Salsolinol, a tetrahydroisoquinoline-derived neurotoxin, induces oxidative modification of neurofilament-L protection by histidyl dipeptides

Salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline) is a compound derived from dopamine metabolism and is capable of causing dopaminergic neurodegeneration. Oxidative modification of neurofilament proteins has been implicated in the pathogenesis of neurodegenerative disorders. In this study, oxidative modification of neurofilament-L (NF-L) by salsolinol and the inhibitory effects of histidyl dipeptides on NF-L modification were investigated. When NF-L was incubated with 0.5 mM salsolinol, the aggregation of protein was increased in a time-dependent manner. We also found that the generation of hydroxyl radicals (?OH) was linear with respect to the concentrations of salsolinol as a function of incubation time. NF-L exposure to salsolinol produced losses of glutamate, lysine and proline residues. These results suggest that the aggregation of NF-L by salsolinol may be due to oxidative damage resulting from free radicals. Carnosine, histidyl dipeptide, is involved in many cellular defense processes, including free radical detoxification. Carnosine, and anserine were shown to significantly prevent salsolinol- mediated NF-L aggregation. Both compounds also inhibited the generation of ?OH induced by salsolinol. The results indicated that carnosine and related compounds may prevent salsolinol-mediated NF-L modification via free radical scavenging.     

Inhibition of Catechol-O-Methyltransferase by 6,7-Dihydroxy-3,4-Dihydroisoquinolines Related to Dopamine: Demonstration Using Liquid Chromatography and a Novel Substrate for O-Methylation

We report that 6,7-dihydroxy-3,4-dihydroisoquinolines related to dopamine are potent inhibitors of catechol-O-methyltransferase (COMT), but are not apparent substrates for the enzyme in vitro or in vivo. Three dihydroxy (catecholic) dihydroisoquinolines, including the 1-benzyl (DesDHP) and the 1-methyl (DSAL) analogs, were found to inhibit COMT activity in rat liver supernatant more effectively than the well-known inhibitor, tropolone. Inhibition of O-methylation was uncompetitive with substrate, and O-methylated products of the catecholic dihydroisoquinolines were undetectable. For these in vitro studies, a facile liquid chromatographic assay was developed utilizing as a site-specific substrate, 1-methyl-6,7-dihydroxy-tetrahydroisoquinoline-1-carboxylate (salsolinol-1-carboxylate). This catechol produces only one phenolic product isomer when incubated with liver supernatant and S-adenosylmethionine. Following central injection of DSAL in rats, inhibition of brain COMT in vivo was indicated by the reduced brain levels of homovanillic acid, but not of 3,4-dihydroxyphenylacetic acid. Furthermore, O-methylated DSAL metabolites could not be detected in brain by liquid or gas chromatography. We suggest that 6,7-dihydroxy-dihydroisoquinolines are "nonmethylatable" COMT inhibitors because they exist as quinoidal tautomers resembling pyridones or tropolones rather than as catechols. Quinoid formation is supported by the fluorescence and ultraviolet spectra for DSAL and its O-methyl derivatives. The experiments reveal a new class of COMT inhibitors that may be of pharmacological and mechanistic value. Additionally, 3,4-dihydroisoquinolines could arise endogenously via oxidation of the 1,2,3,4-tetrahydroisoquinolines which are ingested or produced from cellular catecholamine condensations. However, it is unlikely that dihydroisoquinoline (e.g., DSAL) concentrations necessary to inhibit COMT significantly would be attained via endogenous pathways.     

Salsolinol, a tetrahydroisoquinoline catechol neurotoxin, induces human Cu,Zn-superoxidie dismutase modificaiton

The endogenous neurotoxin, 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), has been considered a potential causative factor for the pathogenesis of Parkinsonos disease (PD). In the present study, we examined the pattern of human Cu,Zn-superoxide dismutase (SOD) modification elicited by salsolinol. When Cu,Zn-SOD was incubated with salsolinol, some protein fragmentation and some higher molecular weight aggregates were occurred. Salsolinol led to inactivation of Cu,Zn-SOD in a concentration-dependent manner. Free radical scavengers and catalase inhibited the salsolinolmediated Cu,Zn-SOD modificaiton. Exposure of Cu,Zn-SOD to salsolinol led also to the generation of protein carbonyl compounds. The deoxyribose assay showed that hydroxyl radicals were generated during the oxidation of salsolinol in the presence of Cu,Zn-SOD. Therefore, the results indicate that free radical may play a role in the modification and inactivation of Cu,Zn-SOD by salsolinol.     

