Dose-dependent decrease in rat plasma amino acids after acute administration of ethanol

Male rats were given three different doses of ethanol in i.p. injections (0.66, 1.33 and 2.00 g kg-1). A dose-dependent decrease in the concentrations of most plasma amino acids was observed. For the total amino acid concentration this decrease was 5, 16 and 22%, respectively, compared with a saline-treated control group. It has previously been suggested that the oxidation of ethanol plays an important role in the amino acid decreasing effect of ethanol. In this study the lowest dose used (0.66 g kg-1) was calculated to be high enough to keep the enzyme systems involved in ethanol oxidation saturated during the 60 min course of the experiment. The observation that the ethanol-induced decrease in plasma amino acid levels was more pronounced with higher ethanol doses indicates that not only the oxidation of ethanol but also ethanol itself is important in the effect of ethanol on plasma amino acid concentrations.     

Oxotremorine- and atropine-induced changes of dopamine metabolism in the rat striatum.

The effects of various doses of oxotremorine and of atropine (30 min, i.p.) on the metabolism of dopamine were examined in the striatum of the rat. Changes in striatal dopamine metabolism were estimated by following either the accumulation of [3H] dopamine 15 min after intravenous injection of [3H] tyrosine or the accumulation of dopa (taken as an index of dopamine synthesis) in animals pretreated with a dopa decarboxylase inhibitor Ro4-4602. Oxotremorine, 0-1 mg kg-1, and atropine, 1 mg kg-1, did not affect dopamine metabolism. Oxotremorine, 0-5 and 1-5 mg kg-1, did not modify dopamine concentrations but increased the accumulation of [3H]dopamine. The drug enhanced dopa formation in animals pretreated with Ro4-4602. Atropine, 5 and 20 mg kg-1, increased the accumulation of [3H]dopamine but did not affect dopamine concentrations. The accumulation of dopa was not modified there being no difference from the saline value in animals pretreated with the dopa decarboxylase inhibitor at high dopamine metabolism and atropine reduced dopamine utilization.     

Effect of 4-methylpyrazole on ethanol-induced decrease in rat plasma amino acids

It has been shown earlier that an acute dose of ethanol causes an immediate decrease in the concentration of most plasma amino acids, and that this decrease involves both beta-adrenergic and adrenocortical mechanisms. In this work is shown that the oxidation of ethanol also plays an important role in the amino acid decreasing effect. Male rats were pretreated with 4-methylpyrazole, an inhibitor of liver alcohol dehydrogenase, in doses causing an 85% inhibition of the ethanol elimination. In this group the ethanol-induced decrease in amino acids was much less pronounced than in a control group pretreated with saline.     

Ethanol-induced increase in brain concentrations of administered neutral amino acids

Summary Ethanol 2 g kg^–1 i.p. to rat increased the concentrations in the brain of administered large neutral amino acids (tyrosine, tryptophan, 5-hydroxytryptophan and -methyldopa). We have previously found a similar effect of ethanol on administered l-Dopa, resulting in increased brain/plasma ratios of dopa. Since large neutral amino acids are known to compete with each other for the carrier-mediated transport into the brain we suggest that the increased concentrations of the administered amino acids in the brain are at least partly the consequence of the ethanol-induced decrease in plasma amino acids observed previously.     

A dose-finding study on the effects of branch chain amino acids on surrogate markers of brain dopamine function

