Conversion of 3, 4-dihydroxyphenylalanine and deuterated 3, 4-dihydroxyphenylalanine to alcoholic metabolites of catecholamines in rat brain

Nutraceutical Role of Polyphenols and Triterpenes Present in the Extracts of Fruits and Leaves of Olea europaea as Antioxidants, Anti-Infectives and Anticancer Agents on Healthy Growth

There is currently a worldwide consensus and recognition of the undoubted health benefits of the so-called Mediterranean diet, with its intake being associated with a lower risk of mortality. The most important characteristics of this type of diet are based on the consumption of significant amounts of fruit, vegetables, legumes, and nuts, which provide, in addition to some active ingredients, fiber and a proportion of vegetable protein, together with extra virgin olive oil (EVOO) as the main sources of vegetable fat. Fish and meat from poultry and other small farm animals are the main sources of protein. One of the main components, as already mentioned, is EVOO, which is rich in monounsaturated fatty acids and to a lesser extent in polyunsaturated fatty acids. The intake of this type of nutrient also provides an important set of phytochemicals whose health potential is widely spread and agreed upon. These phytochemicals include significant amounts of anthocyanins, stilbenes, flavonoids, phenolic acids, and terpenes of varying complexities. Therefore, the inclusion in the diet of this type of molecules, with a proven healthy effect, provides an unquestionable preventive and/or curative activity on an important group of pathologies related to cardiovascular, infectious, and cancerous diseases, as well as those related to the metabolic syndrome. The aim of this review is therefore to shed light on the nutraceutical role of two of the main phytochemicals present in Olea europaea fruit and leaf extracts, polyphenols, and triterpenes, on healthy animal growth. Their immunomodulatory, anti-infective, antioxidant, anti-aging, and anti-carcinogenic capabilities show them to be potential nutraceuticals, providing healthy growth.

Have we been ignoring the elephant in the room? Seven arguments for considering the cerebellum as part of addiction circuitry

Addiction involves alterations in multiple brain regions that are associated with functions such as memory, motivation and executive control. Indeed, it is now well accepted that addictive drugs produce long-lasting molecular and structural plasticity changes in corticostriatal-limbic loops. However, there are brain regions that might be relevant to addiction other than the prefrontal cortex, amygdala, hippocampus and basal ganglia. In addition to these circuits, a growing amount of data suggests the involvement of the cerebellum in many of the brain functions affected in addicts, though this region has been overlooked, traditionally, in the addiction field. Therefore, in the present review we provide seven arguments as to why we should consider the cerebellum in drug addiction. We present and discuss compelling evidence about the effects of drugs of abuse on cerebellar plasticity, the involvement of the cerebellum in drug-induced cue-related memories, and several findings showing that the instrumental memory and executive functions also recruit the cerebellar circuitry. In addition, a hypothetical model of the cerebellum's role relative to other areas within corticostriatal-limbic networks is also provided. Our goal is not to review animal and human studies exhaustively but to support the inclusion of cerebellar alterations as a part of the physiopathology of addiction disorder.

Oleuropein and derivatives from olives as Tau aggregation inhibitors

Tau isoforms constitute a family of microtubule-associated proteins that are mainly expressed in neurons of the central nervous system. They promote the assembly of tubulin monomers into microtubules and modulate their stability, thus playing a key structural role in the distal portion of axons. In Alzheimer's disease and related tauopathies, Tau aggregation into fibrillary tangles contributes to intraneuronal and glial lesions. We report herein the ability of three natural phenolic derivatives obtained from olives and derived food products to prevent such Tau fibrillization in vitro, namely hydroxytyrosol, oleuropein, and oleuropein aglycone. The latter was found to be more active than the reference Tau aggregation inhibitor methylene blue on both wild-type and P301L Tau proteins, inhibiting fibrillization at low micromolar concentrations. These findings might provide further experimental support for the beneficial nutritional properties of olives and olive oil as well as a chemical scaffold for the development of new drugs aiming at neurodegenerative tauopathies.

