Comparison of the effects of ammonia on brain mitochondrial function in rats and gulf toadfish

We compared the effect of hyperammonemia on NADH levels in brain slices and on the rate of oxygen consumption from isolated nonsynaptic brain mitochondria in ammonia-sensitive Wistar rats with that in ammonia-tolerant gulf toadfish (Opsanus beta). The NADH content was significantly decreased (12% less than control after 45 min with 1 mM NH(4)Cl) in rat brain slices, but it was not affected in brain slices from toadfish (with both 1 and 6 mM NH(4)Cl). The rates of oxygen consumption of different sets of enzymes of the electron transport chain (ETC; complexes I, II, III, and IV; II, III, and IV; and IV alone) were unaltered by hyperammonemic conditions in isolated nonsynaptic mitochondria from either rats or toadfish. These results lead us to conclude that the differing effects of ammonia on NADH levels in rat and toadfish brain slices must be due to aspects other than the direct effects of ammonia on enzymes of the ETC. Additionally, because these effects were seen in vitro, our studies enabled us to rule out the possibility that effects of ammonia on metabolism were via indirect systemic effects. These results are discussed in the context of current views on mechanisms of central nervous system damage in hyperammonemic states.     

Intestinal ammonia metabolism in ethanolic rats

Repeated treatment of ethanol for 5 consecutive days has produced significant biochemical changes in the small intestine of the rat. The LDH and SDH were inhibited leading to deficient energy output from the glycolytic pathway and the Krebs cycle. The changes in ammonia metabolic profiles of intestine and blood indicate the presence of hyperammonemia. Enzymatic reactions associated with urea production and the levels of urea were increased. GS activity decreased explaining low levels of glutamine. These studies implicate PNC in producing hyperammonemia during ethanol treatment.     

Discontinuation effects of oxazepam and diazepam treatment on brain GABA metabolism in rats

The effects of oxazepam and diazepam (both at 10 mg/kg, i.p.) during continuous treatment for 15 days and following discontinuation after 5 days onwards on cerebral glutamic acid decarboxylase (GAD) and GABA-aminotransferase (GABA-T) have been studied. It has been found that during continuous treatment as well as following discontinuation after 5 days, a significant increase in GAD activity is observed in case of diazepam but not in case of oxazepam. On the other hand, a marked decrease in GABA-T activity is observed during continuous treatment up to 15 days with both diazepam and oxazepam but during discontinuation phase, the decreased GABA-T activity tends to increase and attain normal value much earlier in case of oxazepam than diazepam. This differential effect of oxazepam and diazepam on γ-aminobutyric acid (GABA) metabolism, following discontinuation of treatment, may possibly contribute to the difference in withdrawal effects associated with the two benzodiazepines.     

Silymarin improves metabolism and disposition of aspirin in cirrhotic rats

The profile of urinary salicylate metabolites was determined after an i.p. administration of acetylsalicylic acid (ASA) to CCl4-cirrhotic rats to rats which in addition to CCl4 received an oral dose of silymarin throughout the CCl4 treatment to produce cirrhosis and to control groups. ASA esterase activity was determined in serum and livers. The time course of plasma concentration of salicylates in similar groups was followed after the i.p. injection of ASA. The cirrhotic animals showed a lack of urinary glucuronides and an increase in urinary gentisic and salicylic acids. The activities of plasma and serum ASA esterase were significantly increased in cirrhosis and the plasma half-life of ASA was reduced. The simultaneous administration of silymarin (50 mg/kg of b.w.) along with CCl4, completely prevented all the alterations. The mechanism by which silymarin prevented those alterations is not completely known but our results establish the potential use of silymarin in cirrhotic patients to prevent disorders in drug metabolism and disposition frequently found in patients with liver diseases.     

