In vitro and in vivo effects of methyl isocyanate on rat brain mitochondrial respiration

The present study deals with the in vitro and in vivo effects of methyl isocyanate (MIC) on rat brain mitochondrial function. Addition of MIC to tightly coupled brain mitochondria in vitro resulted in a mild stimulation of state 4 respiration, abolition of respiratory control, decrease in ADP/O ratio, and inhibition of state 3 oxidation. The oxidation of NAD⁺-linked substrates (glutamate + malate) was more sensitive (fourfold) to the inhibitory action of MIC than succinate while cytochrome oxidase was unaffected. Administration of MIC subcutaneously at a lethal dose affected respiration only with glutamate + malate as the substrate (site I) and caused a 20% decrease in state 3 oxidation leading to a significant decrease in respiratory control index while state 4 respiration and ADP/O ratio remained unaffected. As both the malondialdehyde and iron contents of brain mitochondria were not altered, it may be inferred that the observed in vivo inhibition of state 3 oxidation is induced by MIC through systemic stagnant hypoxia leading to ischemia of brain, which further contributes to the cerebral hypoxia.     

Effect of hypoenergetic feeding on muscle oxidative phosphorylation and mitochondrial complex I-IV activities in rats

BACKGROUND: Previous studies showed that malnutrition reduces the activity of complexes I, II, and III in the mitochondria of skeletal muscle. OBJECTIVE: We hypothesized that malnutrition would influence oxidative phosphorylation and mitochondrial complex activity in the skeletal muscle of rats. DESIGN: Thirty-two rats were assigned either to a control group with an ad libitum intake of 364 kJ/d or to a hypoenergetic group with an intake of 92 kJ/d. Eleven of these rats received the hypoenergetic diet for 10 d, 2 for 5 d, 2 for 6 d, 2 for 7 d, and 1 each for 8 and 11 d to achieve a distributed weight loss. Ten controls were fed for 10 d, 2 for 7 d, and 1 for 5 d, to match day 10, day 5, and the midpoint (day 7) of 6-8 d of hypoenergetic feeding. The 2 diets provided the same volume, electrolytes, vitamins, and trace elements but different amounts of energy. RESULTS: A significant relation was observed between weight loss and the state 4 and 3 oxidation rates with pyruvate + malate and for state 3 glutamate + malate and succinate + rotenone but not with tetramethyl-p-phenylenediamine + ascorbate + antimycin A (TMPD). Similarly, a significant relation was observed between the degree of weight loss and complex I and III activities but not with complex II and IV activities. CONCLUSIONS: The complex activities of the mitochondrial oxidative phosphorylation chain in muscle were depressed selectively with energy deprivation when compared with normally fed rats. These findings may partly explain the mechanism of reduced muscle energetics in energy malnutrition.     

Effect of heptachlor on hepatic mitochondrial oxidative phosphorylation in rat

In a study of the hepatotoxicity of heptachlor (1,4,5,6,7,8,8-heptachlor 3a, 4,7,7 a-tetrahydro-4,7-methanoindene), a major compound of chlordane, the effect of heptachlor on the respiratory activity (oxidative phosphorylation and electron transport) of rat liver mitochondria was investigated. Heptachlor at a final concentration of 50 microM with succinate as substrate decreased the respiratory control index (RCI) due to a marked inhibition of state 3 respiration and a slight inhibition of state 4 respiration. One hundred microM heptachlor with succinate as substrate suppressed the states 3 and 4 respiration almost completely. On the other hand, heptachlor at a final concentration ranging from 50 to 100 microM with beta-hydroxybutylate (beta-HB) slightly decreased the RCI and decreased the RCI hardly at all with ascorbate plus N,N,N',N', -tetramethylphenylene diamine (TMPD) as substrate. Heptachlor at a concentration of 50 microM in the presence of succinate also decreased the ADP/O ratio of mitochondria. The mode of inhibition of succinate oxidation by heptachlor apparently is a noncompetitive inhibition, as shown by Lineweaver-Burk plot.     