Hydroxytyrosol: from laboratory investigations to future clinical trials

Mediterranean countries have lower rates of mortality from cardiovascular disease and cancer than Northern European or other Western countries. This has been attributed, at least in part, to the so-called Mediterranean diet, which is composed of specific local foods, including olive oil. Traditionally, many beneficial properties associated with this oil have been ascribed to its high oleic acid content. Today, it is clear that many of the beneficial effects of ingesting virgin olive oil are due to its minor compounds. This review summarizes the existing knowledge concerning the chemistry, pharmacokinetics, and toxicology of hydroxytyrosol, a minor compound of virgin olive oil, as well as this compound's importance for health. The main findings in terms of its beneficial effects in cardiovascular disease and cancer, including its properties against inflammation and platelet aggregation, are emphasized. New evidence and strategies regarding the use of hydroxytyrosol as a natural drug for the prevention and treatment of diseases with high incidences in Western countries are also presented.

Localization of L-DOPA uptake and decarboxylating neuronal structures in the cat brain using dopamine immunohistochemistry

The present study examined dopamine-immunoreactive neuronal structures using immunohistochemistry in conjunction with an anti-dopamine antiserum, following injection of l-3,4-dihydroxyphenylalanine (L-DOPA) with or without an inhibitor of monoamine oxidase (Pargyline) in the cat brain. L-DOPA injection made it possible to detect dopamine immunoreactivity in presumptive serotonergic and noradrenergic cell bodies and axons. Weak to moderate dopamine immunoreactivity was observed in non-aminergic cells (possibly so-called "D" cells containing aromatic L-amino acid decarboxylase (AADC)) in several hypothalamic, midbrain, pontine and medullary nuclei. Intense dopamine immunoreactivity became visible in a large number of cells and axons (possibly containing AADC) with wide distribution in the brain following administration of L-DOPA with Pargyline. AADC is most likely active in cells and axons that take up L-DOPA, where it decarboxylates the L-DOPA to dopamine. However, newly synthesized dopamine in such cells is rapidly oxidized by monoamine oxidase.

An endogenous metabolite of dopamine, 3,4-dihydroxyphenylethanol, acts as a unique cytoprotective agent against oxidative stress-induced injury

A natural compound contained in olive oil, 3,4-dihydroxyphenylethanol (DOPE), is also known as an endogenous metabolite of dopamine. The role of DOPE in oxidative stress-induced cell damage was investigated using differentiated PC12 cells. Superoxide (O(2)(-)) and H(2)O(2) induced a dose-dependent leakage of lactate dehydrogenase (LDH) and decreased cell viability denoted by MTT assay. While O(2)(-) -induced cell damage was not affected by DOPE, pretreatment of the cells with DOPE dose-dependently prevented the leakage of LDH induced by H(2)O(2). In these cells, augmented activity of catalase was demonstrated, while the levels of glutathione and glutathione peroxidase activity remained unchanged. The effect of DOPE was abolished when an inhibitor of catalase 3-amino-l, 2,4-triazole, was included in the medium. DOPE also protected against cell damage induced by H(2)O(2), and Fe(2+). In the hydroxyl radical ((.-)OH) assay using p-nitroso-N, N-dimethylaniline (PNDA), oxidation of PNDA by (.-)OH generated by the Fenton reaction was significantly attenuated in the presence of DOPE. By an electron spin resonance spin trapping study that represents the direct activity of DOPE to scavenge (.-)OH, however, limited scavenging activity was demonstrated for DOPE. Taken together, DOPE may act as a unique cytoprotective compound in nerve tissue subjected to oxidative stress.

