Increased dietary protein elevates plasma uric acid and is associated with decreased oxidative stress in rapidly-growing broilers

Uric acid is an important antioxidant and methods to elevate its plasma concentration may be important in animal health. In a first study, the effect of dietary protein on plasma uric acid (PUA) and glucose concentrations were determined in 3-week-old chicks. Twenty-four broiler chicks were randomly assigned to four diets: a commercial control diet (C, 20% crude protein), low protein (LP) containing 10% casein, medium protein (MP) containing 20% casein or high protein (HP) containing 45% casein for a 3-week experiment. PUA concentration increased (P<0.05) in chicks fed HP diet and declined (P<0.05) in chicks fed LP while plasma glucose concentrations were lower (P<0.05) in chicks fed the LP diet at the end of the study. In a second study, PUA and leukocyte oxidative activity (LOA) were determined in broilers fed C, LP, MP or HP diets for 4 weeks. As in the first study, dietary protein directly affected PUA concentrations. In birds consuming HP diets, PUA was negatively correlated (P=0.06) with lowered LOA. These data support the view that increases in dietary protein can increase PUA concentrations, which can ameliorate oxidative stress.     

The Significance of Homovanillic Acid and 3,4-Dihydroxyphenylacetic Acid Concentrations in Human Lumbar Cerebrospinal Fluid

The concentrations of the acidic dopamine (DA) catabolites homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) measured in human CSF are supposed to reflect the "turnover" of DA in the brain. The notion of "turnover" is, however, not synonymous with impulse nerve activity in the dopaminergic systems. Significant amounts of DOPAC and HVA could, indeed, be demonstrated in brain structures wherein dopaminergic innervation has not been documented. It must also be noted that DA is not only a neurotransmitter itself, but also a precursor of norepinephrine and epinephrine. Furthermore, in lumbar CSF, levels of biogenic amine catabolites partially reflect metabolism in the spinal cord and may have limited relevance to neurotransmission in the brain. To elucidate these points further, we determined the concentrations of DOPAC and HVA in 22 areas of six human brains and eight levels of six human spinal cords. The data were correlated with the concentration of DA. Quantitative determinations were done using HPLC with electrochemical detection, after solvent and ion-pair extraction. In this study, significant amounts of both DOPAC and HVA were demonstrated in brain structures not previously associated with dopaminergic innervation. The relatively lower DA concentration in these structures suggests that in these regions, the DOPAC and HVA concentrations are unrelated to dopaminergic neurotransmission. The possible role of capillary walls and glial cells in the catabolism of DA must be further evaluated. The demonstration of DOPAC and HVA in the spinal cord is another argument against the hypothesis that CSF levels of HVA and DOPAC reflect closely the activity of the dopaminergic systems in the brain.     

Rhythmic changes in metabolism of dopamine in the chick retina: the importance of light versus biological clock

Rhythmic changes in dopamine (DA) content and metabolism were studied in retinas of chicks that were adapted to three different lighting conditions: 12-h light : 12-h dark (LD), constant darkness (DD) and continuous light (LL). Retinas of chicks kept under LD conditions exhibited light-dark-dependent variations in the steady-state level of DA and the two metabolites of DA, i.e. 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA). Concentrations of DA, DOPAC and HVA were high in light hours and low in dark hours of the LD illumination cycle. In retinas of chicks kept under DD, the content of DA, DOPAC and HVA oscillated in a rhythmic manner for 2 days, with higher values during the subjective light phase than during the subjective dark phase. The amplitudes of the observed oscillations markedly and progressively declined compared with the amplitudes recorded under the LD cycle. In retinas of chicks kept under LL conditions, levels of DA, DOPAC and HVA were similar to those found during the light phase of the LD cycle. Changes in the retinal contents of DA and HVA did not exhibit pronounced daily oscillations, while on the first day of LL the retinal concentrations of DOPAC were significantly higher during the subjective light phase than during the subjective dark phase. Acute exposure of chicks to light during the dark phase of the LD cycle markedly increased DA and DOPAC content in the retina. In contrast, light deprivation during the day decreased the retinal concentrations of DA and DOPAC. It is suggested that of the two regulatory factors controlling the level and metabolism of DA in the retina of chick, i.e. light and biological clock, environmental lighting conditions seem to be of major importance, with light conveying a stimulatory signal for the retinal dopaminergic cells.     

