Neurochemical applications of liquid chromatography with electrochemical detection

Differential effects of p-chlorophenylalanine on indoleamines in brainstem nuclei and spinal cord of rats. I. Biochemical and behavioral analysis

The involvement of endogenous serotonergic pathways in the mediation of antinociception has been indicated by electrophysiological, pharmacological and behavioral experiments. However, manipulation of the indole pathway, either by lesioning of raphe nuclei or drug intervention, often produces disparate results. In particular, serotonin (5-HT) synthesis inhibition with p-chlorophenylalanine (PCPA) has been reported to produce either hyperalgesia or analgesia, depending upon the type of pain measurement examined. In the present study, we sought to evaluate the effects of PCPA on (1) behavioral responses to noxious stimulation, and (2) levels of serotonin, tryptophan and 5-hydroxyindoleacetic acid (5-HIAA) in raphe nuclei (pallidus, obscurus, magnus and dorsalis) and spinal cord regions by HPLC with electrochemical detection. Treatment of rats with 400 or 600 mg/kg of PCPA for 3 consecutive days resulted in significant elevations in pain thresholds assessed by tail withdrawal from radiant heat as well as vocalization to electric shock of the tail. The effect of PCPA on vocalization threshold was particularly striking, for the majority of animals showed a nociceptive-specific attenuation of this response. Although the PCPA induced changes in indole content of the various raphe nuclei were not unequivocally dose-dependent, differential reductions of serotonin and 5-HIAA were clearly detected in the various raphe regions. Nuclei raphe pallidus and obscurus were depleted of 5-HT and 5-HIAA to the greatest extent, whereas levels detected in nuclei raphe magnus and dorsalis were reduced by 30-40% from control values. Metabolism of 5-HT and 5-HIAA appeared unaffected by PCPA in all regions examined except the dorsal portion of the spinal cord. These findings collectively suggest that the effects of PCPA are not uniform throughout the central nervous system and raise the possibility that discrepancies in the behavior literature may be attributed to drug-induced changes in some, but not all serotonergic pathways.

Converting-enzyme inhibition buffers the counter-regulatory response to acute administration of nicardipine

1. To investigate the interaction of angiotensin-converting-enzyme (ACE) inhibitor and calcium antagonist, we conducted a double-blind randomized, placebo-controlled crossover study of a new ACE inhibitor (CGS 14824 A, 20 mg) during intravenous administration (i.v.) of nicardipine in eight normotensive healthy subjects. Nicardipine was infused to give cumulative doses of 1.25, 3.75, and 8.75 mg after 10, 20 and 30 min. 2. ACE inhibition was demonstrated 24 h after the first CGS 14 824 A intake (61%). Three hours after the second dose this inhibition was more marked (98%). 3. I.v. nicardipine administration induced a significant and similar fall in systolic or diastolic blood pressure with and without ACE activity (-3/-6 vs -2/-8%), while tachycardia was significantly decreased by CGS 14 824 A (+14 vs +30%, P less than 0.02). The increase of plasma noradrenaline was also significantly blunted (+1.8 +/- 0.3 vs +3.1 +/- 0.7 pmol ml-1, P less than 0.05). 4. Active and total plasma renin increased at the end of nicardipine infusion in the presence or absence of ACE inhibition. Inactive renin did not increase after nicardipine infusion under placebo. It was higher 3 h after the second intake of CGS 14 824 A and then increased after nicardipine infusion. 5. The rise in plasma aldosterone during i.v. calcium antagonist infusion was diminished after ACE inhibition (126 +/- 39 vs 277 +/- 120 pmol l-1, P less than 0.02). 6. In conclusion, converting-enzyme inhibition buffers the rise in heart rate, plasma noradrenaline and plasma aldosterone induced by acute calcium blockade.