The effect of acute, chronic and chronic intermittent stress on the central noradrenergic system

The objective of this investigation was to examine the immediate and long term effects of acute, chronic and chronic intermittent stress on the central noradrenergic system of rats. Male Sprague-Dawley rats were subjected to one hour of physical immobilization stress either as a single exposure, or as 14 exposures applied either on consecutive days, or randomly over 60 days. Animals were sacrificed immediately, 6 h and 24 h following the last stressor. Levels of norepinephrine (NE) and 3-methoxy-4-hydroxyphenylethylene-glycol sulfate (MHPG-sulfate) were measured in the hypothalamus, hippocampus, cerebral cortex and locus coeruleus region and beta-adrenergic receptor (BAR) density was determined in the cortex. Immediately after acute stress, a significant reduction in hypothalamic NE levels and marked increases in MHPG-sulfate levels in all four brain regions were observed. In contrast immediately after the last stressor of a chronic or chronic intermittent stress regimen, no change in NE concentration was observed while levels of MHPG-sulfate in the four brain regions showed a smaller increase than that observed after an acute stressor. Acute stress induced changes normalized within 6 h while chronic and chronic intermittently stressed animals had altered NE or MHPG-sulfate levels in certain brain regions for up to 6-24 h. Cortical BAR binding parameters remained unchanged after all stress paradigms.

Vesicular accumulation of dopamine following L-DOPA administration

In this study, the accumulations of dopamine (DA) and norepinephrine (NE) were measured in the brain tissues and in the synaptic vesicle fractions prepared from whole brain of control rats and rats injected with L-DOPA. In the normal rat brain, a 3-fold increase in DA following L-DOPA administration was followed by a small, but not significant increase in vesicular DA, indicating a restricted vesicular uptake of exogenous DA. At the same time, NE in the vesicular fraction and in the whole brain tissue did not change, suggesting a possible link between DA vesicular uptake of DA and brain NE. However, in rats pretreated with alpha-methyl-p-tyrosine, which significantly (P less than 0.05) reduced DA and NE levels in brain tissues and in the synaptic vesicles, L-DOPA administration led to a significant increase in vesicular DA (P less than 0.05), suggesting that catecholamine depletion may result in greater vesicular uptake of cytoplasmic DA. The increase in vesicular DA was accompanied by increases in tissue and vesicular NE, underscoring again the existence of a link between vesicular uptake of DA and brain NE following L-DOPA administration. The results also demonstrated a large increase in 3,4-dihydroxyphenylacetic acid (DOPAC) following L-DOPA, in the brain tissues but not in the synaptic vesicle, indicating that monoamine oxidase activity is confined to the cytoplasm.

Dopamine and memory function in Parkinson's disease

Response fluctuations in motor function, complicating long-term dopaminomimetic therapy of Parkinson's disease, may extend to the cognitive realm. To evaluate the effect of levodopa treatment both on attention as well as acquisition and retrieval of memory tasks, parkinsonian patients were examined neuropsychologically both while medicated with levodopa/carbidopa ("on") and when the medication's antiparkinsonian effect had worn off ("off"). Significant cognitive differences emerged only on the delayed recall of complex verbal materials, where patients when "on" performed better compared with their "off" state. Comparison of change scores across states (administration or withholding of levodopa/carbidopa between acquisition and retrieval, "off" to "on" or "on" to "off"), revealed no substantial differences as a function of dopaminomimetic therapy. These results support the view that slight changes in cognition are associated with dopaminomimetic therapy of Parkinson's disease, but that these changes may be task-specific.