Comparative study of the effects of biphenyl and Kanechlor-400 on the respiratory and energy linked activities of rat liver mitochondria

A comparative study of the effects of biphenyl and Kanechlor-400 (KC-400) on the respiratory and energy linked activities of rat liver mitochondria was made, and some differences in effects caused by the chlorination of biphenyl were clarified. The inhibition of state 3 respiration with succinate by biphenyl was less than that observed with alpha-ketoglutarate/malate. By contrast, KC-400 exhibited the opposite trend; state 3 respiration with succinate was more sensitive to inhibition than that observed with alpha-ketoglutarate/malate. Thus the inhibition of state 3 respiration with NAD+-linked substrate was decreased, whereas the inhibition of state 3 respiration with succinate was increased by the chlorination of aromatic rings. Biphenyl also instantaneously stimulated state 4 respiration. The extent of stimulation with succinate by biphenyl was larger than with alpha-ketoglutarate-malate. On the other hand, there was about a 1-2 minute lag period before stimulation of state 4 respiration by KC-400 became obvious. Furthermore, state 4 respiration in the presence of alpha-ketoglutarate/malate was more intensely stimulated by KC-400 than by succinate. Biphenyl and KC-400 dissipated the membrane potential across the mitochondrial membranes. The dissipation of membrane potential by biphenyl was instantaneous whereas that caused by KC-400 was preceded by a lag period (1-2 min). Biphenyl and KC-400 altered the permeability properties of mitochondrial membranes as evidenced by the release of endogenous K+. The release of K+ due to biphenyl was instantaneous but KC-400 induced K+-release was preceded by a lag period (1-2 min). Thus membrane perturbation by biphenyl was faster than that induced by KC-400. Therefore, it is clear that the chlorination of aromatic rings delays the perturbation in the state of membrane lipids.     

Comparative study of the effects of biphenyl and Kanechlor-400 on the respiratory and energy linked activities of rat liver mitochondria.

A comparative study of the effects of biphenyl and Kanechlor-400 (KC-400) on the respiratory and energy linked activities of rat liver mitochondria was made, and some differences in effects caused by the chlorination of biphenyl were clarified. The inhibition of state 3 respiration with succinate by biphenyl was less than that observed with alpha-ketoglutarate/malate. By contrast, KC-400 exhibited the opposite trend; state 3 respiration with succinate was more sensitive to inhibition than that observed with alpha-ketoglutarate/malate. Thus the inhibition of state 3 respiration with NAD+-linked substrate was decreased, whereas the inhibition of state 3 respiration with succinate was increased by the chlorination of aromatic rings. Biphenyl also instantaneously stimulated state 4 respiration. The extent of stimulation with succinate by biphenyl was larger than with alpha-ketoglutarate-malate. On the other hand, there was about a 1-2 minute lag period before stimulation of state 4 respiration by KC-400 became obvious. Furthermore, state 4 respiration in the presence of alpha-ketoglutarate/malate was more intensely stimulated by KC-400 than by succinate. Biphenyl and KC-400 dissipated the membrane potential across the mitochondrial membranes. The dissipation of membrane potential by biphenyl was instantaneous whereas that caused by KC-400 was preceded by a lag period (1-2 min). Biphenyl and KC-400 altered the permeability properties of mitochondrial membranes as evidenced by the release of endogenous K+. The release of K+ due to biphenyl was instantaneous but KC-400 induced K+-release was preceded by a lag period (1-2 min). Thus membrane perturbation by biphenyl was faster than that induced by KC-400. Therefore, it is clear that the chlorination of aromatic rings delays the perturbation in the state of membrane lipids.     