Kinetics of Drug-Induced Changes in Dopamine and Serotonin Metabolite Concentrations in the CSF of the Rat

Cerebrospinal fluid (CSF) was removed at a constant flow rate of 1 microliter/min from the third ventricle of anesthetized rats. Every 15 min, CSF dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were determined by direct injection of CSF into a liquid chromatographic system coupled with electrochemical detection. Mean CSF concentrations of DOPAC, HVA, and 5-HIAA were 1.29 microM, 0.88 microM, and 2.00 microM, respectively. In order to determine the turnover rates of dopamine (DA) and serotonin, experiments using monoamine oxidase (MAO) inhibition were performed. Tranylcypromine (20 mg/kg i.p.) induced a sharp exponential decrease of CSF DOPAC, HVA, and 5-HIAA, with respective half-lives of 15.60 min, 16.91 min, and 77.23 min. Their respective turnover rates were 3.74, 2.22, and 1.18 nmol X ml-1 X h-1. m-Hydroxybenzylhydrazine (NSD-1015, 100 mg/kg i.p.) and monofluoromethyl-DOPA (100 mg/kg i.p.), two decarboxylase inhibitors, induced a slow exponential decrease of all three CSF metabolites. alpha-Methyl-p-tyrosine (250 mg/kg i.p.) also induced a slow exponential decrease of DOPAC and HVA. These decreases of CSF DOPAC and HVA induced by DA synthesis inhibitors may reflect the turnover of DA in vivo. Haloperidol (0.5 mg/kg i.p.) considerably enhanced CSF DOPAC and HVA without affecting 5-HIAA, confirming that dopaminergic receptors modulate DA neurotransmission in vivo. Haloperidol administered 1.5 h after NSD-1015 did not increase DOPAC and HVA, in contrast to reserpine (5 mg/kg i.p.) injected under the same conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative analysis of indices of central dopaminergic functions in man

Various postulated indices of central dopaminergic activity - cerebrospinal fluid (CSF) dopamine (DA), dihydroxy-phenylacetic acid (DOPAC), homovanillic acid (HVA), noradrenaline (NA), plasma NA, serum prolactin, serum dopamine-β-hydroxylase (DBH), and platelet monoamine oxidase (MAO) activity - were measured in 30 drug-free inpatients. The mean values and the ranges were similar to those described in the literature. Plasma NA showed significant positive correlation with age. Significant positive correlation was found between CSF DA and its metabolites DOPAC and HVA. Serum DBH activity showed a slight but significant inverse correlation with CSF DA and its two metabolites. CSF NA showed a significant positive correlation with CSF DOPAC, but only in females. Serum DBH activity had no significant correlation either with CSF or with plasma NA levels. These findings suggest that either CSF HVA or DOPAC and DA may be useful indicators of DA metabolism in humans. Serum DBH activity may be in relationship with the central dopaminergic functions.     

Increased Cerebrospinal Fluid Dopamine and 3,4-Dihydroxyphenylacetic Acid Levels in Huntington''s Disease: Evidence for an Overactive Dopaminergic Brain Transmission

Levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), noradrenaline (NA), 3-methoxy-4-hydroxyphenylglycol (MHPG), and 5-hydroxyindoleacetic acid (5-HIAA) in the CSF of patients with Huntington's disease (HD) were measured by HPLC. CSF DA, DOPAC, and MHPG levels were found to be increased in HD patients. Levels of HVA, 5-HIAA, and NA in the CSF of HD patients did not differ from those of controls. Changes in CSF DA and DOPAC levels were consistent with previous findings of increased DA tissue content in some brain areas of patients with HD. These results suggest that CSF DOPAC levels could be a more reliable index of overactive dopaminergic brain systems in HD than CSF HVA levels.     