On the mechanism of imipramine's influence in lowering p-hydroxyphenylglycol concentrations in the brain. The role of tyrosine

Administration of imipramine (IMI) to rats was shown to lower after 4.5 hr the brain concentration of the octopamine metabolite p-hydroxyphenylglycol (pHPG) in a dose-dependent manner over the range of 10-40 mg/kg of IMI. Assay of plasma and brain levels of tyrosine revealed that IMI produced a reduction in both but with a shorter time-course than for the depletion in pHPG, with the maximal decreases occurring at 1.5 hr, before there was any loss of pHPG. The reductions in tyrosine and pHPG levels could not be explained by an effect of IMI on food intake, since the levels were diminished even in 24-hr fasted animals. When rats were injected with IMI 4.5 hr before 200 mg/kg of tyrosine and 5.5 hr before being killed, the elevation in brain pHPG levels were attenuated by about 50%, as compared to the animals that received tyrosine alone. These data suggest that the ability of IMI to lower brain pHPG probably involves two distinct mechanisms: (1) a lowering of brain and plasma tyrosine concentrations, and (2) an inhibition of the conversion of tyrosine to pHPG. It is unclear whether these effects are due to IMI itself or to one of its metabolites, such as desmethylimipramine or didesmethylimipramine, which were found in the plasma in amounts equal to or greater than IMI.

Increase in mouse brain regional noradrenaline turnover after L-dopa administration

Noradrenaline (NA) and its major metabolite, 3-methyl-4-hydroxyphenylethylene glycol (MHPG) were measured by HPLC with electrochemical detection in five mouse brain regions after L-dopa treatment. Noradrenaline concentration increased significantly, by 30-40%, in the three terminal regions of the locus coeruleus; cortex, hippocampus and cerebellum, but did not change in hypothalamus and brainstem. In mice whose central NA levels had been depleted by prior treatment with the neurotoxin, DSP-4, remaining NA neurons in these terminal regions were still able to respond with an increase in NA after L-dopa loading. The NA metabolite, MHPG, increased several-fold in all five regions in both saline and DSP-4-pretreated mice. Thus, L-dopa may be a useful precursor of NA in specific brain regions, particularly when NA is depleted.

A new method for the determination of L-dopa and 3-O-methyldopa in plasma and cerebrospinal fluid using gas chromatography and electron capture negative ion mass spectrometry

L-3-(3,4-Dihydroxyphenyl)alanine (DOPA) and its 3-O-methyl metabolite (OMD) were measured in plasma and cerebrospinal fluid by a new assay which combines N,O-acetylation of amino acids in aqueous media, preparation of pentafluorobenzyl esters under anhydrous conditions, and analysis by gas chromatography-electron capture negative ion mass spectrometry. The N,O-acetyl, carboxy-PFB derivatives gave abundant carboxylate anions ([M-CH2C6F5]-) which were suitable for sensitive analysis using selected ion monitoring. Plasma and CSF samples were sufficiently purified by a simple organic solvent extraction. Analytical recovery for DOPA was 100.2 +/- 3.7% at the level of 100 nmol/l. Analysis of DOPA in plasma was performed with a relative standard deviation of 5%. The limit of quantitation in plasma and CSF was at the sub-nmol/l level. In healthy adults, DOPA concentration in plasma was 9.0 +/- 2 nmol/l (n = 11) and in CSF 3.5 +/- 0.9 nmol/l (n = 9). The concentration of OMD in plasma was 99.1 nmol/l (pool of 24 samples) and 15.3 nmol/l in CSF (pool of 12 samples). Measurement of 5-[2H]DOPA and 5-[2H]OMD in plasma of a healthy individual who had been orally loaded with 3,5-[2H2]tyrosine (150 mg kg body wt) was possible for several hours after the load.

Modification of dopamine and norepinephrine metabolism in the rat brain by monoamine oxidase inhibitors