Effects of polychlorinated biphenyls (Kanechlor-400) on isolated rat liver mitochondria

The effects of the polychlorinated biphenyls (Kanechlor-300, 400, 500, and 600) on the functions of isolated rat liver mitochondria were studied. Kanechlor-400 (KC-400) inhibited state 3 respiration with either succinate or α-ketoglutarate/malate, but not with ascorbate/N,N,N,N-tetrame-thylphenylenediamine (TMPD) as a substrate. The inhibition of state 3 respiration in the presence of succinate was greater than that observed with α-keto-glutarate/malate. The enzymatic analysis showed that KC-400 inhibited succinate dehydrogenase and the CoQ-cytochrome c region of the electron transport chain. Therefore, the inhibition of state 3 respiration due to KC-400 was caused by the blockage of the electron transport chain. KC-400 also uncouples oxidative phosphorylation as evidenced by stimulation of state 4 respiration and latent ATPase activity, although the uncoupling action was masked at higher concentrations by progressive inhibition of the electron transport chain. The inhibitory actions of KC-300, 400, and 500 on state 3 respiration in the presence of succinate were almost equal, whereas the inhibitory action of KC-600 was weaker than the other KCs. The order of stimulatory abilities of KCs on state 4 respiration in the presence of succinate was KC-300 > KC-400 > KC-500; KC-600 had no stimulatory effect. Excessive chlorination of the aromatic rings may weaken the interaction of PCBs with membrane proteins or lipids of mitochondria.     

Effects of moderate chronic ethanol consumption on rat liver mitochondrial functions

The biochemical consequences of moderate chronic ethanol ingestion has been scarcely investigated in spite of the fact that most of the human population drinks ethanol on a moderate basis. This paper describes some metabolic effects produced by moderate ethanol consumption. The substitution of drinking water in rats for a 10% ethanol solution during 4 weeks resulted in: a) a decrease of blood urea and citrulline synthesis in liver mitochondria; b) a slight inhibition in state 3 and state 4 respiration either with glutamate-malate as substrates or succinate as substrate; c) no change in ADP/O ratio with succinate but slight increase with glutamate-malate; d) a reduction of the cytochrome oxidase activity and cytochromes a+a3 content; e) a 42% increase in the succinate dehydrogenase activity and a small but constant increase in the Vmax (no change in the Km) of the adenine nucleotide translocase activity in liver mitochondria. These results show that even moderate, but continuous ethanol ingestion, produces metabolic responses that must be carefully evaluated to define health risk in larger human groups.     

Inhibitory effects of vanadium pentoxide on respiration of rat liver mitochondria

The bioenergetic functions of liver mitochondria were studied following the acute and chronic exposure of rats to vanadium pentoxidevia respiratory tract. The mitochondrial respiration with glutamate or succinate as substrate was inhibited significantly when compared to the control animals. No inhibition was found with ascorbate. The same effects were observedin vitro. Vanadium (V) was responsible for these inhibitory effects. It is postulated that significant amounts of vanadate are accumulated in the intermembrane space of liver mitochondria of the exposed rats. The process of detoxification by reduction of vanadate in the tissue may be insufficient to prevent the deleterious action of this compound on liver mitochondria.     

Gender-related differences in mouse hepatic ethanol metabolism

The effect of an acute oral load of 2 g ethanol/kg body weight was studied in a group of male and female 10-wk-old C3H/HeNCrj (C3H/He) mice to investigate gender change throughout differences of the hepatic ethanol metabolism of mice. The following parameters were measured in the serum from 0 h to 3 h after the start of the experiment: ethanol, acetaldehyde, and acetate. Their concentrations in the serum in female mice tended to show lower levels than in male mice. In female mice, the concentration of ethanol at 1 h and the concentration of acetate at 1 h, 2 h, and 3 h after ethanol administration showed significantly lower levels than in male mice. Ten-week-old male and female C3H/He mice were subcutaneously injected 50 microg/kg body weight beta-estradiol and 1.45 mmol/kg body weight testosterone propionate (testosterone) in olive oil, respectively, and changes in the activity of enzymes related to the hepatic ethanol metabolism of mice were examined at 24 h after the administration of sex hormones. The activity of the cytosolic alcohol dehydrogenase (ADH) and microsomal aniline hydroxylase (ANH) and the low Km, high Km and total aldehyde dehydrogenase (AlDH) activities in the mitochondrial, the cytosolic, and the microsomal fraction of the liver were higher. Moreover, the density of the band of CYP2E1 in the microsome in female mice was stronger than in male mice, and in the microsomal fraction of the liver, the total content of cytochrome P-450 (CYP) and ethoxyresorufin O-dealkylase (EROD) activity in male mice showed significantly higher values than in female mice. The density of the band of CYP2E1 and the three activities of AlDH in the hepatic mitochondrial fraction of male mice increased significantly under treatment with beta-estradiol. The three activities of AlDH of the cytosolic fraction of the liver in female mice significantly decreased under treatment with testosterone. The present findings suggested that in C3H/He mice livers, the rate of ethanol metabolism is faster in females than in males, and the enzymes related to ethanol metabolism are controlled by testosterone or beta-estradiol. It is suggested that ethanol and its metabolite disappear faster from the serum of female mice than from the serum of male mice because the activities of hepatic enzymes related to ethanol metabolism are higher in female mice than in male mice. C3H/He mice, hepatic ethanol metabolism, gender different, ADH, AlDH     

