Reaction of deamination of monoamines in the brain and heart of rats under the toxic action of hyperbaric oxygenation

Kinetic parameters of monoamine deamination processes in the rat brain and heart after hyperbaric oxygenation (HBO) in toxic conditions (6 ata) were studied. HBO was shown to cause a substantial reduction in MAO affinity to serotonin in the brain, but not in the heart. Contrastingly, MAO affinity to dopamine was found to decrease in the heart, but not in the brain in response to HBO. Differences of tyramine and 2-phenylethylamine deamination in the rat brain and heart were also reciprocal following toxic HBO. In the initial phase of seizure episode MAO activity in the brain and heart was also different. Distinct mechanisms of adaptation to toxic oxygen in the central nervous system and cardiovascular system are discussed.     

Changes in the balance of biogenic monoamines and their metabolites in the organs of rats with oxygen-induced epilepsy

The content of some biogenic monoamines and their metabolites in rat brain and heart in different periods of oxygen epilepsia was studied using high performance liquid chromatography with electrochemical detection. It was shown that already at the 5th minute of exposure to oxygen adrenaline, DOPA and some noradrenaline metabolites disappeared in the brain and noradrenaline level reduced. At this period in rat heart the reduction of catecholamine content was the most distinct and serotonin level was unchanged. At the beginning of convulsive period the modifications of biogenic amines content were nonparallel in brain regions: in the heart the reduction of catecholamine level went on, especially in right ventricle. In the terminal phase of oxygen epilepsia brain biogenic amines increased, however, not up to normal meaning, heart catecholamines at this period were at the same level as at the beginning of the convulsive period.     

Effect of prolonged cold exposure on monoamine oxidase activity and kinetics and on serotonin metabolism in the rat brain

Effects of long-term cold exposure on the content of serotonin and its metabolite 5-hydroxyindolacetic acid (5-HIAA) and monoamine oxidase (MAO) activity and kinetic parameters (Km and Vmax) of oxidative deamination of serotonin in rat brain stem. The increase of 5-HIAA level in the initial period of chronic cold exposure was determined by the blockade of active metabolite transport from the brain. The level of serotonin and the rate of its catalytic deamination by MAO were found to be decreased in cold-adapted rats. The magnitude of the Km of serotonin deamination was unchanged.     

Neuromediator mechanisms of the effect of the antihistamine agent dimebone on the brain

Dimebone was shown to inhibit monoamine oxidase (MAO) deaminating dopamine and serotonin, decrease dopamine metabolism in the basal ganglia of the rat brain, increase noradrenaline level and depress dopamine deamination in the hypothalamus. Dimebone first increased and then diminished the release of dopamine in the cortex, with the concomitant MAO activation and the increase in dopamine and noradrenaline levels. The in vitro experiments have demonstrated that dimebone (10(-4)) preferentially inhibited MAO activity, type B and dopamine deamination in homogenates of different rat brain structures. The role of MAO inhibition in the mechanism of dimebone action on the catecholamine metabolism in the brain structures and its stimulating effect on CNS are discussed.     

Change in serotonin metabolism in the rat brain in response to the repeated stimulus presentation

The content of serotonin (5-HT), its metabolite 5-hydroxyindoleacetic acid (5-HIAA), monoamine oxidase (MAO) activity and kinetic parameters (K(m) and Vmax) for the reaction of 5-HT deamination, were examined in various regions of the rat brain after repeated presentation of a contextual stimulus. Habituation to the stimulus was accompanied by an increase of 5-HT metabolism and active transport of 5-HIAA in the amygdala, striatum and midbrain, while these changes were not found in the prefrontal cortex and hippocampus. Kinetic studies have revealed that the enhancement of 5-HT deamination by MAO in the brain structures was mediated by different catalytic mechanisms. A significant decrease in K(m) value for 5-HT deamination in the amygdala indicated an increase in the affinity of enzyme towards 5-HT. In the striatum the enhanced MAO activity was provided by increasing maximal rate of 5-HT deamination. It is concluded that an activation of presynaptic mechanisms of the serotonergic transmission in the amygdala and striatum is involved in the inhibition of biological significance and attention to repeated presentation of stimulus.     