RATIONALE: We have previously shown in healthy volunteers that an amino acid mixture lacking tyrosine and phenylalanine reduces tyrosine availability to the brain and produces cognitive and neuroendocrine effects consistent with reduced dopamine function. This could provide a potential nutritional approach to disorders such as mania and schizophrenia, which are characterised by overactivity of dopamine pathways. The amino acid mixture we tested previously is unpalatable, whereas mixtures containing only branch chain amino acids can be made more palatable. However, the effects of such mixtures on dopamine function in humans have not been studied. OBJECTIVE: To assess the tolerability of different doses of branch chain amino acids and to measure their effects on neuroendocrine and cognitive measures sensitive to changes in dopamine function. METHODS: We used a randomised, double-blind, cross-over design in 12 healthy volunteers to assess the effect of single oral doses of 10 g, 30 g and 60 g branch chain amino acids on plasma prolactin and a test of spatial recognition memory RESULTS: The branch chain amino acids were well tolerated. The availability of tyrosine for brain catecholamine synthesis decreased in a dose-related manner. As hypothesised, the drink increased both the plasma prolactin and the latency to respond on the spatial recognition memory task. CONCLUSIONS: A drink containing branch chain amino acids is well tolerated in healthy volunteers and produces effects consistent with lowered dopamine function.     

Changes in brain tryptophan and tyrosine following acute and chronic morphine administration

Morphine increased brain concentrations of tryptophan and tyrosine 1–2 hr after administration in a dose-dependent manner in male rats. Concentrations of these amino acids in blood serum decreased 30–45 min post-injection and then rose towards control values. The rise in brain amino acids was antagonized by pretreatment with naloxone. In addicted rats there was only a slight increase in brain tryptophan and no increase in tyrosine. Thirty minutes after naloxone-precipitated withdrawal, tryptophan and tyrosine concentrations were elevated in brain, in contrast to the decline in these amino acids seen after naloxone administration in acutely morphinized rats.These results support the hypothesis that the elevated turnover of brain monoamines induced by morphine administration is related to increased availability of precursor amino acids in morphinized animals.     

Desensitization of the nicotine-induced mesolimbic dopamine responses during constant infusion with nicotine.

1. The effects of constant nicotine infusions (0.25, 1.0 and 4.0 mg kg-1 day-1) on extracellular dopamine levels in the nucleus accumbens (NAc) and on locomotor activity have been compared with the changes evoked by repeated daily injections (0.4 mg kg-1 day-1 for 5 days) of the drug. 2. The extracellular dopamine concentration in the NAc was significantly increased (P < 0.05) following a challenge dose of nicotine (0.4 mg kg-1, s.c.) in animals which had been pretreated with daily injections of the drug. This effect was accompanied by an enhanced locomotor response to nicotine. 3. The stimulant effects of nicotine on mesolimbic dopamine secretion and on locomotor activity were significantly inhibited (P < 0.01) by the prior administration of mecamylamine (2.0 mg kg-1, s.c.) but not by hexamethonium (2.0 mg kg-1, s.c.). 4. The constant infusion of nicotine at a rate of 1 and 4 but not 0.25 mg kg-1 day-1 abolished the sensitized dopamine response in the NAc to an injection of nicotine in animals pretreated with the drug. The locomotor responses to nicotine in the nicotine-pretreated rats were significantly attenuated by the infusion of nicotine at all 3 doses, although the nicotine induced locomotor activity, in the rats infused with 0.25 mg kg-1 day-1 was also significantly (P < 0.05) higher than that observed in the rats treated acutely with nicotine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dose and time effects of combined exposure to lead and ethanol on lead body burden and some neuronal, hepatic and haematopoietic biochemical indices in the rat

Ethanol (1, 2 or 5 g kg-1) and lead (0.55 g l-1 in drinking water) were given either alone or in combination for 4 months to rats. The uptake of lead in tissues, some lead-sensitive variables, the levels of biogenic amines in different brain regions, hepatic lipid peroxidation, glycogen and blood glucose concentrations were measured. Ethanol or lead when given alone inhibited the activity of blood delta-aminolevulinic acid dehydratase (ALAD). The co-administration of 5 g kg-1 but not 1 or 2 g kg-1 ethanol significantly enhanced the lead-induced inhibition of blood delta-ALAD activity and the elevation of delta-aminolevulinic acid (ALA) excretion. Co-exposure to lead and ethanol (5 g kg-1) produced a more pronounced increase in hepatic lipid peroxidation and blood glucose level than either ethanol or lead alone. This combination also caused a significant increase in the dopamine (DA) contents of striatum, midbrain and pons medulla, norepinephrine (NE) contents in midbrain and 5-hydroxytryptamine (5-HT) contents of hypothalamus, striatum, midbrain and pons medulla over levels produced by lead alone. However, the level of NE in hypothalamus decreased upon co-administration. The uptake and retention of lead was significantly higher in blood, liver, kidney and brain in animals co-exposed to lead and 5 g kg-1 ethanol. Blood and kidney lead was also increased by 2 g kg-1 ethanol. The results suggest that prolonged and heavy consumption of alcohol may increase the toxicity of lead.     