Presence of methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines, derivatives of the neurotoxin isoquinoline, in parkinsonian lumbar CSF.

The TIQ derivatives 2-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (2-MDTIQ) and 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (1-MDTIQ, salsolinol) were identified the first time as possible endogenous neurotoxins in parkinsonian but not in normal human lumbar cerebrospinal fluid by high performance liquid chromatography with electrochemical detection. Additionally, MDTIQ analogues were incubated with a monoamine oxidase (MAO) assay. MAO was able to metabolize dose-dependently 2-MDTIQ, whereas 1-MDTIQ was not modified by the enzyme.     

Salsolinol, a derivate of dopamine, is a possible modulator of catecholaminergic transmission: a review of recent developments

Catecholamine (dopamine, norepinephrine and epinephrine) synthesizing neurons are widely distributed in the brain, sympathetic ganglia and throughout peripheral organs. Results of several recent experiments clearly suggest that many of these neurons can also contain 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), a derivate of dopamine. However, direct proof of salsolinol synthesis in those neurons is still missing. The data obtained with administration of exogenous salsolinol strongly indicate that it may play an important role in catecholaminergic regulatory processes, such as the regulation of prolactin release and/or neuronal transmission in sympathetic ganglia. Several recent data have also indicated a relationship between salsolinol or its metabolites and the etiology of Parkinson's disease or neuropathology of chronic alcoholism. These seemingly different roles of salsolinol will be discussed separately, but some common features will also be highlighted. Based on all of the discussed data the existence of a "salsolinolergic" system using salsolinol as a neuromodulator, which may be present in catecholamine synthesizing neurons, is postulated.     

Salsolinol,a catechol neurotoxin,induces oxidative modification of cytochrome c

Methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), an endogenous neurotoxin, is known to perform a role in the pathogenesis of Parkinson’s disease (PD). In this study, we evaluated oxidative modification of cytochrome c occurring after incubation with salsolinol. When cytochrome c was incubated with salsolinol, protein aggregation increased in a dosedependent manner. The formation of carbonyl compounds and the release of iron were obtained in salsolinol- treated cytochrome c. Salsolinol also led to the release of iron from cytochrome c. Reactive oxygen species (ROS) scavengers and iron specific chelator inhibited the salsolinol-mediated cytochrome c modification and carbonyl compound formation. It is suggested that oxidative damage of cytochrome c by salsolinol might induce the increase of iron content in cells, subsequently leading to the deleterious condition which was observed. This mechanism may, in part, provide an explanation for the deterioration of organs under neurodegenerative disorders such as PD. [BMB Reports 2013; 46(2): 119-123]     

ACTIVITIES OF 3,4-DIHYDROXY-l-PHENYLALANINE AND 5-HYDROXY-l-TRYPTOPHAN DECARBOXYLASES IN RAT BRAIN: ASSAY CHARACTERISTICS AND DISTRIBUTION

Abstract— Optimal assay conditions for decarboxylation of 3,4-dihydroxy- l -phenylalanine (DOPA) and 5-hydroxy- l -tryptophan (5-HTP) were determined in homogenates of rat brain by use of a sensitive, precise microradiometric technique. The two activities exhibited widely different optima for pH, temperature and substrate concentrations. The activity of 5-HTP decarboxylase was stimulated 2-fold by added pyridoxal-5-phosphate and was relatively resistant to antagonists of pyridoxal-P. By contrast, the activity of DOPA decarboxylase was stimulated 20-fold by added coenzyme and could be completely inhibited by carboxyl trapping agents. DOPA decarboxylase activity in subcellular fractions of brain was associated predominately with the soluble fractions and its distribution in the various fractions closely paralleled that of lactic acid dehydrogenase. 5-HTP decarboxylase activity in brain was distributed almost equally between soluble and particulate fractions, and its distribution within the particulate fractions differed from that of succinic acid dehydrogenase. The two decarboxylases in brain exhibited a 7-fold divergence in relative specific activity when their respective distributions in subcellular fractions were compared. Similarly, the regional distributions of the two decarboxylases in rat brain did not parallel one another; e.g. there was a 4-fold difference between the ratio of the two activities in cerebellum and that found in the corpus striatum.     