THE EFFECTS OF CHRONIC REGIMENS OF CLORGYLINE AND PARGYLINE ON MONOAMINE METABOLISM IN THE RAT BRAIN

The effects of chronic administration of clorgyline and pargyline on rat brain monoamine metabolism have been examined. The inhibitory selectivity of these drugs towards serotonin deamina-tion (MAO type A) and phenylethylamine deamination (MAO type B) can be maintained over a 21-day period by proper selection of low doses of these drugs (0.5-1.0 mg/kg/24h). The results are consistent with MAO type A catalyzing the deamination of serotonin and norepinephrine and with MAO type B having little effect on these monoamines. Dopamine appears to be dcaminated in vivo principally by MAO type A. Clorgyline administration during a 3-week period was accompanied by persistent elevations in brain norepinephrine concentrations; serotonin levels were also increased during the first 2 weeks, but returned towards control levels by the third week of treatment. Low doses of pargyline did not increase brain monoamine concentrations, but treatment with higher doses for 3 weeks led to elevations in brain norepinephrine and 5-hydroxytryptamine; at this time significant MAO-A inhibition had developed. The changes in monoamine metabolism seen at the end of the chronic clorgyline regimen are not due to alterations in tryptophan hydroxylase activity. At this time tyrosine hydroxylase activity was also unaffected.     

Adaptation of brain monoamine synthesis to hypoxia in the rat.

Oxygen is a substrate in the synthesis of the neurotransmitters, norepinephrine, dopamine, and serotonin. Changes in environmental oxygen appear to cause corresponding alterations in brain monoamine synthesis in vivo. The effect of chronic hypoxia was studied by exposing rats to 10% oxygen for up to 36 h. Brain monoamine synthesis, estimated in vivo, decreased initially and then returned to control levels, despite continued exposure to 10% oxygen. During this apparent adaptation to hypoxia, there were no changes in the concentration of brain serotonin, norepinephrine, dopamine, or tryptophan, while brain tryosine increased after 24 h of exposure. Tyrosine hydroxylase activity in vitro was not altered by the exposure to 10% oxygen. Evidence of hypoxic adaptation in these rats, a rightward shift of their hemoglobin dissociation curves, was found after 24 h of exposure. The adaptation of brain monoamine synthesis to hypoxia appeared to correlate with adaptive changes in brain tissue oxygen rather than any change in the intraneuronal regulation of amine synthesis.     

Multiplicity of monoamine oxidase: inhibition of mitochondrial monoamine oxidase activity by isopropylhydrazide of D,L-serine]

Isopropylhydrazide of D,L-serine (IHS) inhibits by 50% (at 37 degrees for 10 min) deamination of serotonin or beta-phenylethylamine by monoamine oxidases from bovine brain stem mitochondrial membranes at the 2.6 X X 10(-5) M or 9 X 10(-5) M, respectively. In order to inhibit by 50% the deamination of tyramine under the same conditions a considerably lower (2.5 X X 10(-6) M) concentration of IHS is required. Kinetic studies of inhibition of enzymatic deamination of all the three biogenic monoamines by IHS showed that the irreversible blocking of the monoamine oxidase activity is preceeded by formation of dissociating enzyme-inhibitor complexes. Values of the dissociation constants of these complexes measured (at 37 degrees) with serotonin, phenylethylamine or tyramine as substrates for estimation of the residual monoamine oxidase activity are 0.47; 0.13 or 0.023 mM, respectively. Significant differences are also found between thermodynamic and activation parameters characterizing both both steps of interaction between IHS and the monoamine oxidases of mitochondrial membranes in the experiments with serotonin, phenylethylamine or tyramine as substrates. The data obtained suggest the existence of different monoamine oxidases (or their active sites) catalyzing oxidative deamination of serotonin, phenylethylamine or tyramine in the fragments of mitochondrial membranes from bovine brain stem.     

Effect of benzamide derivatives on convulsions induced by the toxic action of oxygen in rats

The reversible MAO-A inhibitor moclobemide (5 mg/kg) was shown to prevent seizures in rats during exposure to toxic oxygen (6 ata). Benzamide derivatives increased the latent period of oxygen seizures and decreased the lethality following hyperbaric oxygenation. The range of anti-MAO activity of moclobemide and clorgyline in the rat brain and heart after toxic oxygenation was studied. It was distinct from those in control animals. Clorgyline was found to be more active in inhibiting MAO during toxic oxygenation in the heart and moclobemide-in the brain. The possibility is shown to prevent oxygen seizures not only with irreversible MAO-A inhibitors (clorgyline), but also with reversible ones (moclobemide).     

Monoamine oxidase activity of rat brain under cold exposure

Cold stress and cold adaptation were studied for their effect on the activity and substrate specificity of the monoamine oxidase A and B and on the Km of serotonin deamination in the rat brain mitochondria and supernatant. Mitochondrial monoamine oxidase Km with serotonin is established to increase more than twice under cold stress and decrease considerably in cold adapted rats. The lowering of the mitochondrial monoamine oxidase A activity is accompanied by the appearance of serotonin and the glucosamine deaminating activity in supernatant. The data suggest that decrease in the monoamine oxidase activity under cold stress may be caused by both release of the enzyme from mitochondrial membrane and changes in its catalytic property alteration.     