谷氨酸和MK-801对正常和帕金森模型大鼠纹状体内多巴胺代谢的影响

采用微透析和高效液相色谱一电化学(HPLC-ECD)技术研究了谷氨酸和MK-801对正常和帕金森模型人鼠纹状体内多巴胺代谢的影响。用微透析技术在大鼠纹状体内分别定位给以左旋多巴、L-谷氨酸和／或MK-801,同时收集透析液,用HPLC-ECD方法测定透析液中多巴胺代谢产物的浓度。微透析和HPL-ECD分析结果表明：纹状体内定位给以序旋多巴,正常大鼠和帕金森模型大鼠纹状体内多巴胺代谢产物的浓度均升高;纹状体内定位给以L-谷氨酸,可使正常大鼠纹状体内多巴胺代谢产物的浓度降低,但对帕金森火鼠模型纹状体内多巴胺代谢产物浓度的降低不显著;纹状体内定位给以MK-801,正常人鼠纹状体内多巴胺代谢产物的浓度升高：但对帕金森人鼠模型纹状体内多巴胺代谢产物浓度的升高不显著：纹状体内同时定位给以MK-80l和L-谷氨酸,可以有效防止L-谷氨酸所致正常人鼠纹状体内多巴胺代谢产物浓度的降低。结果提示,谷氦酸可以通过NMDA受体调节多巴胺的代谢。尽管非竞争性NMDA拈抗剂MK-801可以有效防止L-谷氨酸所敛正常人鼠纹状体内多巴胺代谢产物浓度的降低,但却不能有效地改善帕金森大鼠模型纹状体内多巴胺的代谢水平。因此存正常及帕金森病情况下,谷氮酸一多巴胺相互作用机制和MK-801改善帕金森病的机制还有待进一步研究。     

Linoleic acid derived oxylipins are elevated in kidney and liver and reduced in serum in rats given a high-protein diet

High protein (HP) diets are often used as a means to reduce obesity, but their long-term effects remain unclear. In vitro studies suggest the involvement of a subset of oxylipins in the tissue response to HP diets. To examine the role of these bioactive lipids in vivo, normal adult male Sprague Dawley rats were provided isocaloric diets with LP (low protein, 8% protein by weight), NP (normal protein, 14%) or HP (50%) diets for 2 weeks, and targeted lipidomic analysis of oxylipins in kidney (cortex and medulla), liver and serum was performed by HPLC-MS/MS. The main group of oxylipins affected by the HP diet was the oxylipins derived from linoleic acid (LA), many of which were elevated in kidney (particularly the medulla) and liver, but reduced in serum of rats provided the HP compared to NP or LP diets. A smaller proportion of other n-6 fatty acid derived oxylipins were lower in kidney and higher in liver, and none were affected in serum, by HP feeding. Few n-3 oxylipins were affected by protein level. In liver only, the oxylipin product to substrate ratios of the soluble epoxide hydrolase enzyme were higher in LP fed rats. Differences between cortex and medulla oxylipins suggest relatively higher cortex activity of 5- and 8-lipoxygenase and cytochrome P450 hydroxylase, and higher medulla cyclooxygenase and 12- and 15-lipoxygenase activity. Further studies are needed to elucidate the physiological effects of the changes in these novel oxylipins in response to short-term dietary HP.     

The level of dietary protein and carbohydrate has a different effect on intestinal uptake of hexoses and lipids in rabbits with an ileal resection than in those with an intact intestinal tract

Either high protein, low carbohydrate (HP) or low protein, high carbohydrate (LP) diets were fed for 6 weeks to rabbits with or without resection of the distal half of the small intestine. Control and resected rabbits fed HP consumed more food and gained more weight than the animals fed LP. The level of dietary protein has a different effect on intestinal transport in animals with an ileal resection than in those with an intact small intestine. With 0.5 mM glucose, the in vitro uptake in control rabbits was greater for the LP than HP diet but was unchanged in resected rabbits; uptake of 0.5 mM galactose and 3-O-methyl glucose was unaffected by HP and LP, whereas in rabbit uptake was lower in LP than HP. The uptake of 40 mM glucose was greater with the LP than HP diet in control rabbits, but lower with LP than HP in resected rabbits. In control rabbits, the uptake of aluric acid was lower on the LP than HP diet; the uptake of octanoic acid, decanoic acid, and cholesterol was unchanged; and the uptake of each fatty acid and cholesterol was greater in resected rabbits fed LP than HP. Feeding a low protein diet to animals with an ileal resection is associated with lower jejunal uptake of high concentrations of glucose, but the higher uptake of galactose and enhanced permeability to fatty acids result in superior weight gain. Thus, recommendations for alterations in dietary protein and carbohydrate levels following ileal resection must be made with the knowledge that these changes may influence intestinal transport function as well as body weight gain.     

The effect of dietary precursors on the excretion of amines and their metabolites in the rat

The influence of diet on the excretion of catecholamines, some of their metabolites, and pHPG, an octopamine metabolite, was examined. Two groups of rats were fed either a cereal-containing standard laboratory Purina rat chow or a cereal-free casein diet. Use of the standard chow resulted in significant increases in the urinary values for total MHPG, pHPG, DHPE, MHPE, and free and total DOPAC by the seventh day in comparison to the casein diet. No changes were noted in the excretion of free and total NE, DA, and HVA. The data indicate that it is necessary to place the animals on the casein diet several days before determining the excretion of the aforementioned metabolites.     