Conversion of DOPA to tetrahydroisoquinolines and stizolobic acid in a callus culture of Stizolobium hassjoo

Isolation and identification of l-3-carboxy-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline and l-1-methyl-3-carboxy-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline from seeds and callus of S. hassjoo are described. Administration of [β-¹⁴C]-labelled DOPA to a callus culture of this legume resulted in the incorporation of radioactivity into l-3-carboxy-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, l-1-methyl-3-carboxy-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline and stizolobic acid, which was confirmed by constant specific radioactivity after co-crystallization with authentic samples of each compound.     

Excitatory Amino Acids: Studies on the Biochemical and Chemical Stability of Ibotenic Acid and Related Compounds

The complex pharmacological profile (excitation/inhibition) of ibotenic acid on single neurons in the mammalian CNS prompted studies on the stability of ibotenic acid and a number of structurally related excitatory amino acids under different in vitro conditions in the presence or absence of enzymes. Ibotenic acid, (RS)-3-hydroxy-4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-7-carboxylic acid (7-HPCA), (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and (RS)-alpha-amino-3-hydroxy-4-bromo-5-isoxazolepropionic acid (4-Br-homoibotenic acid) were all inhibitors of (S)-glutamic acid decarboxylase (GAD) in mouse brain homogenates, but only ibotenic acid was shown to undergo decarboxylation during incubation with brain homogenates. The formation of the decarboxylated product, muscimol, which primarily occurred in a synaptosomal fraction, was dependent on the presence of pyridoxal-5-phosphate (PALP) and was inhibited by (S)-glutamic acid, 3-mercaptopropionic acid (3MPA), aminooxyacetic acid (AOAA), and allyglycine, suggesting that ibotenic acid is a substrate for GAD. The overall decomposition rate for ibotenic acid (8.7 nmol min-1 mg-1 of protein), which apparently embraces other reactions in addition to decarboxylation to muscimol, was higher than the rate of decarboxylation of (S)-glutamic acid (3.2 nmol min-1 mg-1 of protein). At pH 7.4 and 37 degrees C, but in the absence of enzymes, none of the excitatory amino acids under study underwent any detectable decomposition, whereas ibotenic acid and 7-HPCA, but not AMPA and 4-Br-homoibotenic acid, decomposed, partially by decarboxylation, at 100 degrees C in a pH-dependent manner. In the presence of liver homogenates, ibotenic acid was also shown to decompose.(ABSTRACT TRUNCATED AT 250 WORDS)     

Selective 7-O-methylation of salsolinol in rat brain and heart in vivo

Intracerebroventricular and intraperitoneal injections of salsolinol and subsequent analyses of rat brain and heart revealed that 7-O-methylsalsolinol (7-OMe-Sal) is the principal O-methylated product formed in vivo. Production of 7-OMe-Sal was blocked by pretreatment of the rats with pyrogallol, an inhibitor of catechol-O-methyltransferase. 7-OMe-Sal and 6-O-methylsalsolinol (6-OMe-Sal) injected intraventricularly or prepared as external standards were distinguished by gas chromatography as peaks with different relative retention times compared to salsolinol as an internal standard. These substances were chromatographed as their corresponding pentafluoropropionic anhydride derivatives on a JXR column. Similar experiments performed with 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline revealed that this substance was similarly selectively converted to its 7-O-methylated product in rat brain.     

Catecholamine-Derived Tetrahydroisoquinolines: O-Methylation Patterns and Regional Brain Distribution Following Intraventricular Administration in Rats