The treatment of Sprague-Dawley rats with monoamine oxidase (MAO) inhibitors (pargyline, tranylcypromine) profoundly affects dopamine (DA) and norepinephrine (NE) metabolism in the brain. In these rats injection of L-dopa led to large increases in norepinephrine (NE), normetanephrine (NMN) and 3-methoxytyramine (3-MT) in brain tissues. The response of MAO-inhibited rats to L-dopa contrasted sharply with those not treated with the MAO inhibitor; the latter showed no change in NE, NMN and 3-MT after similar administration of L-dopa. The increase of NE in pargyline-treated rats correlated closely with that of DA in the hypothalamus and in the brain stem. This response was greatly diminished in rats previously treated with the neurotoxin 6-hydroxydopamine, but was restored when the treatment with 6-hydroxydopamine was accompanied by desimipramine. This suggests that noradrenergic neurons were the origin of the NE response. The NMN and 3-MT increases occurring only in the rats treated with a MAO inhibitor were highly correlated. The results suggested that MAO inhibitor may affect entry of DA into catecholaminergic storage where NE synthesis takes place and from where DA is released.

Effects of debrisoquin on the excretion of catecholamine and octopamine metabolites in the rat and guinea pig

The effects of debrisoquin, administered daily for 4 days to rats (40 mg/kg, i.p.) and guinea pigs (4 mg/kg, i.p.), were determined for urinary excretion of several acidic and neutral amine metabolites, including the norepinephrine metabolites, 3-methoxy-4-hydroxyphenethylene glycol (MHPG) and vanillylmandelic acid (VMA), the dopamine metabolites, 3,4-dihydroxyphenethanol (DHPE), 3-methoxy-4-hydroxyphenethanol (MHPE), and homovanillic acid (HVA), and the octopamine metabolite, p-hydroxyphenylglycol (pHPG). The excretion of MHPG was reduced to 32% of control in rats and to 46% in guinea pigs, HVA was reduced to 64 and 80% in these two species, respectively, and MHPE was lowered to 59% of control in the rat but was not affected in the guinea pig. DHPE and pHPG were not altered significantly in either species. VMA was a minor metabolite in both species, being less than 6% of MHPG, and its formation was blocked only partially (rat) or not at all (guinea pig) by debrisoquin. The data refute the idea based on previous in vitro studies that VMA is a major metabolite of norepinephrine in the periphery of the guinea pig as it is in man.

The effects of imipramine and iprindole on the metabolism of octopamine in the rat

Acute injections of imipramine and iprindole in rats produced significant decreases in the concentration of p-hydroxyphenylglycol (pHPG), a neutral metabolite of octopamine in brain at 6 and 24 hr after the administration of drugs. The 24-hr urinary levels of both free and total pHPG were reduced to 25-29% of control with acute administration of imipramine, while iprindole produced a 30% decrease in free pHPG. With chronic administration of imipramine, concentrations of pHPG in brain returned to normal, while the 24-hr urinary levels were still decreased (to 24%). Octopamine in brain was unaltered after both single and repeated injections of imipramine. Thus, these data suggest that the turnover of octopamine in brain is reduced after acute administration of imipramine and iprindole, while after chronic treatment with imipramine, turnover of octopamine in brain has returned to control levels.

Opposite effects of chronic imipramine treatment on brain and urine MHPG levels in the rat

Acute imipramine (IMI; 20 mg/kg, ip) in rats decreased the brain concentration of 3-methoxy-4-hydroxyphenethylene glycol (MHPG), a metabolite of norepinephrine (NE), to 85% of control 24 hr after injection. In contrast, chronic IMI (20 mg/kg, ip, daily for 14 days) significantly raised brain MHPG levels to 123% of control, while reducing brain NE levels. Urinary MHPG levels were reduced by both acute and chronic IMI treatments, to 52% and 51%, respectively. These data suggest that the brain turnover of NE is reduced after acute IMI, but is elevated after chronic treatment. Although urinary levels of MHPG changed in parallel with brain levels following an acute administration of IMI, such was not the case after chronic administration. We conclude that caution must be used in extrapolating drug-induced changes in urinary metabolite levels to brain amine function.