ALTERATION OF ACETALDEHYDE METABOLISM IN CARBON TETRACHLORIDE-INTOXICATED RAT LIVER: ANALYSIS USING LIVER PERFUSION SYSTEM

The hepatic metabolism of acetaldehyde in carbon tetrachloride(CCl₄)-intoxicated rats was studied using a non-recirculatinghaemoglobin-free liver-perfusion system. Acetaldehyde uptakeby the liver from acutely CCl₄-treated animals (4.16 mmol/kg,i.p.) at 24 hr after the treatment was not significantly altered,whereas that by the liver from chronically CCl₄-treated animals(2.08 mmol/kg,i.p., twice a week, for 8–12 weeks) wasdecreased by approximately 50% when it was determined in thepresence of 0.01–5 mM acetaldehyde. In liver from ratschronically intoxicated with CCl₄, the following important biochemicalchanges were observed: (1) The activity of low K_m aldehyde dehydrogenase(ALDH) in hepatic mitochondria was decreased by approximately75%. (2) The basal levels of the lactate/pyruvate (cytosolic[NADH]/[NAD⁺]) ratio as well as the ß-hydroxybutyrate/acetoacetate(mitochondrial [NADH]/[NAD⁺]) ratio were elevated by more than2-fold. (3) Mitochondrial NADH oxidation was also reduced byapproximately 35% of the control level. (4) The basal levelof hepatic oxygen uptake was attenuated by approximately 50%,and the infusion of acetaldehyde (0.01–5.0 mM) causeda further decrease in the uptake. (5) The rate of ethanol productionfrom acetaldehyde by the catalytic action of alcohol dehydrogenasewas found to be unaltered when low concentrations of acetaldehyde(0.01–0.2 mM) were used, whereas a significant suppressionof the rate of ethanol production was detected in the presenceof high concentrations of acetaldehyde (0.6–5 mM). Thesedata suggest that the changes in activity of the lowK_m mitochondrialacetaldehyde dehydrogenase and those in mitochondrial NADH oxidationcoupled with mitochondrial respiration may, at least in part,play important roles in the decreased hepatic acetaldehyde metabolismobserved in chronically CCl₄-treated rats.     

Use of cyanamide to determine localization of acetaldehyde metabolism in rat liver

Various techniques have been employed previously to show that acetaldehyde is primarily oxidized in the mitochondrial matrix of rat liver. In this study, a new approach was tested. Mitochondrial low-Km aldehyde dehydrogenase (ALDH) was partially inactivated and the effect on acetaldehyde oxidation measured. Cyanamide was chosen as the ALDH inhibitor. An enzymatic activation of cyanamide, probably by catalase, was necessary for the drug to inhibit ALDH activity. The level of remaining ALDH activity after cyanamide treatment was correlated with the ability of either rat liver mitochondria or liver slices to oxidize acetaldehyde. Any inhibition of ALDH resulted in a decreased rate of acetaldehyde oxidation, indicating that there is no excess of ALDH in the cell above what is needed to oxidize acetaldehyde. Approximately 15% of the acetaldehyde disappearance at 200 microM was catalyzed by high-Km ALDH, and nearly 30% of the acetaldehyde was lost through binding to cytosolic proteins.     