Abstract: The metabolism of 6,7-dihydroxy (catecholic) -1,2,3,4-tetrahydroisoquinoIines (TIQs) is of interest because the heterocyclic substances may form in mammals normally or during certain diseases via condensations of catecholamines (CAs) with aldehydes or α-keto acids. With a specific capillary gas chromatography procedure and confirmatory liquid chromatographic assays, we have determined the structural isomers and relative amounts of mono-O-methylated (phenolic) TIQ metabolites in several rat brain regions 40 min following the acute intracerebroventricular injection of four structurally related catecholic TIQs. In sharp contrast with the established selective m-O-methylation of dopamine (DA) by catechol-O-methyltransferase in brain, the two simple TIQs derived from DA produced predominantly or even exclusively the metabolic isomer arising from methylation of the original p-hydroxyl group (7-O-methylation). In three catecholaminergic brain regions examined, the 7-O-methyl isomer was the only detectable phenolic metabolite of (±) salsolinol-1-carboxylic acid (a condensation product of DA and pyruvic acid) and, as first noted by Bail et al. (1980), constituted 95% of the two possible isomeric mono-O-methyl metabolites of (±) salsolinol (TIQ derivative of DA and acetaldehyde). Though less, the 7-O-methyl isomers still were a significant proportion (40–55%) of the two mono-O-methylated metabolites of (±) 4-hydroxy-desmethylsalsolinol (a TIQ derived from norepinephrine and formaldehyde), or of the DOPA/acetaldehyde-derived TIQ, (cis) salsolinol-3-carboxylic acid. In the time frame of the study, all four administered TIQs showed higher levels in hypothalamus than in striatum or hippocampus, with the two carboxylated alkaloids displaying the greatest differences. However, for a given TIQ, the proportion present as mono-O-methyl metabolite(s) and the O-methyl isomer distribution did not differ across the three brain regions, indicating that O-methylation involved a single homogenous enzyme that was not saturated in vivo at the concentrations attained by the heterocyclic catechols. The most notable findings, that of exclusive methylation on the original p-hydroxyl group of a physiologically relevant CA derivative, and an O-methylation pattern that appeared dependent on the substituents on the heterocyclic ring, are explained on the basis of an important hydrophobic binding site in catechol-O-methyltransferase in vivo.     

Isolation and characterization of basic superoxide dismutase consisting of Mr-25,000 subunits in rat liver

1. A basic protein (pI = 9.0) exhibiting superoxide dismutase activity was purified to homogeneity from rat liver by DEAE-cellulose, CM-cellulose and S-hexylglutathione affinity gel chromatography, chromatofocusing and Sephadex G-150 gel filtration. 2. The purified enzyme had specific activity of 4700 units/mg protein. The activity was not affected by 2 mM KCN. Manganese was detected in the enzyme preparation; the content was 0.9 mol/mol subunit. The N-terminal sequence of the first 23 amino acids of the enzyme exhibited a strong homology (except at position 11) with the mature protein of human Mn-superoxide dimutase. It is, therefore, concluded that the purified enzyme is Mn-superoxide dismutase. 3. The N-terminal amino acid sequence showed that about 50% of tyrosine at position 11 was substituted by glutamine, suggesting the existence of microheterogeneity of the superoxide dismutase protein. 4. The superoxide dismutase purified here was found to consist of subunits with an apparent relative molecular mass of 25,000. This larger than the value hitherto reported for rat liver Mn-superoxide dismutase (Mr 2,400); the previous low value is attributed to differences in methods. 5. The enzyme was shown by immuno-blotting to be exclusively localized in the mitochondrial fraction in the liver. The tissue content of Mn-superoxide dismutase is organ-specific, and was the highest in heart. The precursor protein of the Mn-superoxide dismutase was not detectable in the liver cytosolic and mitochondrial fractions as well as in several extrahepatic organs (lung, heart, brain, muscle, kidney and testis), suggesting rapid transport across mitochondrial membranes and processing of the superoxide dismutase protein.     

Increased Levels of Monoamine-Derived Potential Neurotoxins in Fetal Rat Brain Exposed to Ethanol