Monoaminergic responses to spinal trauma. Participation of serotonin in posttraumatic progression of neural damage

The monoamines norepinephrine (NE), dopamine (DA), and serotonin (5-HT) and their major metabolites were measured in the spinal cord of rabbits following laminectomy or impact injury to the thoracic cord. Samples were taken 30 minutes, 60 minutes, 4 hours, and 6 weeks after injury. Utilization ratios (metabolite/transmitter) were calculated from the data. Turnover rates for NE and DA were also calculated at 30 minutes using the alpha-methylparatyrosine method. Trauma resulted in rapid and sustained elevations in 5-HT concentration at and around the injury site. The catecholamines were depleted slightly at the injury site. Levels of 5-hydroxyindole-3-acetic acid were elevated at 30 minutes but fell to baseline by 4 hours, resulting in a decrease in the 5-HT utilization ratio. The utilization and turnover of NE was increased at the injury site, while DA function was not affected. The large short-term increase in 5-HT levels may have been due to extravasation of platelet 5-HT stores into spinal tissue, rather than due to changes in neuronal 5-HT metabolism. At 6 weeks after injury, each monoamine and metabolite appeared to accumulate in spinal cord tissue proximal to the insult. Distal to the injury, depleted amine stores displayed augmented utilization. The data are discussed in terms of a serotonergic hypothesis of the progression of neural damage after trauma, with the interaction of 5-HT with raphe-spinal nerve terminals as a principal event.

Direct determination of vanillylmandelic acid in human urine by reversed-phase HPLC

A reversed-phase HPLC method for the determination of epinephrine, norepinephrine, dopamine, and vanillylmandelic acid (VMA) has been developed. The concentration of VMA in the urine of hypertensive patients was measured by direct injection after centrifugation. The method is useful for the diagnosis of pheochromocytoma.

Simultaneous determination of catechols in thalamic slices with liquid chromatography/electrochemistry

A method was developed for the simultaneous determination of dopamine (DA), epinephrine (E), norepinephrine (NE), 3,4-dihydroxyphenylacetic acid (DOPAC) and 3-methoxy-4-hydroxyphenylglycol (MHPG), as well as L-3,4-dihydroxyphenylalanine (L-DOPA) with liquid chromatography (LC) using electrochemical (EC) detection. With a ODS column and a mobile phase consisting of a sodium acetate-citrate with heptasulfonic acid, this method was applied on simultaneous determination of catechols released from thalamic slices of ddY mouse. The pretreatment of the bathing medium required only centrifugation, and the supernatant was injected directly into the LCEC system. The high potassium stimulation of catecholaminergically innervated thalamic slices led to increase in the levels of DA, NE, DOPAC and MHPG, especially of NE, but not that of L-DOPA itself. In the present study, we designed to make simultaneous determination of catechols released from thalamic slices for estimation of the physiological status of catecholaminergic neuronal activity.

Determination of dopamine and its metabolites in small volumes of rat brain dialysates using small-bore liquid chromatography with electrochemical detection

A miniaturized liquid chromatographic system with electrochemical detection (LC-ED) was developed and applied to the analysis of dopamine and its metabolites in dialysate samples collected from the rat brain in vivo. An existing LC-ED system was down-scaled using a 1 mm I.D. small-bore column operated at a reduced flow-rate and with an injection volume of 1 microliter. With the small-bore system the limit of detection for dopamine of ca. 0.06 pg was almost 50 times less than with the conventional system, which represents a two-fold improvement in concentration sensitivity. Miniaturization was accomplished with negligible loss in resolution by using a conventional commercial amperometric detector with minor modifications. The results indicate that a number of useful advantages could be realized by the combination of this small-bore LC-ED system and the in vivo brain dialysis method.

The assay of 4-hydroxy-3-methoxymandelic acid in urine by HPLC with electrochemical detection using bonded-phase silica sorbents for rapid, simple and selective extraction

A method is reported for the determination of 4-hydroxy-3-methoxymandelic acid (HMMA) by HPLC with electrochemical detection. The preparation of sample prior to HPLC has been studied and an efficient and selective extraction procedure described. Bonded-phase silica extraction columns and a vacuum manifold were used for the simple and rapid processing of batches of urine samples. Combining a reverse-phase C18 and an anion exchange column ensures selective isolation of HMMA. This simplified greatly the subsequent chromatography. The method was combined into a simple scheme for the routine analysis of urine HMMA, catecholamines and 5-hydroxyindole-3-acetic acid. The HPLC was standardised such that a single mobile phase was used with minor modification for each of the assays.