Elevation by ethanol and its metabolites of liver adenosine monophosphate

Acute ethanol administration significantly increased the concentration of adenosine monophosphate (5'-AMP) in the intact freeze-clamped rat liver regardless of the ethanol dose administered. The increase was abolished by the alcohol dehydrogenase inhibitor 4-methylpyrazole, but was also seen after direct infusion of acetaldehyde into the portal vein. Administration of acetate to give hepatic levels similar to those seen during ethanol oxidation failed, however, to cause an increase in AMP. After ethanol administration there was a highly significant positive correlation between individual AMP levels and 3-OH-butyrate/acetoacetate ratios. The results suggest that the increase in liver AMP reflects activation of ethanol-derived acetate by acetothiokinase in the mitochondrial matrix. Ethanol, but not acetate inhibits the citric acid cycle, as reflected by the shift in the mitochondrial redox state. This could inhibit production of GTP needed for AMP phosphorylation by GTP-AMP phosphotransferase, thus explaining the accumulation of AMP by ethanol.     

Studies on the response of isolated rat liver mitochondria to polychlorinated biphenyls (Kanechlors®)

A comparative study was made of the effects of biphenyl and polychlorinated biphenyls (Kanechlors^®, KCs) on the respiratory and energylinked activities of rat liver mitochondria. With ketoglutarate/malate as the substrate, biphenyl acted as the strongest inhibitor of state 3 respiration. The inhibition of state 3 respiration was decreased as chlorine content increased. The stimulation of state 4 respiration was greatest in KC-200, 300, and 400; intermediate in biphenyl and KC-500; least in KC-600. When succinate was the substrate, from the results of this and a previous study (Nishihara 1983) the action of biphenyl as an inhibitor of state 3 respiration was least effective. The inhibitory action on state 3 respiration was strengthened by the chlorination of aromatic rings (KC-200), reaching a peak where maximum inhibition was observed (KC-300, 400, and 500), further increases in chlorine content (KC-600) repressed the inhibitory action. The stimulating ability of state 4 respiration was greatly diminished with increases in chlorination. Biphenyl and KCs induced the K⁺ -release from mitochondria, thereby dissipating membrane potential across the mitochondrial membranes in the order; biphenyl > KC-200 > KC-300 > KC-400 > KC-500 > KC-600. It is concluded that with -ketoglutarate/malate (NAD⁺ -linked substrate), KCs act as uncouplers by increasing the permeability of mitochondrial inner membranes to ions, and that when succinate is the substrate, KCs act as inhibitors rather than uncouplers of oxidative phosphorylation of mitochondria by inhibiting the electron transport chain.     

Uncoupling action of polychlorinated biphenyls (Kanechlor ®-400) on oxidative phosphorylation in rat liver mitochondria

A study was made of the uncoupling action of polychlorinated biphenyls (Kanechlor®-400) on oxidative phosphorylation in rat liver mitochondria. Kanechlor-400 (KC-400) at 20 g/ml stimulated state 4 respiration of rat liver mitochondria more than 4-fold with-ketoglutarate/malate as a substrate, and released the oligomycin-inhibited state 3 respiration. KC-400 also dissipated the membrane potential across the mitochondrial membranes; thus, it acts as an uncoupler of oxidative phosphorylation in rat liver mitochondria. KC-400 altered the permeability properties of mitochondrial membranes as evidenced by the release of endogenous K⁺ and the oxidation of exogenously supplied NADH. It is concluded that KC-400 produces a nonspecific increase in mitochondrial ion permeability, thereby dissipating membrane potential, which leads to the uncoupling.     

Uptake of 5-formyltetrahydrofolate in isolated rat liver mitochondria is carrier-mediated.