The influence of substance P central administration on ethanol intake in rats chronically exposed to alcohol

The influence of central substance P (SP) administration on alcohol intake and brain dopamine metabolism within mesocortico-limbic and nigrostiatal systems of rats exposed to ethanol, was studied. During 6 months, the rats consumed 15% ethanol solution instead of water. Central administration of SP (3 mcg/kg) decreased alcohol consumption by 41% in alcohol-preference animals. After long-term ethanol exposure ratios DOPAC/DA and HVA/DA were reduced in striatum and accumbens. SP in dose 3 mcg/kg increased content of DOPAC by 17% and HVA by 23% as well as DOPAC/DA by 9%, HVA/DA by 19% in accumbens. Whereas in striatum only increased DOPAC (28%) and HVA (29%) were observed as compared with saline-treated rats.     

Intracerebral dialysis: direct evidence for the utility of 3-MT measurements as an index of dopamine release

Intracerebral dialysis was used to monitor the in vivo efflux of striatal dopamine (DA), homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC) and 3-methoxytyramine (3-MT) in the pentobarbital anesthetized rat. In untreated rats, there were low levels of extra-cellular DA and 3-MT which were increased 15-fold by treatment with amphetamine. Under basal and drug-stimulated conditions, 3-MT concentrations were maintained at approximately 30% of the extracellular DA levels. These data agree with in vivo turnover estimates which indicate that 20 to 30% of DA turnover is through the 3-MT pool in the striatum. In contrast, extracellular DOPAC and HVA levels were reduced only slightly by amphetamine and with a delayed onset. Our data support the hypothesis that striatal DOPAC is an accurate index of intraneuronal DA metabolism and that 3-MT is an index of the extracellular concentration of DA.     

Changes in catecholamines and dopaminergic metabolites in pigeon brain during development from the late embryonic stage toward hatch

While brain development during embryogenesis has been extensively studied in precocial birds, there is no information available on altricial birds. Thus, the concentrations of the catecholamines norepinephrine (NE), epinephrine (E), and dopamine (DA), and the dopaminergic metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and 4-hydroxy-3-methoxyphenylacetic acid (HVA) were determined at several stages during the late embryonic period (E13, E14, E15, E16, E17 and E18) and the day-of-hatch (P0) in the pigeon telencephalon, cerebellum, optic lobe, and brainstem. The concentrations of all catecholamines were higher than those reported in chicken embryos. During embryogenesis, NE, E, DOPAC and HVA concentrations in the various brain parts increased throughout embryonic development until shortly before hatching at which time they decreased. DA, however, continued to increase through hatching in the brainstem, and the changes in DA concentrations varied in several brain parts. In conclusion, catecholamine concentrations in the various brain parts tended to increase with embryonic age, and the concentrations were higher than those in chickens. Furthermore, brain catcholamine metabolism changed at hatch in pigeons.     

Effect of chloral hydrate on in vivo KCl-induced striatal dopamine release in the rat

The release of striatal dopamine (DA) and its metabolites in response to locally-induced K⁺ depolarization was investigated in vivo in chloral hydrate-anesthetized and freely moving rats. KCl at concentrations of 30, 50, and 100 mM induced significant dose-dependent increases in extracellular DA overflow in both chloral hydrate-anesthetized and freely moving rats (P<0.05). Extracellular levels of dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were decreased. The DA overflow in response to 30 mM KCl stimulation in anesthetized rats was significantly greater than that in freely moving rats (P<0.05). In addition, chloral hydrate anesthesia resulted in a significant decrease in extracellular levels of DOPAC and significant increases in extracellular levels of HVA and 5-HIAA in comparison with freely moving rats (P<0.05). Furthermore, the basal level of extracellular HVA in chloral hydrateanesthetized rats was significantly higher than that in freely moving rats. These results suggest that chloral hydrate anesthesia could have significant effects on the pharmacological response of the striatal dopaminergic neurons.     