Pregnant SD rats were exposed to ethanol (25 % (v/v) ethanol at 1.0, 2.0 or 4.0 g/kg body weight from GD8 to GD20) to assess whether ethanol-derived acetaldehyde could interact with endogenous monoamine to generate tetrahydroisoquinoline or tetrahydro-beta-carboline in the fetuses. The fetal brain concentration of acetaldehyde increased remarkably after ethanol administration (2.6 times, 5.3 times and 7.8 times as compared to saline control in 1.0, 2.0 and 4.0 g/kg ethanol-treated groups, respectively) detected by HPLC with 2,4-dinitrophenylhydrazine derivatization. Compared to control, ethanol exposure induced the formation of 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol, Sal), N-methyl-salsolinol (NMSal) and 1-methyl-6-hydroxy-1,2,3,4-tetrahydro-beta-carboline (6-OH-MTHBC) in fetal rat brains. Determined by HPLC with electrochemical detector, the levels of dopamine and 5-hydroxytryptamine in whole fetal brain were not remarkably altered by ethanol treatment, while the levels of homovanillic acid and 5-hydroxyindole acetic acid in high dose (4.0 g/kg) of ethanol-treated rats were significantly decreased compared to that in the control animals. 4.0 g/kg ethanol administration inhibited the activity of mitochondrial monoamine oxidase (51.3 % as compared to control) and reduced the activity of respiratory chain complex I (61.2 % as compared to control). These results suggested that ethanol-induced alteration of monoamine metabolism and the accumulation of dopamine-derived catechol isoquinolines and 5-hydroxytryptamine-derived tetrahydro-beta-carbolines may play roles in the developmental dysfuction of monoaminergic neuronal systems.     

Biosynthesis of beta-glucuronides of retinol and of retinoic acid in vivo and in vitro

After the intraportal injection of retinol-6,7-(14)C to rats, the O-ether derivative of retinol, retinyl -glucosiduronate, appears in the bile. Both retinoyl -glucuronide and retinyl -glucosiduronate are also synthesized in vitro when washed rat liver microsomes are incubated with uridine diphosphoglucuronic acid (UDPGA) and either retinoic acid or retinol, respectively. The synthesis of retinoyl -glucuronide was also demonstrated in microsomes of the kidney and in particulate fractions of the intestinal mucosa. The glucuronides were characterized by their UV absorption spectra, by their quenching of UV light or fluorescence under it, by their thin-layer chromatographic behavior in two solvent systems, and by the identification of products released during their hydrolysis by -glucuronidase. With retinoic acid as the substrate, the UDP glucuronyl transferase of rat liver microsomes had a pH optimum of 7.0, a temperature optimum of 38 degrees C, and a marked dependence on the concentrations of both retinoic acid and UDPGA, but was unaffected by a number of possible inhibitors, protective agents, and competitive substrates. The conversion of retinal to retinoic acid and the synthesis of retinoyl -glucuronide from retinoic acid could not be detected in whole homogenates, cell fractions, or outer segments of the bovine retina.     

Naphthalenes and naphthoquinones from Ventilago species

Two new naphthalene derivatives and three naphthoquinones have been found in the root bark of Ventilago maderaspatana. Their structures are 2-acetyl-6,7-dimethoxy-3-methyl-1,8-methylenedioxynaphthalene (ventilaginone) and 1,3-dihydro-6,9-dihydroxy-7,8-dimethoxy-1-methylnaphtho[2,3-c]furan-3-one (ventilagol), 2(2′-acetoxypropyl)-3-hydroxy-5,7,8-trimethoxy-1,4-naphthoquinone (maderone), cordeauxione and isocordeauxione. The root bark of V. calyculata contains 2-methoxystypandrone and 1-hydroxy-6-methoxy-3-methylxanthone-8-carboxylic acid (calyxanthone).     

Possible role of salsolinol quinone methide in the decrease of RCSN-3 cell survival

The endogenous dopamine-derived neurotoxin salsolinol was found to decrease survival in the dopaminergic neuronal cell line RCSN-3, derived from adult rat substantia nigra in a concentration-dependent manner (208 microM salsolinol induced a 50% survival decrease). Incubation of RCSN-3 cells with 100 micro;M dicoumarol and salsolinol significantly decreased cell survival by 2.5-fold (P < 0.001), contrasting with a negligible effect on RCHT cells, which exhibited nearly a 5-fold lower nomifensine-insensitive dopamine uptake. The levels of catalase and glutathione peroxidase mRNA were decreased when RCSN-3 cells were treated with 100 microM salsolinol alone or in the presence of 100 microM dicoumarol. In vitro oxidation of salsolinol to o-quinone catalyzed by lactoperoxidase gave the quinone methide and 1,2-dihydro-1-methyl-6,7-isoquinoline diol as final products of salsolinol oxidation as determined by NMR analysis. Evidence of the formation of salsolinol o-semiquinone radical has been provided by ESR studies during one-electron oxidation of salsolinol catalyzed by lactoperoxidase.     