Effect of benzamide derivatives on rat brain monoamine oxidase activity in vitro

The ability of moclobamide and other benzamide derivatives to inhibit the activity of monoamine oxidase in the rat brain was studied. Distinct effects of these compounds on the deamination of serotonin and norepinephrine (MAO-A substrates); 2-phenylethylamine (selective MAO-B substrate); tyramine and dopamine (MAO-A and MAO-B substrates) are shown. It was demonstrated that among all the compounds studied moclobamide appeared to be the most active and selective inhibitor of MAO-A: at a concentration of 100 microM it caused a 100% inhibition of serotonin and norepinephrine deamination, which might be explained by the presence of C1 atom in the para-position of benzene ring in moclobamide molecule. Other benzamide derivatives were less active in inhibiting MAO-A and had but a negligible effect on dopamine- and 2-phenylethylamine deamination.     

Chlorphentermine inhibits pulmonary mitochondrial monoamine oxidase

Oxidation of six amine substrates by rat, rabbit and guinea-pig lung mitochondrial monoamine oxidase (MAO) was investigated polarographically with a Clark oxygen electrode in the presence of chlorphentermine (CP). This amphiphilic drug decreased the deamination of serotonin, norepinephrine, tyramine and dopamine significantly in all three species. However, the oxidation of tryptamine and benzylamine was unchanged. Amine oxidation by MAO in guinea-pig lung mitochondria was much more sensitive to the CP-mediated inhibition than rat or rabbit. A kinetic study of serotonin oxidation in the absence and presence of CP showed that both Vmax and Km were affected. These combined data indicate that CP is a specific inhibitor of pulmonary, mitochondrial monoamine oxidase form A with mixed-type inhibition.     

Inhibition of noradrenaline deamination by antidepressants

Anti-norepinephrine deaminative activity of some antidepressants of different structure was studied. Pyrazidol (10(-5) M) reduced considerably the rate of norepinephrine deamination in bovine brain (80% inhibition), the inhibitory effects of inkazan and imipramine were also apparent (50-60%). Zimelidine, viloxazine and norzimelidine were found to be less active: at 10(-4) M, they caused a not more than 50% inhibition of oxidative norepinephrine deamination. The difference was revealed between the influence of some drugs on deamination of two monoamine oxidase A substrates: norepinephrine and serotonin. Thus, pyrazidol, viloxazine, zimelidine and norzimelidine were more active in suppressing norepinephrine, than serotonin deamination. Inhibition of norepinephrine deamination in the brain seems to be an important component of the neurochemical spectrum of pyrazidol and imipramine.     

Inhibition of Monoamine Oxidase by 7-Chloro-4-Nitrobenzofurazan

7-Chloro-4-nitrobenzofurazan (NBD-Cl) is a potent inhibitor of both types of monoamine oxidase (MAO). NBD-Cl competitively inhibited the oxidative deamination of kynuramine catalyzed by human placenta MAO-A, the oxidative deamination of benzylamine catalyzed by bovine liver MAO-B, the oxidative deamination of serotonin catalyzed by rat brain MAO-A, and the oxidative deamination of phenylethylamine catalyzed by rat brain MAO-B. In addition, a time-dependent inactivation of MAOs by NBD-Cl has been demonstrated upon incubation of the enzyme preparations with NBD-Cl at pH 9, but not at pH 7.5. The time-dependent inhibition of MAO by NBD-Cl could be prevented by the addition of 4-nitrophenyl azide, an active site-directed label of MAO, during incubation of the enzyme with NBD-Cl. On the basis of these findings, it is suggested that at pH 9, NBD-Cl modifies one (or more) essential lysine residue(s) in the active sites of the two types of MAO.     

Difference in monoamine oxidase activity measured by either liquid ion exchange or ion exchange resin chromatography in rat and cat brain

Cat and rat brain monoamine oxidase (MAO) activity was measured with a radioisotopic procedure and two extraction methods. Results indicated an underestimation of MAO activity when liquid ion exchange chromatography (LIEC) was used instead of an ion exchange chromatographic method (IEC) to separate the different products of the deaminated tyramine, phenylethylamine, or serotonin. MAO produced aldehydic products which may be found in the incubation medium and may be extracted with the substrate in the chloroform phase by the LIEC method. In cat brain, the resulting underestimation of the MAO activity was prevented by the addition of nicotinamide adenine dinucleotide (10(-3) M) in the incubation medium or by allowing a 2-h period between the end of incubation and the LIEC extraction procedure. In the rat brain, the same result was obtained by the addition of an equimolar mixture of nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate in reduced form (NAD-NADPH, 10(-3) M). Using the IEC method, the NAD decreased only the deamination of tyramine and serotonin in rat brain. This study suggests that the use of an IEC method to evaluate MAO activity is more accurate for the estimation of the enzymatic activity.     