We have characterized the uptake of 5-formyltetrahydrofolate into isolated rat liver mitochondria. Uptake of 5-formyltetrahydrofolate, 5-methyltetrahydrofolate and folic acid was linear for the first 2 min of incubation. 5-Methyltetrahydrofolate and 5-formyltetrahydrofolate were accumulated in mitochondria to 3.7- and 4.3-fold, respectively. 5-Formyltetrahydrofolate transport showed a pH optimum at 5.5 and was saturable with an apparent Km = 2.80 mumol.L-1 and Vmax = 3.49 pmol.min-1.mg protein-1. Uptake of 5-formyltetrahydrofolate was inhibited by the structural analog 5-methyltetrahydrofolate and, to a much lesser extent, folic acid and methotrexate. Uptake was not inhibited by various substrates of known mitochondrial transporters, e.g., succinate, malate, citrate, glutamate and phosphate, nor was uptake inhibited by the sulfhydryl reagent, N-ethylmaleimide. Uptake was not stimulated by preloading of mitochondria with malate or aspartate. Uptake of 5-formyltetrahydrofolate was not affected by the proton ionophore carbonyl cyanide 4-trifluoromethoxyphenyl-hydrazone nor by collapsing the electrical gradient with valinomycin. These results indicate that 5-formyltetrahydrofolate uptake into mitochondria via a carrier-mediated system specific for the reduced, naturally occurring folates. The folates, once in the mitochondria, may be converted to the polyglutamylated forms, which will not readily diffuse out of the mitochondria.     

Studies on mitochondrial metabolic processes in offspring of alcoholized rats--I. Evidence for altered activity and sensitivity to monoamine oxidase-dependent control by biogenic amines of some membrane-bound enzymes.

In the liver mitochondrial fraction of the first generation offspring of alcoholized male rats, decreased activities of monoamine oxidase (MAO) types A and B, rotenone-insensitive NADH-cytochrome c-reductase and succinate dehydrogenase were observed. The MAO-dependent inhibition of rotenone-insensitive NADH-cytochrome c-reductase and succinate dehydrogenase by biogenic amines, incubated with the mitochondrial fraction, was altered in the offspring of alcoholized animals as compared with control rats. The sensitivity of these enzymatic activities towards the inhibitory effect of 5-methoxyindol-3-ylacetaldehyde was markedly increased in the offspring of alcoholized male rats. The data obtained suggest the existence of a genetically determined predisposition of the mitochondrial metabolic processes in the offspring of the alcoholized rats to the effects of ethanol and to the toxic effects of acetaldehyde, formed during ethanol metabolism.     

Interaction of flufenamic acid on ethanol metabolism in rat.

Flufenamic acid (FA) is a widely used non-steroidal anti-inflammatory drug. It is also known to be an uncoupling agent of oxidative phosphorylation in mitochondria. The interaction of FA and ethanol has been of concern in the occupational health field, since alcohol consumption is a common habit among members of the working population. Thus, we investigated the effects of FA on ethanol metabolism in the rat. In the first experiment, FA and ethanol were administered intragastrically to male Wistar rats. Ethanol and acetaldehyde were measured in blood samples collected from the tail vein by head-space gas chromatography. In the second experiment, the interaction of FA and ethanol was observed in the perfused rat liver. The following items were monitored in perfused livers from both fed and fastd rats: uptake rate of ethanol, production rate of acetaldehyde, level of reduced pyridine nucleotides, and oxygen consumption rate. In the first experiment, the rats with FA showed significantly higher concentrations of both ethanol and acetaldehyde in blood after ethanol intake than the rats without FA. In the perfused liver, FA suppressed ethanol uptake, and increased acetaldehyde concentration in the effluent. FA decreased the level of intracellular reduced pyridine nucleotides which had been elevated by ethanol. FA caused an increase in the oxygen consumption rate, which was not altered by the coexistence of ethanol. It was concluded that FA suppressed ethanol metabolism due to suppression of acetaldehyde oxidation in the liver, despite its uncoupling effect on oxidative phosphorylation in mitochondria.     