Formation and Metabolism of Dopamine in Nine Areas of the Rat Brain: Modifications by Haloperidol

The rate of removal of 3,4-dihydroxyphenylacetic acid (DOPAC) in nine rat brain areas (striatum, nucleus accumbens, tuberculum olfactorium, hypothalamus, lateral hippocampus, occipital cortex, brain stem, cerebellum, and retina) was calculated from its exponential decline after monoamine oxidase inhibition by pargyline. The experiments were carried out with rats pretreated with either saline or haloperidol. It appeared that the efficiency with which DOPAC was removed from the brain (expressed by the fractional rate constant k) varied considerably throughout the brain. Haloperidol dramatically decreased the k values, and in addition these effects differed widely in the various brain areas. Similarly to DOPAC, haloperidol had a pronounced retarding effect on the efflux of homovanillic acid (HVA) from the brain. These findings strongly suggest that great care should be taken when drug-induced alterations in DOPAC and HVA concentrations are interpreted as changes in dopaminergic activity. The dopamine (DA) concentrations were measured in the same experiments, but it appeared that the pargyline-induced rise in DA was of limited use for the estimation of the synthesis rate of the amine. We calculated the rate of catecholamine synthesis in the nine brain areas from the rise of 3,4-dihydroxyphenylalanine (DOPA) during decarboxylase inhibition. In saline- as well as in haloperidol-pretreated rats it was found that the total catecholamine synthesis rate in the typical dopaminergic areas (striatum, nucleus accumbens, and tuberculum olfactorium) was of the same order of magnitude as the DOPAC rate of removal. This confirms that DOPAC formation is quantitatively the main route of degradation in these brain areas.(ABSTRACT TRUNCATED AT 250 WORDS)     

Supplementation with branched-chain amino acids to a low-protein diet regulates intestinal expression of amino acid and peptide transporters in weanling pigs

This study determined the effects of dietary branched-chain amino acids (AA) (BCAA) on growth performance, expression of jejunal AA and peptide transporters, and the colonic microflora of weanling piglets fed a low-protein (LP) diet. One hundred and eight Large White × Landrace × Duroc piglets (weaned at 28 days of age) were fed a normal protein diet (NP, 20.9 % crude protein), an LP diet (LP, 17.1 % crude protein), or an LP diet supplemented with BCAA (LP + BCAA, 17.9 % crude protein) for 14 days. Dietary protein restriction reduced piglet growth performance and small-intestinal villous height, which were restored by BCAA supplementation to the LP diet to values for the NP diet. Serum concentrations of BCAA were reduced in piglets fed the LP diet while those in piglets fed the LP + BCAA diet were similar to values for the NP group. mRNA levels for Na⁺-neutral AA exchanger-2, cationic AA transporter-1, b^0,+ AA transporter, and 4F2 heavy chain were more abundant in piglets fed the LP + BCAA diet than the LP diet. However, mRNA and protein levels for peptide transporter-1 were lower in piglets fed the LP + BCAA diet as compared to the LP diet. The colonic microflora did not differ among the three groups of pigs. In conclusion, growth performance, intestinal development, and intestinal expression of AA transporters in weanling piglets are enhanced by BCAA supplementation to LP diets. Our findings provide a new molecular basis for further understanding of BCAA as functional AA in animal nutrition.     

Liver Nonprotein Sulfhydryl and Taurine Concentrations,and Fat Content of Rats Fed a Low Protein Diet Supplemented with Sulfur-containing Amino Acids

The relative excess of some catabolites of sulfur-containing amino acids in the liver of rats fed a low protein diet might be one of the factors which cause the liver fat accumulation. To investigate the possibility were studied relationships between changes in concentrations of some metabolites of sulfur-containing amino acids and those in fat contents of rats fed a low protein diet consisting of heated soybean flour, casein or wheat flour with or without added methionine, threonine or lysine. The addition of 0.6% methionine to the 25% heated soybean flour diet increased the nonprotein-sulfhydryl (NP–SH) concentration and fat content in the liver. These changes were prevented by the further addition of 0.5% threonine to the diet, although the NP–SH concentration was remarkably higher than that of rats fed the unsupplemented diet. The addition of 0.6% cystine HC1 to the 25% heated soybean flour diet containing sufficient choline elevated the NP–SH concentration and fat content in the liver, which were not affected by the further addition of 0.5% threonine. The addition of 0.6% cystine HC1 to the 10% casein diet significantly increased the fat content, and NP–SH and taurine concentrations in the liver. The further addition of 0.5 % threonine completely decreased the fat content, and partially reduced the NP–SH and taurine concentrations. Effects of supplementation of 0.4% lysine HC1 to the 70% wheat flour diet on the fat content and NP–SH concentration in the liver demonstrated the trends similar to those of supplementation of cystine to the 10% casein diet. The further addition of threonine remarkably decreased the fat content, NP–SH and taurine concentrations in the liver.     