Regionally specific effects of diazepam on brain serotonin metabolism in rats: Sustained effects following repeated administration

The effects of single (1mg/kg) and repeated (1mg/kg 2¹ daily for 4 days) diazepam administration are investigated on brain regional 5-hydroxytryptamine (5-HT; serotonin) and 5-hydroxy indoleacetic acid (5-HIAA) concentration in rats. Daily treatment decreased food intakes but body weights did not decrease. Administration of diazepam (1mg/kg) to 4 day sahne injected rats on the 5th day decreased 5-HT levels in the hippocampus and increased it in the hypothalamus. 5-HIAA levels were increased in the striatum and decreased in the hypothalamus. 4 day diazepam injected rats injected with sahne on the 5th day also exhibited silmilar changes of 5-HT and 5-HIAA. Cortical levels of 5-HIAA were also smaller in these rats. Administration of diazepam to 4 day diazepam injected rats again decreased 5-HT in the hippocampus and 5-HIAA in the hypothalamus. 5-HT and 5-HIAA were both decreased in the striatum. Regionally specific effects of diazepam on brain serotonin metabolism are discussed in relation to their possible functions.     

Hemodynamic effects of Salvia miltiorrhiza on cirrhotic rats

Salvia miltiorrhiza (Sm) administration has been shown to reduce hepatic fibrosis in rats. We investigated the hemodynamic effects of Sm on bile duct ligated (BDL) rats. Hemodynamic, histological, and vascular contractile studies were conducted in rats 4 weeks after bile duct ligation. An aqueous extract of Sm (0.2 g twice per day) or vehicle was administered for 4 weeks to BDL rats. Sm treatment in BDL rats significantly reduced histological grades of fibrosis and ameliorated the portal hypertensive state (including portal venous pressure, superior mesenteric artery blood flow, cardiac index, and total peripheral resistance) as compared with vehicle treatment. Moreover, Sm treatment enhanced the vascular sensitivity of mesenteric arteries to phenylephrine in BDL rats. Sm treatment had no effect on plasma biochemical profiles of either BDL or normal rats. Our results suggest that 4-week Sm treatment ameliorates the portal hypertensive state in BDL rats.     

Effects of dieldrin, picrotoxin and Telodrin on the metabolism of ammonia in brain

1. Increases in the concentrations of lactic acid and pyruvic acid in rat brain during acute dieldrin poisoning are associated with hyperactivity of the brain, whereas an increase in the cerebral alanine concentration occurs before the convulsions. Throughout the dieldrin-induced seizure pattern, fluctuations in the concentration of brain ammonia are out of phase with the actual convulsions. 2. Increases in the concentrations of alanine, ammonia and lactic acid in rat brain accompany picrotoxin-induced seizures; there is no increase in the concentration of glutamine. These changes are consistent with the inhibition of glutamine synthesis. 3. In addition to previously reported changes in the concentrations of intermediary metabolites of the brain after the administration of Telodrin (Hathway & Mallinson, 1964), increases have now been found in the alanine and lactic acid concentrations. Since increases in the alanine and glutamine concentrations occur before the convulsions, liberation of ammonia also occurs before the onset of convulsions and throughout their course. Ammonia-binding mechanisms later become inadequate and free ammonia accumulates in cerebral tissues. 4. An increase in the pyruvic acid concentration of the brain after the intraperitoneal injection of either dieldrin or Telodrin is endogenous in origin. 5. The parenteral administration of a small dose of glutamine increases the cerebral concentrations of alanine and glutamic acid. Some animals previously treated with glutamine resisted Telodrin convulsions. 6. Mechanisms for the disposal of ammonia liberated in brain are discussed.     