Effects of sustained hyperprolactinemia induced by chronic treatment with domperidone on central dopaminergic systems in the rat

Chronic treatment with Domperidone (DOM) had no effect on basal prolactin (PRL) secretion or basal levels of Dopamine (DA) metabolites in basal hypothalamus and striatum as compared with the vehicle treated rats. Animals chronically treated with DOM did not present tolerance to a challenge dose of Haloperidol (HAL) and DOM either measuring PRL secretion or striatal DA metabolite levels. The PRL-induced increase in hypothalamic 3,4-dihydroxyphenylacetic acid (DOPAC) was reduced. These results were accompanied by no change at striatal DA receptors, a slight reduction in density-affinity at hypothalamic DA receptors but clear-cut modification in pituitary DA receptors with the appearance of a high affinity-low capacity binding sites. It can be surmised that sustained hyperprolactinemia may induce tolerance in hypothalamic Tuberoinfundibular (TIDA) neurons involved in the inhibitory control of PRL secretion and a change in the kinetic properties of pituitary DA receptors, but it does not consistently affect the activity of the nigro-striatal DA system.

Simultaneous determination of the pharmacokinetics and pharmacodynamics of chlorpromazine in the brain of mice

The direct correlation analyses between the distribution of chlorpromazine (pharmacokinetics) and the biochemical effects of the drug on monoamine metabolisms (pharmacodynamics) are reported. Both samples for quantitative determination of CPZ and of monoamine transmitters and metabolites were obtained by organic extraction procedures from the same sample. The determinations were carried out by high performance liquid chromatography with electrochemical detection. CPZ affected the concentrations of metabolites of noradrenaline, dopamine and 5-hydroxytryptamine, but not those of the monoamine transmitters themselves. However, simultaneous assay demonstrated differences in effects of the drug on the transmitter systems. The concentrations of HVA and DOPAC were increased over a wide range of intracerebral concentrations of the drug, but those of MOPEG, in the range of higher concentrations. On the other hand, CPZ did not reveal any correlations between the intracerebral concentrations of the drug and 5-HIAA. These results suggest that CPZ affected primarily the dopaminergic system rather than the serotonergic one in the early stage of its biochemical actions. The proposed procedure is demonstrated to be simple and useful as a new approach in biochemical pharmacology. The same procedure can be applicable for other centrally acting drugs.

Simultaneous determination of histamine and N tau-methylhistamine with high-performance liquid chromatography using electrochemical detection

We have developed a liquid chromatographic method which uses electrochemical detection for the simultaneous quantitation of histamine and N tau-methylhistamine in rat brain. The amines are derivatized with the water-soluble Bolton-Hunter reagent (sulfo B-H). Perchloric acid extracts of rat brains are chromatographed on a strong cation-exchange resin. The eluate is evaporated and allowed to react with sulfo B-H at pH 9.8 at room temperature. The derivatization is complete after 30 s vortexing. The derivatives are purified using a cellulose-phosphate fibrous cation exchanger. They are quantified with an electrochemical detector at a potential of 0.56 V after preoxidizing the sample at 0.47 V. The derivatives of histamine, N tau-methylhistamine, and N alpha-methylhistamine are completely separated without interfering peaks. Since no N alpha-methylhistamine was detected in rat brain it was used as an internal standard. The detection limits are 0.1 pmol of histamine and 0.2 pmol of N tau-methylhistamine. The precision of this method is high, with within-run and between-run coefficients of variation of 2-7% and linearity of 0.999. Both histamine and N tau-methylhistamine peak heights increased significantly and selectively after treatment with pargyline. Because of the high sensitivity, accuracy, and precision, the histamine and N tau-methylhistamine contents of single nuclei of the rat hypothalamus can be routinely quantified.

Alterations of beta-adrenoceptors subsequent to myocardial infarction

Elevations and reductions of the number of beta-adrenoceptor binding sites are dependent on the strength and the duration of receptor interaction with respective agonists. In the paper presented here, results obtained by the authors concerning biosynthesis, storage and release of catecholamines following experimentally induced infarction of the myocardium in rats are compared with those of other authors for other species. Principally, storage and release of noradrenaline from ischemic hearts do not differ with the mode of inducing tissue hypoxia (stopped-flow ischemia, coronary artery ligation, occlusion of the great cardiac vein), nor for various species (rat, dog, guinea-pig). Differences are, however, present in the results of several beta-adrenoceptor binding studies performed after experimental myocardial infarction. Following acute infarction, an increase in the number of beta-adrenoceptor binding sites is generally observed, which is explained on the basis of an externalization of receptors from the cytoplasm ot the sarcolemmal membrane. Results pertaining to 2-3 days after infarction are not uniform: in guinea-pig hearts a marked drop in the number of beta-adrenoceptors has been reported, a mild rise in the number has been detected in the left and right ventricle of rat hearts. These divergent observations could arise from the experimental protocol employed, for instance in the binding assay and in the pretreatment given to the hearts prior to assay.