Effects of intraventricular injections of 6-hydroxydopamine on amine metabolites in rat brain and urine

The effects in rats of intraventricular injections of 6-hydroxydopamine (6-OHDA) on the urinary excretion 1-3 weeks later of 3-methoxy-4-hydroxyphenethylene glycol (MHPG), 3,4-dihydroxyphenethanol (DHPE), 3-methoxy-4-hydroxyphenethanol (MHPE), p-hydroxyphenylglycol (pHPG), homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were examined. The excretion of MHPG was decreased to 63 and 71% of control on days 7 and 14, respectively, but had returned to control levels by day 23, even though the brain levels were decreased by 87%. Free and total HVA excretion was reduced on both days 7 and 23, but free and total DOPAC was reduced only on day 7. Based on these data, it can be estimated that about 39% of the free and 46% of the total HVA in urine originates in the CNS. The excretion of conjugated HVA was decreased by 70-80%, but this decrease does not support the notion that the conjugated form of HVA is derived principally from the brain and thus serves as a better marker of brain dopamine metabolism, since the level of this metabolite in the brain was not correspondingly decreased but was instead increased. Urinary DOPAC levels were generally more variable and derived to a greater extent from the periphery; therefore, DOPAC appears to be less suitable than HVA as a marker of brain dopamine. The results also indicate that as much as 35% of the urinary MHPG may originate in the CNS, although compensatory changes in catecholamine metabolism in either the brain or in the periphery may have somewhat influenced this estimate. The results also suggest that at least as much pHPG as MHPG in urine derives from the CNS. The data are consistent with the idea that the neutral dopamine metabolites largely derive from the brain, but the relatively small depletion in their brain levels produced by 6-OHDA prevented the exact proportion being determined accurately.

Metabolism of catecholamines in the developing spinal cord of the rat

The metabolism of 3,4-dihydroxyphenylethylamine (DA, dopamine) and norepinephrine (NE) both normally, and after the administration of levo-3,4-dihydroxyphenylalanine (L-DOPA), has been studied in several regions of the developing spinal cord of the rat from fetal day (FD) 16 to the young adult stage. During late fetal (from FD 16) and most of neonatal life [to neonatal day (ND) 20], dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were either just detectable or present in very low concentration in all regions in the untreated developing rat. However, the developing spinal cord possesses an enormous capacity to metabolize the large amounts of DA synthesized from injected L-DOPA. At the end of 1 h after 100 mg/kg i.p. of L-DOPA, DOPAC and HVA are 54 +/- 14 (n = 5) and 16 +/- 5 (n = 5) nmol/g, respectively, in the thoracic zona intermedia in the 12-h-old (ND 0.5) rat. This metabolic capability is already highly developed as early as FD 16, peaks during the first half of neonatal life (ND 4 for DOPAC, and ND 15 for HVA), and is considerably reduced toward the end of neonatal life (approximately ND 28) and in the young adult. Control experiments suggest that a substantial part of this synthesis (from L-DOPA) and metabolism of DA occurs in elements other than the descending monoaminergic nerve fibers. By comparison, the synthesis and metabolism of NE develop more slowly, peak in the latter half of neonatal life, and then decline to the level found in the young adult.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis of catecholamines in the developing spinal cord of the rat

Using mass fragmentographic techniques, the synthesis of dopamine (DA) and norepinephrine (NE) was studied in five functional regions in the spinal cord of the developing rat. Norepinephrine was first detectable in the whole cord on fetal day (FD) 16. Thereafter, there was a rapid increase in synthesis. The fastest rate occurred in the ventral horn. The peak concentration was recorded in the latter half of neonatal life, followed by a decline back to the levels found in the adult cord. The capacity of the developing cord to synthesize NE from injected L-dihydroxyphenylalanine (L-DOPA) increased in concert with its normal synthetic capacity. There was no clear consistent pattern in the development of DA synthesis, with two exceptions: (1) in the cervical dorsal horn (CDH), cervical ventral horn ( CVH ), and thoracic zona intermedia ( TZI ), there was a peak of DA on the day of birth; (2) in all regions there was a peak of DA on neonatal day (ND) 20. At FD 16 (the earliest time studied) the developing cord was capable of considerable synthesis (6.0 nmol/g) of DA from injected L-DOPA. This synthetic capacity developed rapidly, peaked at ND 4, and declined back to the adult levels by ND 20. Control experiments indicate that only about 10% (at best) of the DA synthesized from injected L-DOPA occurs in monoaminergic nerve terminals. Norepinephrine is synthesized exclusively in noradrenergic nerve terminals. The newly synthesized DA and NE are both extensively metabolized in the cord. The results are discussed in relationship to current attempts to understand the functional importance of spinal monoaminergic nerves.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytochemical evidence for the existence of norepinephrine-containing glomus cells in the rat carotid body