Aspartame fails to facilitate pentylenetetrazol-induced convulsions in CD-1 mice

Concentrations of plasma amino acids and brain monoamines as well as pentylenetetrazol-induced seizures were monitored in CD-1 mice treated with aspartame in acute oral doses from 0 to 2500 mg/kg. One hour after administration aspartame produced increases in plasma concentrations of phenylalanine and tyrosine and modest reductions in concentrations of brain serotonin and 5-hydroxyindole acetic acid. However, these effects of the sweetener had no influence on the convulsive dose fifty (CD50) of pentylenetetrazol. Moreover, aspartame failed to alter the percentage of mice exhibiting seizures when exposed to an approximate CD50 of pentylenetetrazol. Finally, aspartame had no effect on brain norepinephrine or dopamine concentrations. In sharp contrast to previously reported studies, these observations suggest that aspartame, given in heroic doses, does not alter the propensity to seizure activity in CD-1 mice. We conclude that changes in plasma amino acids and brain serotonin produced by large oral bolus doses of aspartame are insufficient to result in functional deficits which might have the capacity to facilitate pentylenetetrazol-induced seizures.     

Toluene-induced Decrease in Rat Plasma Concentrations of Tyrosine and Tryptophan

Abstract: The organic solvent toluene is demonstrated to cause a decrease in rat plasma concentrations of tyrosine and tryptophan both after intraperitoneal injections and after inhalation. Tyrosine and tryptophan are precursors to neurotransmitters and are transported from plasma into the brain. As the concentrations of these amino acids in plasma could influence the monoamine synthesis in the brain, this phenomenon might be of importance for the pathophysiology behind solvent-induced effects on brain function.     

Study of the ameliorating effects of an enteral nutrient for liver failure on hepatic encephalopathy: effects of SF-1008C on plasma and brain free amino acids, intracerebral amine concentrations and electroencephalogram in portacaval shunted rats with ammonia loading

The ameliorating effects of an enteral nutrient for liver failure (SF-1008C), which is enriched with branched-chain amino acids (BCAA) and includes few aromatic amino acids (AAA), were investigated. The blood ammonia, plasma and brain free amino acids, intracerebral amine concentrations and electroencephalogram were measured in portacaval shunted rats with 10% ammonium acetate (3 ml/kg, i.p.) (PCS) as a model of hepatic encephalopathy. The blood ammonia and plasma free amino acid concentrations in PCS rats were significantly increased in comparison to sham-operated (Sham) rats. Thus, the plasma BCAA/AAA ratio in PCS rats was appreciably reduced. Concomitant with the abnormal plasma amino acid concentrations, the brain free amino acid concentrations in PCS rats were markedly increased in comparison to the Sham rats. Moreover, the intracerebral tryptophan (Trp) and 5-hydroxyindol acetic acid (5-HIAA) concentrations were significantly increased, and the intracerebral dopamine (DA) concentration was significantly decreased in the PCS rats. The intracerebral serotonin (5-HT) and norepinephrine (NE) concentrations were, however, hardly changed. A smaller voltage for the electroencephalogram was used in the PCS rats than in the Sham rats. Abnormal plasma and brain free amino acid concentrations in PCS rats were normalized by oral administration of SF-1008C, and the low voltage electroencephalograms in the PCS rats were suppressed. On the other hand, abnormal plasma and brain free amino acid concentrations in the PCS rats were hardly normalized by oral administration of ED-AC, an elemental diet based on an amino acid composition of egg protein. These results suggest that SF-1008C affects brain free amino acids, intracerebral amine concentrations and electroencephalogram by ameliorating abnormal plasma free amino acid concentrations. Moreover, there is a highly significant correlation between the plasma BCAA/AAA ratio and the brain BCAA/AAA ratio, and this finding suggests that the plasma free amino acid patterns reflect the brain free amino acid patterns.     