Disorders of the deamination of nitrogenous compounds in the heart muscle in experimental atherosclerosis

The development of alimentary hypercholesterolemia in rabbits (confirmed by morphometric, electrophysiological and biochemical data) was accompanied by a decrease of the serotonin, benzylamine and tyramine deamination rates in heart muscle mitochondria. At the same time a qualitatively new reaction of cadaverine deamination could be seen in the mitochondria. The data obtained suggest that impairment of deamination of the nitrogenous compounds in atherosclerosis may be due to reversible qualitative modification (transformation) of mitochondrial monoamine oxidase activity. Some of the drugs which decrease the level of lipids in blood serum of hypercholesterolemic rabbits abolished and prevented the impairment of deamination of nitrogenous compounds.     

Changes in brain monoamine oxidase activity in conditioned passive avoidance reaction in rats]

Activity of the enzyme monoamine oxidase (MAO) and kinetic parameters (Km, Vmax) for the 5-hydroxytryptamine (5-HT) and dopamine deamination were examined in the brain of rats with conditioned passive avoidance recall. Changes of the 5-HT and dopamine deamination were found in amygdala, striatum and frontal cortex. MAO activity was not changed in hippocampus. In amygdala the rate of 5-HT deamination was significantly increased and kinetic studies revealed increased affinity of the enzyme for 5-HT. The metabolism of dopamine in amygdala was unchanged. In frontal cortex the deamination of 5-HT was not changed, but the dopamine deamination significantly decreased. This decrease was due to lowering of MAO affinity for dopamine. In striatum the metabolism of both 5-HT and dopamine was reduced, and kinetic studies showed the lowering of Vmax for 5-HT and dopamine deamination.     

Conjugated dinitrocompound dianions as inhibitors of the oxidative deamination of monoamines

The conjugated derivatives--1.4-dinitrobutene-2, 1,4-dinitro-2-methylbutene-2, 1,4-dinitro-2,3-diphenylbutene-2 sodium salts, as well as dinitromethane sodium salt and beta-nitrostyrol, the inhibitors of oxidative deamination of serotonin, tyramine, tryptamine and benzylamine in bovine liver mitochondria, were studied. All the derivatives under study were found to be active inhibitors of monoamine oxidase catalyzing the oxidative deamination of serotonin, tyramine and tryptamine. In a far lesser degree these preparations inhibited the deamination of benzylamine, a specific substrate for monoamine oxidase B. All the dinitrocompound dianions, with the exception of 1,4-dinitro-2,3-diphenylbutene-2 disodium salt, a non-competitive inhibitor of oxidative deamination of the four substrates under study, cause competitive reversible inhibition of monoamine oxidase.     

Deamination of Aliphatic Amines by Monoamine Oxidase A and B Studied Using a Bioluminescence Technique

Deamination of n-octylamine and n-decylamine has been studied in various tissues using a new bioluminescence technique. Selectivity of n-octylamine and n-decylamine as substrates for monoamine oxidase (MAO) A or B has been determined using both clorgyline and (-)-deprenyl inhibition curves and kinetic parameters. Homogenates of rat brain, liver and heart containing predominantly MAO-A or -B were prepared by preincubation for 60 min with (-)-deprenyl or clorgyline (30 nM), respectively. Human placenta (MAO-A) and platelet (MAO-B) were used as reference tissues containing only one MAO form. In tissues (rat liver, brain) containing both MAO forms in equal proportion, inhibition curve studies showed a preference of both substrates for the B form of the enzyme; however, where MAO-A was the major form (rat heart, human placenta), clorgyline was the more effective inhibitor. In the beef brain cortex n-octylamine showed marked preference for MAO-B, whereas n-decylamine was selective toward-MAO-A. Kinetic studies in general supported the picture of greater selectivity of the aliphatic amine substrates for deamination by MAO-B, as reflected by lower Km values for this enzyme type. However, n-octylamine was more selective for MAO-B than n-decylamine in both kinetic and inhibition curve studies. The deamination of these aliphatic amine substrates cannot be explained only by reference to the binary classification of MAO into types A and B.     

Disorders of the dynamics of postnatal development of monoamine oxidase activity in the brain as affected by the antenatal action of alcohol

The activity of different types of monoamine oxidase (MAO)-MAO, type A (substrate serotonin) and two types of mixed MAO forms using tyramine or dopamine as substrates, in different brain regions of the rat offspring exposed prenatally to ethanol was investigated on the 30th and 60th day postnatally. The present study has revealed differences in the development of brain MAO activity during ontogenesis. Disturbances in the activity of all MAO types investigated as well as the distortion of their postnatal development have been observed in the brain of the rat offspring exposed prenatally to ethanol. The possible teratogenic effect of ethanol on the developing fetal brain is discussed.