The acute action of ammonia on rat brain metabolism in vivo

1. Acute NH(4) (+) toxicity was studied by using a new apparatus that removes and freezes the brains of conscious rats within 1s. 2. Brains were removed and frozen 5min after intraperitoneal injection of ammonium acetate (2-3min before the onset of convulsions). Arterial [NH(4) (+)] rose from less than 0.01 to 1.74mm at 4-5min. The concentrations of all glycolytic intermediates measured, except glucose 6-phosphate, were increased by the indicated percentage above the control value as follows: glucose (by 41%), fructose 1,6-diphosphate (by 133%), dihydroxyacetone phosphate (by 164%), alpha-glycerophosphate (by 45%), phosphoenolpyruvate (by 67%) and pyruvate (by 26%). 4. Citrate and alpha-oxoglutarate concentrations were unchanged and that of malate was increased (by 17%). 5. Adenine nucleotides and P(i) concentrations were unchanged but the concentration of creatine phosphate decreased slightly (by 6%). 6. Brain [NH(4) (+)] increased from 0.2 to 1.53mm. Net glutamine synthesis occurred at an average rate of 0.33mumol/min per g. 7. The rate of brain glucose utilization was measured in vivo as 0.62mumol/min per g in controls and 0.81mumol/min per g after NH(4) (+) injection. 8. The arteriovenous difference of glucose and O(2) increased by 35%. 9. No significant arteriovenous differences of glutamate or glutamine were detected. Thus, although much NH(4) (+) was incorporated into glutamine the latter was not rapidly released from the brain to the circulation. 10. Plasma [K(+)] increased from 3.3 to 5.4mm. 11. The results indicate that NH(4) (+) stimulates oxidative metabolism but does not interfere with brain energy balance. The increased rate of oxidative metabolism could not be accounted for only on the basis of glutamine synthesis. We suggest that increased extracellular [NH(4) (+)] and [K(+)] decreased the resting transmembrane potential and stimulated Na(+),K(+)-stimulated adenosine triphosphatase activity thus accounting for the increased metabolic rate.     

Comparison of the effects of volatile anesthetics in varying concentrations on brain energy metabolism with brain ischemia in rats

The effects of varying concentrations and types of volatile anesthetics on neurochemical sequelae of brain ischemia were evaluated in the rat. Rats were assigned to treatment defined by a 3×3 design (anesthetic type and dose) with 5 rats/cell. Each group received halothane, enflurane, or isoflurane 0.5, 1.0, or 2.0 MAC (minimal alevolar concentration). This was followed by preischemic plasma glucose sampling, 5 min hypotension (30 mmHg) and 5 min decapitation cerebral ischemia. Preischemia plasma glucose increased with increasing anesthetic concentration and was highest in the isoflurane groups, varying from a low (±SD) of 7.19±1.79 mol/ml in the 0.5 MAC halothane group to a high of 12.68±3.65 mol/ml in the 2.0 MAC isoflurane group. End-ischemic brain lactate correlated with preischemic plasma glucose (r=0.5, =0.5). We conclude that increasing concentration of volatile anesthesia with iv phenylephrine blood pressure support produces higher levels of plasma glucose and brain lactate with cerebral ischemia.     

Acute metabolic effects of ammonia in mouse brain

Acute effects of intraperitoneal administration of ammonium chloride (200 mg/kg) on Na⁺,K⁺-ATPase and amino acid content of the glutamate family (glutamate, aspartate, alanine, glutamine, and GABA), as well as the enzymes involved in the metabolism of these amino acids, have been studied in the different regions of brain and liver in mice. A significant increase in the activity of Na⁺,K⁺-ATPase was observed in the cerebellum, cerebral cortex, and brain stem. A similar increase in the activity of glutamate dehydrogenase was observed in the brain stem, while a moderate increase in the activity of this enzyme was observed in the cerebral cortex and liver in the mice treated with ammonium chloride. In all three regions of brain, a 50% decrease was observed in the activity of alanine aminotransferase, while the activity of aspartate aminotransferase significantly rose in the brain stem. The activity of glutamine synthetase did not change much in the three regions of brain, and a significant fall was registered in the liver. The activity of tyrosine aminotransferase showed a rise in the cerebellum, brain stem, and in liver. Not much change was observed in the protein content in either brain or liver, whereas there was a 1.5-fold increase in the total RNA content in the liver of the animals treated with ammonium chloride. Under the experimental conditions, there was an increase only in the content of glutamine, of all the amino acids tested, in the cerebral cortex and liver. Similar results were obtained with homogenates of tissues enriched with ammonium chloride (in vitro) for the enzyme systems studied. These results are discussed, and the probable metabolic and functional significance of ammonia in brain is indicated.     