Suppression by dopamine-agonists of the ethanol-induced stimulation of locomotor activity and brain dopamine synthesis

Summary Ethanol, 2.2 g/kg was given intraperitoneally to mice, grouped 3 by 3, alone or together with either of the dopamine-receptor stimulating agents apomorphine, 2.5 mg/kg, or ET 495, 5 mg/kg. Control animals received saline injections. Locomotor activity was then recorded every 5 min for 60 min, starting 5–7 min after the injection. Apomorphine and ET 495, which had no marked effect on the locomotor activity, both inhibited the locomotor stimulation induced by ethanol. Other animals received ethanol, 4 g/kg, alone or together with either apomorphine or ET 495, and at various time intervals thereafter, ³H-labelled tyrosine. Control animals received ³H-tyrosine alone. The net yield of ³H-dopamine and ³H-noradrenaline in the brain as well as the specific activity of ³H-tyrosine in plasma 10 min after the ³H-tyrosine injection were measured. Apomorphine and ET 495, 2.5 and 5 mg/kg, respectively, did not change the net yield of ³H-dopamine and ³H-noradrenaline. However, both of them inhibited the ethanol-induced increase in net yield of ³H-dopamine. This effect of apomorphine and ET 495 could not be ascribed to changes in the specific activity of ³H-tyrosine in the plasma. Apomorphine had no effect on the blood level of ethanol as measured 1 h after the administration of ethanol. The possibility that the inhibitory effects of the dopamine-agonists on the ethanol-induced stimulation of the dopamine synthesis and locomotor activity may be mediated by stimulation of presynaptic, inhibitory receptors is discussed.     

Effects of chronic nicotine pretreatment on (+)-amphetamine and nicotine-induced synthesis and release of [3H]dopamine from [3H]tyrosine in rat nucleus accumbens

The effects of chronic (14 day) administration of nicotine (1.5 mg kg-1 day-1) on the rat nucleus accumbens have been examined. Pretreatment of animals with nicotine increased the endogenous level of dopamine. The ability of (+)-amphetamine to stimulate formation and release of [3H]dopamine from [3H]tyrosine was greatly potentiated in tissue slices from the nucleus accumbens of rats pretreated with nicotine. Furthermore, nicotine was effective in stimulating the formation and release of from [3H]dopamine from [3H]tyrosine in tissue slices from chronic nicotine-treated animals.     

Effects of the beta 2-adrenoceptor agonist clenbuterol on tyrosine and tryptophan in plasma and brain of the rat

The beta 2-adrenoceptor agonist, clenbuterol (initially 5 mg/kg), was found to significantly reduce plasma tyrosine and raise brain tryptophan levels (P less than 0.01). By comparison, decreases in plasma tryptophan and increases in brain tyrosine were small and often nonsignificant. Amino acid levels measured in different brain regions revealed that the elevations were similar among the cerebellum, striatum, and cortex. These effects were partially blocked by propanolol but not by atenolol. The ED50 was estimated from dose-response curves to be about 0.05 mg/kg for both the decrease in plasma tyrosine and the increase in brain tryptophan. The effects of low doses of clenbuterol were prevented completely by propranolol. Peripheral organs displayed strikingly different patterns of change in amino acid concentrations. Only the spleen had any accumulation of tryptophan, but that was much less than in brain. In contrast, tyrosine and tryptophan were decreased in heart and unaltered in liver; tyrosine was decreased in lung. The elevation in brain tryptophan levels was attenuated by the beta 2-antagonist, ICI 118,551, but not by the beta 1-antagonist, betaxolol; but the reduction in plasma tyrosine was unaffected by either drug. The serotonin antagonist, methysergide, failed to block the effects of clenbuterol. We conclude that changes in amino acid concentrations produced by clenbuterol are mediated by beta 2-adrenoceptor stimulation. Although the increases in brain tyrosine and tryptophan were similar to increases in the plasma ratios of these amino acids to the sum of the other large neutral amino acids competing for transport into the brain, the disparity between the effects of ICI 118,551 in brain and plasma suggests that clenbuterol may also have a direct action in brain to regulate levels of aromatic amino acids. Since clenbuterol has been purported to have an antidepressant effect and since other antidepressants also increase brain tryptophan, this may be a common feature of antidepressant drug action.     