Oxidative DNA damage and glioma cell death induced by tetrahydropapaveroline

A series of naturally occurring isoquinoline alkaloids, besides their distribution in the environment and presence in certain food stuffs, have been detected in human tissues including particular regions of brain. An example is salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline) that not only induces neuronal cell death, but also causes DNA damage and genotoxicity. Tetrahydropapaveroline [THP; 6,7-dihydroxy-1-(3',4'-dihydroxybenzyl)-1,2,3,4-tetrahydroisoquinoline], a dopamine-derived tetrahydroisoquinoline alkaloid, has been reported to inhibit mitochondrial respiration and is considered to contribute to neurodegeneration implicated in Parkinson's disease. Since THP bears two catechol moieties, the compound may readily undergo redox cycling to produce reactive oxygen species (ROS) as well as toxic quinoids. In the present study, we have examined the capability of THP to cause oxidative DNA damage and cell death. Incubation of THP with phiX174 supercoiled DNA or calf thymus DNA in the presence of cupric ion caused substantial DNA damage as determined by strand scission or formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), respectively. THP plus copper-induced DNA damage was ameliorated by some ROS scavengers/antioxidants and catalase. Treatment of C6 glioma cells with THP led to a concentration-dependent reduction in cell viability, which was prevented by the antioxidant N-acetyl-L-cysteine. When these cells were treated with 10microM THP, c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) were rapidly activated via phosphorylation, whereas activation of extracellular signal-regulated protein kinase (ERK) was inhibited. Furthermore, pretreatment with inhibitors of JNK and p38 MAPK rescued the glioma cells from THP-induced cytotoxicity, suggestive of the involvement of these kinases in THP-induced C6 glioma cell damage.     

Xanosporic acid,an intermediate in bacterial degradation of the fungal phototoxin cercosporin

The red fungal perylenequinone phototoxin cercosporin is oxidized by Xanthomonas campestris pv zinniae to a non-toxic, unstable green metabolite xanosporic acid, identified via its lactone as 1,12-bis(2'R-hydroxypropyl)-4,9-dihydroxy-6,7-methylenedioxy-11-methoxy-3-oxaperylen-10H-10-one-2-carboxylic acid. Xanosporolactone was isolated in approximately 2:1 ratio of M:P atropisomers.     

The role of catecholamines in the prolactin release induced by salsolinol

Salsolinol (1,2,3,4-tetrahydro-6,7-dihydroxy-1-methylisoquinoline) is an endogenous prolactin releasing agent. Its action can be inhibited by another isoquinoline, 1-methyl-3,4-dihydroisoquinoline (1MeDIQ), which has a strong norepinephrine releasing activity. Salsolinol does not alter the dopamine release in median eminence in vitro, providing evidence for the lack of interaction with presynaptic D2 dopamine receptors. At the same time, lack of norepinephrine transporter abolishes salsolinol's action. Salsolinol decreases tissue level of dopamine and increases norepinephrine to dopamine ratio in organs innervated by the sympathetic nervous system indicating a possible decrease of norepinephrine release. Enzymes of catecholamine synthesis and metabolism are probably also not the site of action of salsolinol. In summary, based upon all of these observations a physiologically relevant interplay might exist between the sympatho-neuronal system and the regulation of prolactin release.     

Quantitative determination of endogenous tetrahydroisoquinoline salsolinol in peripheral blood mononuclear cells by gas chromatography–mass spectrometry

Endogenous 1-methyl-1, 2, 3, 4-tetrahydro-6,7-dihydroxyisoquinoline (salsolinol) could be a potential marker involved in the etiology of alcoholism. The amount of salsolinol analyzed previously from plasma and urine by different methods depends on several dietary conditions because nutrition has an important influence on salsolinol excretion. Whereas plasma salsolinol is influenced by the diet the salsolinol from peripheral mononuclear cells should be endogenously formed. Therefore, a method for the quantification of S-and R-salsolinol from lymphocytes by using gas chromatography–mass spectrometry was developed. The average amount of salsolinol in 10⁶ cells was 1.25 ng corresponding to 2.41×10⁻⁵ M and was shown to be much higher than the plasma salsolinol concentration (2.6×10⁻⁹ M).