Neuron-astrocyte interactions in the regulation of brain energy metabolism: a focus on NMR spectroscopy

An adequate and timely production of ATP by brain cells is of cardinal importance to support the major energetic cost of the rapid processing of information via synaptic and action potentials. Recently, evidence has been accumulated to support the view that the regulation of brain energy metabolism is under the control of an intimate dialogue between astrocytes and neurons. In vitro studies on cultured astrocytes and in vivo studies on rodents have provided evidence that glutamate and Na(+) uptake in astrocytes is a key triggering signal regulating glucose use in the brain. With the advent of NMR spectroscopy, it has been possible to provide experimental evidence to show that energy consumption is mainly devoted to glutamatergic neurotransmission and that glutamate-glutamine cycling is coupled in a approximately 1 : 1 molar stoichiometry to glucose oxidation, at least in the cerebral cortex. This improved understanding of neuron-astrocyte metabolic interactions offers the potential for developing novel therapeutic strategies for many neurological disorders that include a metabolic deficit.     

Cell-selective effects of ammonia on glutamate transporter and receptor function in the mammalian brain

Increased brain ammonia concentrations are a hallmark feature of several neurological disorders including congenital urea cycle disorders, Reye's syndrome and hepatic encephalopathy (HE) associated with liver failure. Over the last decade, increasing evidence suggests that hyperammonemia leads to alterations in the glutamatergic neurotransmitter system. Studies utilizing in vivo and in vitro models of hyperammonemia reveal significant changes in brain glutamate levels, glutamate uptake and glutamate receptor function. Extracellular brain glutamate levels are consistently increased in rat models of acute liver failure. Furthermore, glutamate transport studies in both cultured neurons and astrocytes demonstrate a significant suppression in the high affinity uptake of glutamate following exposure to ammonia. Reductions in NMDA and non-NMDA glutamate receptor sites in animal models of acute liver failure suggest a compensatory decrease in receptor levels in the wake of rising extracellular levels of glutamate. Ammonia exposure also has significant effects on metabotropic glutamate receptor activation with implications, although less clear, that may relate to the brain edema and seizures associated with clinical hyperammonemic pathologies. Therapeutic measures aimed at these targets could result in effective measures for the prevention of CNS consequences in hyperammonemic syndromes.     

Long-term effects of iron: Zinc interactions on growth in rats

The influence of iron (Fe) on the bioavailability and functional status of zinc (Zn) was studied in young rats using metabolic balances and tissue dosages, which were compared to growth. Diets supplied adequate intakes of Fe (45 and 300 mg/kg diet) and Zn (14 and 45 mg/kg) for 2 mo. Two metabolic balance determinations were performed that were correlated for Zn and Fe during the first and the last weeks of the study. A significant effect of Fe supply, but not of Zn was displayed on Fe absorption; both Fe and Zn diet concentrations had a significant influence on Zn absorption. Fe and Zn organ contents were significantly correlated with the amount absorbed during the two metabolic balances. There was a positive correlation between liver and muscle Fe and Fe absorption, and Fe absorption and muscle Zn, as well as a negative one with liver Zn; a positive correlation was displayed between Zn absorption and Zn organ content. No correlation was found between Zn absorption and Fe tissue content. Growth was correlated with Zn, but not with Fe absorption during both balances. A positive correlation was displayed between growth and Zn liver content, and a negative one with Fe liver content. Care must be taken to give growing subjects balanced diets or supplementation, since the negative interactions between these trace elements are likely to persist as long as the diet is given.     

Chronic metabolic effects of ammonia in mouse brain.