Effects of pentobarbital and diazepam on rat plasma amino acid patterns

Summary Intraperitoneal injections with pentobarbital and diazepam caused an increase in the concentration of most plasma amino acids in rat. In contrast, tryptophan was significantly decreased after treatment with pentobarbital. The tyrosine level showed no change and was thus actually reduced after pentobarbital treatment in relation to the total pool of large neutral amino acids. The possibility should be considered that these changes in plasma amino acid patterns may lead to reduced transport of e.g. tryptophan and tyrosine into the brain, which in turn might retard the synthesis of monoaminergic neurotransmitters. The transport and action of several aromatic amino acids used as therapetic agents may also be influenced.     

Beta-adrenergic regulation of amine precursor amino acid transport across the blood-brain barrier.

Beta-Adrenoceptor agonists were administered i.p. into rats and amino acid levels in brain and plasma were then determined to assess the effects on transport across the blood-brain barrier. Isoproterenol (10 mumol/kg) caused significant increases in aromatic amino acid (tyrosine, phenylalanine and tryptophan) levels in cerebral cortex and decreases in almost all amino acid concentrations in plasma. This effect of isoproterenol on brain tyrosine level was dose-dependent with an ED50 of 0.25 mumol/kg. Salbutamol (beta 2-adrenoceptor agonist, 10 mumol/kg) showed similar effects, but dobutamine (beta 1-adrenoceptor agonist, 50 mumol/kg) failed to increase brain amino acid levels. When 1-threo-3,4-dihydroxyphenylalanine (L-DOPA, 100 mumol/kg) was i.p. loaded, beta-adrenoceptor agonists promoted the transport of L-DOPA into brain without increasing the clearance rate of plasma L-DOPA. Moreover, significant increases in dopamine and its metabolites were observed in rat brain. These findings suggest that the transport of aromatic amino acids across the blood-brain barrier may be regulated through beta 2-adrenoceptors and that co-administration of beta 2-adrenoceptor agonists with L-DOPA may enhance the therapeutic efficacy of L-DOPA.     

Very low doses of ethanol induce behavioral changes involving dopamine D2 receptors

In male rats, pretreatment for 20 days with very low (0.5, 1%, v/v) but not with high (5, 10%, v/v) oral doses of ethanol delayed the initiation and reduced the duration of narcosis induced by an acute high intraperitoneal (i.p.) dose of the drug (3 g/kg in 25% saline solution). Furthermore, the treatment improved the acquisition of shuttle-box active avoidance response but did not affect the emission of ultrasonic calls, an index of emotional state of animals. These effects were inhibited by peripheral administration of the dopamine D2 receptor antagonist, sulpiride (1 mg/kg). A higher dose of sulpiride (10 mg/kg) prolonged the duration of narcosis in rats pretreated with high-dose ethanol and reduced the number of conditioned avoidance responses in the shuttle-box paradigm. The pretreatment with the dopamine D2 receptor agonist, (+/-)-2-(N-phenethyl-N-propylamino)-5-hydroxytetralin (PPHT, 0.1 mg/kg), enhanced the effects of ethanol very low doses in delaying the initiation and reducing the duration of narcosis induced by an acute i.p. dose of the drug. A pharmacokinetic study in ethanol-pretreated animals revealed that administration of 0.5% or 1% ethanol for 20 days did not modify significantly the bioavailability of acute ethanol administered i.p. in a dose of 3 g/kg in 25% saline solution. Thus, repeated administration of ethanol very low doses may have affected the sensitivity of presynaptic dopamine D2 receptors. The influence on dopamine release through an action on presynaptic receptors may be involved in these effects of small doses of ethanol.     