Determination of Picomole Amounts of Dopamine, Noradrenaline, 3,4-Dihydroxyphenylalanine, 3,4-Dihydroxyphenylacetic Acid, Homovanillic Acid, and 5-Hydroxyindolacetic Acid in Nervous Tissue After One-Step Purification on Sephadex G-10, Using High-Performance Liquid Chromatography with a Novel Type of Electrochemical Detection

A determination of dopamine (DA), noradrenaline (NA), 3,4-dihydroxyphenylalanine (DOPA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindolacetic acid (5-HIAA) in nervous tissue is described. The method is based on a rapidly performed isolation of DA, NA, DOPA, DOPAC, HVA, and 5-HIAA from one single nervous tissue sample on small columns of Sephadex G-10, followed by reverse-phase high-performance liquid chromatography with electrochemical detection. A new type of electrochemical detector based on a rotating disk electrode (RDE) was used. The rotating disc electrode was found to be a reliable and sensitive amperometric detector with several advantages over the currently used thin-layer cells. The detector appeared very useful for routine analysis. Practical details are given for the routine use of the RDE. Brain samples containing no more than 75-150 pg (DA, DOPA, DOPAC, HVA, and 5-HIAA) or 500 pg (NA) could be reproducibly assayed with high recovery (approx. 85%) and precision (approx. 5%), without the use of internal standards. Endogenous concentrations of DA, NA, DOPA, DOPAC, HVA, and 5-HIAA were determined in eight brain structures.     

Human prostaglandin H synthase (hPHS)-1- and hPHS-2-dependent bioactivation, oxidative macromolecular damage, and cytotoxicity of dopamine, its precursor, and its metabolites

The dopamine (DA) precursor l-dihydroxyphenylalanine (L-DOPA) and metabolites dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 3-methoxytyramine may serve as substrates for prostaglandin H synthase (PHS)-catalyzed bioactivation to free radical intermediates. We used CHO-K1 cells expressing human (h) PHS-1 or hPHS-2 to investigate hPHS isozyme-dependent oxidative damage and cytotoxicity. hPHS-1- and hPHS-2-expressing cells incubated with DA, L-DOPA, DOPAC, or HVA exhibited increased cytotoxicity compared to untransfected cells, and cytotoxicity was increased further by exogenous arachidonic acid (AA), which increased hPHS activity. Preincubation with catalase, which detoxifies reactive oxygen species, or acetylsalicylic acid, an inhibitor of hPHS-1 and -2, reduced the cytotoxicity caused by DA, L-DOPA, DOPAC, and HVA in hPHS-1 and -2 cells both with and without AA. Protein oxidation was increased in hPHS-1 and -2 cells exposed to DA or L-DOPA and further increased by AA addition. DNA oxidation was enhanced earlier and at lower substrate concentrations than protein oxidation in both hPHS-1 and -2 cells by DA, L-DOPA, DOPAC, and HVA and further enhanced by AA addition. hPHS-2 cells seemed more susceptible than hPHS-1 cells, whereas untransfected CHO-K1 cells were less susceptible. Thus, isozyme-specific, hPHS-dependent oxidative damage and cytotoxicity caused by neurotransmitters, their precursors, and their metabolites may contribute to neurodegeneration associated with aging.     

7-Nitroindazole enhances amphetamine-evoked dopamine release in rat striatum. an in vivo microdialysis and voltammetric study.

The intracellular second messenger nitric oxide (NO) is implicated in a variety of physiological functions, including release and uptake of dopamine (DA). In the described study, in vivo microdialysis and differential pulse voltammetric techniques were used to determine the involvement of NO in release of DA and its metabolites (dihydroxyphenylalanine, DOPAC; homovanillic acid, HVA) in neostriatum of freely moving rats. While the NO donor molsidomine (30.0 mg/kg; MOLS) and neuronal NO synthase- (nNOS-) inhbitor 7-nitroindazole (10.0 mg/kg; 7-NI) had no effect on the basal in vivo microdialysate level of DA, 7-NI specifically enhanced D,L-amphetamine-(1.0 mg/kg i.p.; AMPH) evoked release of DA. Basal or AMPH effects on DOPAC and HVA levels were not influenced by MOLS or 7-NI. Findings indicate that nitrergic systems have an important role in mediating effects of AMPH on dopaminergic systems.