Circulating and tissue catecholamines in rats with chronic neurogenic hypertension

To study the role of peripheral catecholamines in plasma and different tissues in neurogenic hypertension we measured directly blood pressure, maximum rate of left ventricular pressure rise (dp/dtmax) and heart rate through an aortic catheter 5 weeks after total sino-aortic baroreceptor deafferentation in male Sprague-Dawley rats. Blood samples were collected through the same catheter to determine plasma catecholamine concentrations. Blood pressure and dp/dtmax were significantly higher in neurogenic-hypertensive rats when compared with sham operated rats. Plasma noradrenaline concentrations and plasma adrenaline concentrations reached significantly higher levels in neurogenic-hypertensive rats. In the heart noradrenaline content was lower (when calculated per g wet weight) and in the adrenal medulla adrenaline content was higher in neurogenic-hypertensive rats, when compared with sham operated controls. A significant positive correlation was found between dp/dtmax and plasma noradrenaline concentrations. It is concluded that sino-aortic baroreceptor deafferentation produces a significant chronic hypertension, probably supported by elevated plasma catecholamine concentrations and enhanced synthesis and release of adrenaline from adrenal medulla.

A simplified liquid chromatography and electrochemical detection method for measurement of plasma noradrenaline

A simplified, sensitive, and reliable method for the determination of noradrenaline (NA) in plasma using high-performance liquid chromatography and electrochemical detection is described. Investigations on the stability of NA in plasma and whole blood have effected an improvement in the method for collection and extraction of NA from plasma. Recycling the mobile phase and the elimination of the addition of antioxidants during the alumina extraction has resulted in savings in the costs of reagents and assay preparation time while retaining a recovery rate of 60% and improving detector response. The sensitivity of the assay for NA was 20 pg/ml of plasma using carbon paste prepared in the laboratory.

Formation and metabolism of pungent principle of Capsicum fruits. XV. Microdetermination of capsaicin by high-performance liquid chromatography with electrochemical detection

A new, highly sensitive method for quantitative separation and determination of capsaicin and dihydrocapsaicin by high-performance liquid chromatography with electrochemical detection is elaborated. The method employs a Cosmosil 5Ph column eluted with 100 mM potassium dihydrogenphosphate containing 45% acetonitrile (pH 5.0) at a flow-rate of 1.0 ml/min, and an electrochemical detector (at a potential of +750 mV versus the Ag/AgCl electrode). The detection limits for both capsaicin and dihydrocapsaicin were 12 pg (39 fmol) at a signal-to-noise ratio of 3:1. By applying this method, the biological half-life of capsaicin in the rat was investigated.

Drug level monitoring: cardiovascular drugs

Methods for the determination of cardiovascular drugs in blood and plasma are critically reviewed with emphasis on gas and liquid chromatographic techniques. The importance of the various procedures is discussed, in particular sample work-up where the conditions for isolation and derivatization of the compounds are decisive for the accuracy and precision of the methods. Compared with other assay techniques chromatographic methods are generally to be preferred owing to their better selectivity. In the review the following groups are discussed: digitalis glycosides, antiarrhythmic agents, beta-adrenoceptor antagonists, vasodilating agents, antihypertensive compounds, and diuretics.