Free tryptophan/large neutral amino acids ratios in blood plasma do not predict cerebral spinal fluid tryptophan concentrations in interleukin-1-induced anorexia

Peripheral administration of interleukin-1 (IL-1) reduces food intake and affects brain serotonergic activity, suggesting a causal relationship. Furthermore, IL-1 increases the brain concentrations of the serotonin precursor, tryptophan (TRP), by unclear mechanism(s). We aimed at confirming the link between IL-1 administration, raised brain TRP concentrations and the development of anorexia, and at investigating the mechanisms of TRP entry into the brain. Thirty adult, overnight fasted Sprague-Dawley rats were randomly assigned to i.p. injections of 1 mug/kg BW of IL-1 alpha (n=10) or vehicle (n=10), or to pair-feeding with IL-1 animals (n=10). After 2 h, food intake, blood plasma concentrations of total TRP, free TRP, large neutral amino acids (LNAA; competing with TRP for brain entry) were measured. Cerebral spinal fluid (CSF) TRP concentrations were also measured. TRP brain availability was assessed by calculating the plasma ratio free TRP/LNAA. Following IL-1 injection, food intake significantly declined in IL-1 rats, which was paralleled by decreased plasma free TRP and increased plasma LNAA. Despite a decrease in the free TRP/LNAA ratios in plasma, IL-1 significantly increased concentrations of TRP in CSF. These data show that the acute peripheral administration of IL-1 induces anorexia and raises CSF TRP levels. Considering the possible role of the raised CSF TRP in influencing brain serotonin activity, it is postulated that increased serotonergic neurotransmission could be involved in IL-1 induced anorexia.     

Effects of rapid depletion of phenylalanine and tyrosine on sleep and behavior

The effects of fluctuations of free amino acid concentrations in plasma on sleep patterns and operant behavior in the squirrel monkey were studied. Plasma phenylalanine (PHE) and tyrosine (TYR) were rapidly lowered to trace levels within 4 hr by intraperitoneal administration of phenylalanine ammonia-lyase (PAL), an enzyme which specifically deaminates both PHE and TYR to inactive products. Significant alterations in sleep patterns and in performance on a chained operant task involving hold and reaction time components were found, but no significant effect on the performance of a simple operant task was observed. Administration of saline or trans-p-cinnamic acid and trans-p-coumaric acid, the products of PHE and TYR deamination, produced no changes in behavior or sleep patterns. The reduction of plasma PHE and TYR resulted in a significant decrease in PHE and TYR levels in whole rat brain. Brain serotonin levels were increased within 4 hr after PAL administration, whereas, dopamine and norepinephrine levels were decreased subsequently (within 8 hr). These studies suggest that circulating levels of PHE and TYR are involved directly or indirectly in the modulation of certain parameters of brain function.     

Acute effects of ethanol and acetaldehyde on plasma phosphate level

Oral administration of ethanol in a dose of 65 mmol kg-1 produced marked change of plasma phosphate level in rabbits. Hypophosphataemia was observed for the first 2 h after administration followed by significant increase of plasma phosphate at 5 h. Hypophosphataemia did not appear when ethanol was given to the rabbits pretreated with pyrazole. When animals were injected with disulfiram in advance, the duration of hyperphosphataemia due to ethanol was prolonged. Administration of acetaldehyde at a dose of 1.5 mmol kg-1 produced hyperphosphataemia. In this study, plasma phosphate was not associated with change in calcium level. These results suggest that the hypophosphataemia observed was related to the metabolic process of ethanol utilizing alcohol dehydrogenase, and that acetaldehyde, a metabolite of ethanol, might induce the hyperphosphataemia in the animals.