasmid supercoiling. Proteins GroE and DnaK are probably not involved in this phenomenon.

Circadian variations of adenosine and of its metabolism. Could adenosine be a molecular oscillator for circadian rhythms?

The present review describes the biological implications of the periodic changes of adenosine concentrations in different tissues of the rat. Adenosine is a purine molecule that could have been formed in the prebiotic chemical evolution and has been preserved. The rhythmicity of this molecule, as well as its metabolism and even the presence of specific receptors, suggests a regulatory role in eukaryotic cells and in multicellular organisms. Adenosine may be considered a chemical messenger and its action could take place at the level of the same cell (autocrine), the same tissue (paracrine), or on separate organs (endocrine). Exploration of the circadian variations of adenosine was planned considering the liver as an important tissue for purine formation, the blood as a vehicle among tissues, and the brain as the possible acceptor for hepatic adenosine or its metabolites. The rats used in these studies were adapted to a dark-light cycle of 12 h with an unrestrained feeding and drinking schedule. The metabolic control of adenosine concentration in the different tissues studied through the 24-h cycle is related to the activity of adenosine-metabolizing enzyme: 5'-nucleotidase adenosine deaminase, adenosine kinase, and S-adenosylhomocysteine hydrolase. Some possibilities of the factors modulating the activity of these enzymes are commented upon. The multiphysiological action of adenosine could be mediated by several actions: (i) by interaction with extracellular and intracellular receptors and (ii) through its metabolism modulating the methylation pathway, possibly inducing physiological lipoperoxidation, or participating in the energetic homeostasis of the cell. The physiological meaning of the circadian variations of adenosine and its metabolism was focused on: maintenance of the energetic homeostasis of the tissues, modulation of membrane structure and function, regulation of fasting and feeding metabolic pattern, and its participation in the sleep-wake cycle. From these considerations, we suggest that adenosine could be a molecular oscillator involved in the circadian pattern of biological activity in the rat.

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.

Day-night variations of adenosine and its metabolizing enzymes in the brain cortex of the rat--possible physiological significance for the energetic homeostasis and the sleep-wake cycle

The role of adenosine as a metabolic regulator of physiological processes in the brain was studied by measuring its concentrations and the activity of adenosine-metabolizing enzymes: 5'-nucleotidase, S-adenosylhomocysteine hydrolase, adenosine deaminase and adenosine kinase in the cerebral cortex of the rat. Other purine compounds, such as, inosine, hypoxanthine and adenine nucleotides were also studied. The purines' pattern was bimodal with high levels of adenosine, inosine and hypoxanthine during the light period reaching their peak at 12.00 h, 08.00 h and 16.00 h, respectively, and small increments during the night between 02.00 h and 04.00 h. The enzymatic activities showed, in general, an unimodal profile with low activity during the day and high activities at night. The adenine nucleotide profile showed a significant diminution between 12.00 h and 24.00 h. The high adenosine level during the day might be due to a diminution of adenine nucleotide and to the low activity of adenosine-metabolizing enzymes, suggesting an accumulation of the nucleoside. The night increase, although of less magnitude, is simultaneous to high activity of adenosine-metabolizing enzymes and could be due to an increased formation of the nucleoside. The present data and the findings from other authors strongly suggest that adenosine in the brain cortex of the rat can participate at least in two physiological processes: regulation of the sleep-wake cycle and replenishment of the adenine nucleotide pool.

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.

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.

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.

Effect of age and day time on the adenosine modulation of basal and insulin-stimulated glucose transport in rat adipocytes

1. The relationship between the activity of adenosine metabolizing enzymes 5'nucleotidase (5'N), adenosine kinase (A.K.) and adenosine deaminase (A.D.) with basal and insulin-stimulated glucose transport in isolated fat cells from young and old animals was studied at 08:00 and 16:00 hr. 2. In cells from young animals a larger insulin-stimulation of glucose transport was observed at 16:00 hr than at 08:00 hr. Also at 16:00 hr small changes in 5'N, A.K. and A.D. activities suggest a decrease in adenosine formation. 3. In the cells from old animals no effect of insulin was observed at any time, while a 3-5-fold increase in 5'N indicated a predominance of adenosine formation at both times studied. 4. An inverse relationship was observed in the changes of adenosine metabolism and insulin action.

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.

Effect of adenosine on the serum levels of glucose, insulin and glucagon in vivo

The in vivo effect of adenosine on the serum levels of glucose, insulin and glucagon in rats fasted for twenty four hours or after an oral glucose load were studied. Under fasting conditions adenosine produced an hyperglycaemia without change in the insulin or glucagon serum levels. After a glucose load adenosine induced a marked hyperglycaemia concomitant to a decrease in insulin serum levels and an increase in glucagon serum levels. Adenosine did not alter the relationship between insulin and glucagon. In vivo adenosine administration altered the secretion of hormones by the islets of Langerhans (increased the release of glucagon and decreased the secretion of insulin) but this was only clearly observable under stimulated conditions. Adenosine did not alter the regulatory mechanism(s) that modulate the relationship between insulin and glucagon.

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.

Stimulatory action of cycloheximide on glucose metabolism in the rat epididymal fat pad

The action of cycloheximide on some parameters of glucose and lipid metabolism was studied in vitro in epidiymal fat pads from fasted rats. Incubation of fat pads with cycloheximide (1 mug/ml) for 2 hours resulted in a two-fold increase in glucose uptake, glucose oxidation, incorporation of glucose into lipids, and reesterification of free fatty acid. The increase in glucose oxidation was evident in experiments in which [U-14C], [1-14C], or [6-14C]glucose was added to the media, but it was absent when the media were supplemented with pyruvate. Incorporation of glucose into glycogen and accumulation of lactate in the medium were not seriously modified by the presence of cycloheximide. The stimulatory effect of cycloheximide on incorporation of glucose into lipids was absent when insulin or cortisol was added to the medium. A cycloheximide-mediated increase in glucose uptake seems to be responsible for the subsequent changes in glucose metabolism, and would seem to be independent of an inhibition in protein synthesis; puromycin and actinomycin D did not mimic the cycloheximide action on glucose incorporation into lipids.