Some investigators have postulated that glomus cells of the rat carotid body contain only dopamine (DA), and that the norepinephrine (NE) measured in the carotid body resides only in sympathetic nerve endings and ganglion cells. To investigate this hypothesis, we employed a pharmacologic drug sequence which depleted all carotid body catecholamines and then selectively restored DA levels while keeping NE levels significantly lowered. Analysis of carotid body catecholamines by high performance liquid chromatography (HPLC) validated this drug regimen. Employing this drug treatment, we examined glomus cells after potassium dichromate cytochemical staining in an effort to distinguish those glomus cell vesicles which still contained appreciable amounts of catecholamine, presumably DA. Glomus cells from rats receiving vehicle or L-dopa (100 mg kg-1 ip) alone had 83 and 97% of their cells stained, respectively. However, glomus cells from reserpinized (5 mg kg-1 ip) animals were largely unstained (89%). Carotid bodies from animals treated with reserpine and then, 24 h later, with L-dopa 90 min prior to sacrifice had about 46% of their glomus cells stained while 54% of the cells were unstained. The results of this last group, coupled with our biochemical data which demonstrated that DA levels were comparable to control values but that NE was 80% depleted, suggest that a significant number of glomus cells did not contain enough catecholamine to react with the dichromate. We believe that these unstained cells may normally contain NE and that glomus cells may be of several types, some containing predominantly DA and others NE.

Possible role of octopamine and tyramine in the antihypertensive and antidepressant effects of tyrosine

The administration of a dose of 200 mg/kg of tyrosine (as either the free amino acid or the ethyl ester) increased the 24-hour excretion of p-hydroxyphenethyleneglycol (p-HPG) and p-hydroxyphenylethanol, metabolites of octopamine and tyramine, by 147 and 50%, respectively. One hour after this dose of tyrosine, brain levels of p-HPG and p-hydroxyphenylacetic acid (p-HPA), another metabolite of tyramine, were increased by 82 and 196%, respectively. Pretreatment with Ro4-4602, a peripheral decarboxylase inhibitor, reduced by 50% the tyrosine-induced increases in brain p-HPA levels, suggesting that tyramine was partially formed in the brain parenchyma. Tyrosine caused only slight, but non-significant increases in brain levels of catecholamine metabolites. These results suggest that tyrosine-induced increases in the production of tyramine and octopamine in brain may account for some of the effects of tyrosine, such as its antihypertensive and reported antidepressant properties.

Effects of L-dopa on dopamine and norepinephrine concentrations in rat brain assessed by gas chromatography

A highly specific and sensitive gas chromatographic method has been developed which is capable of determining picogram amounts of dopamine (DA) and norepinephrine (NE) simultaneously. The catecholamines are converted to the N-2,6-dinitro-4-trifluoromethylphenyl, O-trimethylsilyl derivatives, which are analyzed by gas chromatography with electron-capture detection. The method has been applied to the assay of catecholamines in rat brain extracts. One hour after an acute dose (150 mg/kg i.p.) of L-3,4-dihydroxyphenylalanine, the rat brain concentration of DA increased by 130% while the concentration of NE was unchanged.