Hepatic mitochondrial and peroxisomal oxidative capacity in riboflavin deficiency: effect of age, dietary fat and starvation in rats

The effects of riboflavin deficiency on mitochondrial and peroxisomal substrate oxidation were examined in young (treatment begun at weaning) and adult Sprague-Dawley rats that were fed diets low and high in fat. State 3 respiration rates (ADP-stimulated) were used as an estimate of mitochondrial oxidation rates. The oxidation of palmitoyl-CoA and palmitoylcarnitine, and to a lesser extent, glutamate, pyruvate and succinate, by hepatic mitochondria isolated from the young rats was depressed with riboflavin deficiency. There was no effect of dietary fat level on mitochondrial substrate oxidation. Carnitine palmitoyltransferase-A (CPT-A) Vmax was increased with riboflavin deficiency and with increasing dietary fat. Cyanide-insensitive palmitoyl-CoA oxidation was used to estimate peroxisomal palmitate oxidation. Expressed as total hepatic capacity, peroxisomal palmitate oxidation was depressed with riboflavin deficiency. This effect was the result of the reduced feed intake rather than riboflavin deficiency per se. Increasing dietary fat resulted in increased peroxisomal palmitate oxidation. Starvation of young rats did not change mitochondrial oxidation rates, although riboflavin-deficient starved rats exhibited increased rates of palmitoyl-CoA oxidation as well as increased CPT-A Vmax. In adult rats, after 5 wk of deficiency, only palmitoyl-CoA and palmitoylcarnitine oxidation rates were depressed. Dietary fat level did not interact with riboflavin deficiency. However, CPT-A Vmax was increased with riboflavin deficiency and with increased dietary fat level. Further, depressed hepatic fatty acid oxidation can occur in adult rats as a sequel to the feeding of riboflavin-deficient diets.     

A Review of the Effects of Alcohol on Carbohydrate Metabolism

1. The effects of alcohol (ethanol) on carbohydrate metabolismare reviewed. 2. The metabolism of ethanol by alcohol dehydrogenaseleading to a decreased [NAD+]/[NADH] ratio plays an importantrole in the above effects of ethanol in the liver, whereas effectsin brain and other tissues could be caused by acetaldehyde transportedfrom the liver. 3. Ethanol increases peripheral acetate utilizationand decreases free coenzyme A in brain. 4. Ethanol inhibitshepatic gluconeogenesis by decreasing the steady-state concentrationof pyruvate. 5. Ethanol inhibits glycolysis in liver and brain.In the liver, the inhibition may be at the level of 3-glyceraldehydephosphate dehydrogenase. 6. Ethanol inhibits the tricarboxylicacid cycle by an undefined mechanism(s) involving decreasedpyruvate concentration, increased malate/oxaloacetate ratioor inhibition of citrate synthase and isocitrate dehydrogenase.7.Ethanol inhibits the pentose phosphate pathway in the liver,but enhances that in the brain. The mechanisms of these actionsrequire investigation. 8. Ethanol causes an initial hyperglycaemia,a later hypoglycaemia and various effects on glucose utilization.9. Ethanol inhibits galactose metabolism by inhibiting the keyenzyme uridine diphosphate galactose 4-epimerase. 10. Ethanolinhibits the metabolism of fructose and sorbitol. 11. It issuggested that further work is required to examine the rolesof acetaldehyde and of pyridine nucleotides in the actions ofethanol on brain carbohydrate metabolism.     

Effect of naphthalene on respiration in heart mitochondria and intact cultured cells

Mitochondrial respiration is inhibited 50% by 10 ppm (78 μm) naphthalene. NADH oxidase, NADH-cytochrome c reductase, ubiquinone-50 oxidase, and NADH-ubiquinone reductase are inhibited, while succinate oxidations, NADH-ferricyanide reductase, NADH-indophenol reductase, and ATPase activities are not inhibited. The $\text{ADP}\text{O}$ ratio of coupled mitochondria is not decreased. Inhibition of respiration occurs at the level of coenzyme Q. Oxygen consumption of intact cultured cells is also inhibited by naphthalene as in isolated mitochondria. Exposure to naphthalene at concentrations greater than 7.5 ppm causes cultured cells to round up and release from the flask surface, with eventual death the result. The effects of naphthalene on morphology and respiration are very similar, suggesting that mitochondrial inhibition plays a significant role in effects of naphthalene on intact cells.