Chronic ammonia toxicity in experimental mice was induced by exposing them for 2 and 5 days to 5 % (v/v) ammonia solution. The enzymes concerned with glutamate metabolism (aspartate-, alanine- and tyrosine aminotransferases, glutamate dehydrogenase and glutamine synthetase) and (Na+ + K+)-ATPase were estimated in the three regions of brain (cerebellum, cerebral cortex and brain stem) and in liver. Glutamate, aspartate, alanine, glutamine and GABA, RNA and protein were also estimated in the three regions of brain and liver. A significant rise in the activity of (Na+ + K+)-ATPase in all the three regions of brain along with a fall in the activity of alanine aminotransferase was noticed. Changes in the activities of other enzymes were also observed. A significant increase in alanine and a decrease in glutamic acid was observed while no change was observed in the content of other amino acids belonging to the glutamate family. As a result of this, changes in the ratios of glutamate/glutamine and glutamate + aspartate/GABA was observed. The results indicated that the brain was in a state of more depression and less of excitation. Under these conditions the liver tissue was showing a profound rise in the activity of the enzymes of glutamate metabolism. The results are further discussed.     

Effects of ammonia on monoamine oxidase and enzymes of GABA metabolism in mouse brain.

Acute and chronic ammonia toxicity was produced in the mice by intraperitoneal injection of ammonium chloride (200 mg/kg) and by exposure of mice to ammonia vapours (5% v/v) continuously for 2 days and 5 days respectively. The ammonia content was elevated in the cerebellum, cerebral cortex and brain stem and in liver. In acute ammonia intoxication there was a decrease in the monoamine oxidase (MAO) activity in all the three regions of brain. In chronic ammonia toxicity (2 days of exposure) a significant increase in the activity of MAO was observed in the cerebral cortex while in cerebellum and brain stem there was a significant decrease. In cerebral cortex and cerebellum there was a rise in the activity of MAO as a result of exposure to ammonia vapours for 5 days. A significant decrease was observed in the activity of glutamate decarboxylase (GAD) in all the three regions of the brain both in acute and chronic ammonia toxicity (2 days). There was a decrease in the activity of this enzyme only in the cerebral cortex in the animals exposed to ammonia for 5 days. The activity of GABA-aminotransferase (GABA-T) showed a significant rise in cerebellum and a fall in the brain stem in acute ammonia toxicity. In chronic ammonia toxicity GABA-T showed a rise in all the three regions of brain. Chronic ammonia toxicity produced a significant decrease in the content of glutamate in all the three regions without a significant change in the content of aspartate. GABA and glutamine. The content of alanine increased in all the three regions of brain under these experimental conditions. The ratio of glutamate + aspartate/GABA and glutamate/glutamine showed a decrease in all the three regions as a result of ammonia toxicity.     

Galanin-like peptide in the brain: effects on feeding, energy metabolism and reproduction

The hypothalamus plays an important role in the regulation of feeding behavior, energy metabolism and reproduction. A novel peptide containing 60 amino acid peptide and a non-amidated C-terminus is produced in the hypothalamic arcuate nucleus (ARC) and has been named galanin-like peptide (GALP) on the basis of a portion of this peptide being homologous with galanin. It acts in the central nervous system (CNS), where it is involved in the regulation of feeding behavior. GALP-producing neurons make neuronal networks with several feeding related peptide-producing neurons. Since GALP is involved in the control of food intake and energy balance, it is possible that it plays an important role in the development of obesity. Furthermore, GALP regulates plasma lateral hypothalamus (LH) levels via the activation of gonadotropin-releasing hormone (GnRH)-producing neurons, suggesting that GALP is active in the reproductive system. Thus, interesting findings on the roles of GALP have made across a number of physiological systems. This review will attempt to summarize the research carried out to date on these areas. Because GALP may be involved in feeding behavior, energy metabolism and reproduction, further studies on the morphology and function of GALP-containing neurons in the CNS should increase our understanding of the role of GALP in brain function.