Determination of tyrosine, tryptophan and their metabolic derivatives by liquid chromatography-electrochemical detection: application to post mortem samples from patients with Parkinson's and Alzheimer's disease

A procedure is described for the rapid determination of the major indoles and catechols. Analysis with picogram detection limits was done by high-pressure liquid chromatography on a C18 reverse-phase column using electrochemical detection (LCEC). This method provides a comprehensive list of compounds which can be simultaneously determined in brain samples and for which there is no necessity of derivatization or pre-column purification. The regional distribution of 9 neurochemicals from rat brain and the levels of 10 neurochemicals from human brain are presented. DOPA, TYR, NE, MHPG, DOPAC, 5-HIAA, TRP, DA, HVA, 3-MT and 5-HT were detected in the caudate nucleus and putamen. The levels of neurochemicals from the caudate and putamen of a demented patient with Parkinson's disease were variably decreased; catechol and indole losses were greatest in the putamen. The levels of neurochemicals in the caudate and putamen of patients with Alzheimer's disease (SDAT) were also variably decreased; loss of NE was seen only in putamen and losses of DA, HVA and 5-HT were uniform across both caudate and putamen. The CSF of SDAT patients showed changes in NE only.

Sympathoadrenal dysfunction in rats with chronic neurogenic hypertension

Compared to sham-operated controls 5 weeks after surgery neurogenic hypertensive rats with sino-aortic baroreceptor deafferentation had higher blood pressure, higher plasma noradrenaline and adrenaline levels, lower heart noradrenaline concentrations, higher adrenomedullary adrenaline levels and increased cardiac intraventricular pressure (dp/dtmax).

Determination of gamma-aminobutyric and glutamic acids in rat brain by liquid chromatography with electrochemical detection

The determination of glutamic and gamma-aminobutyric acids in rat brain regions by derivatization with o-phthaldialdehyde-thiol, isocratic separation by liquid chromatography, and quantification by electrochemical detection provides a simple and precise method for assessing changes in glutamatergic and GABAergic neuronal systems. Gamma-aminobutyric acid was eluted in 30-35 minutes followed by a washout step with 90% methanol to remove all amino acid derivatives with longer retention times. Homoserine was used as an internal standard. Significant increases in gamma-aminobutyric acid content in nucleus accumbens and substantia nigra could be detected 20 minutes after injection of 400 mg/kg valproic acid.

Quantitative determination and regional distribution of pipecolic acid in rodent brain

A rapid and sensitive method for the quantitative determination of pipecolic acid (PA), one of the three cyclic secondary imino acids present in mammalian brain is described. The quantification and identification of PA are accomplished in rat and mouse brain using high performance liquid chromatography with electrochemical detection (LCEC) and nipecotic acid (NPA) as an internal standard. The cyclic imino acids are derivatized with 2,4-dinitrofluorobenzene (DNFB) to dinitrophenyl derivatives. The remaining time for LCEC analysis is less than 30 min and the limit of sensitivity is in the lower picomole range. The levels of PA found in rat and mouse brain are comparable to those reported using gas chromatography/mass spectrometry. The regional distribution of PA shows higher concentrations of PA in hypothalamus, pons-medulla oblongata and cerebellum. The present results demonstrate that LCEC is sensitive enough to determine endogenous levels of PA in mg amounts of rodent brain tissue. Due to its simplicity and rapidity, the technique represents an alternative to existing methods. This method can also be used for determination of PA in CSF, blood or urine of hyperpipecolic patients.

Rapid automated analysis of biogenic amines and their metabolites using reversed-phase high-performance liquid chromatography with electrochemical detection

A method is described for the rapid automated analysis of: dopamine and norepinephrine; the major dopamine metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid; and the indoles tryptophan, serotonin, and 5-hydroxyindoleacetic acid in less than 0.5 mg of brain tissue. Samples are deproteinized, injected directly onto a reversed-phase high-performance liquid chromatography column, and quantitated using an electrochemical detector with a glassy carbon electrode. High sample stability permits the use of an automatic sample injector at ambient temperatures. Depending upon the column particle size, sample run times are less than 7-12 min. Thus, over 50 duplicate samples can readily be measured in a single day with very little operator attention. The chromatographic system used also resolves epinephrine, and the catecholamine metabolites: 3-methoxytyramine, normetanephrine, and 3-methoxy-4-hydroxyphenylglycol; and with very little modification this assay also could be used to measure these compounds.

Determination of neuropeptides in discrete regions of the rat brain by high-performance liquid chromatography with electrochemical detection

High-performance liquid chromatography (HPLC) in combination with electrochemical detection (ED) is suitable for measuring accurately the levels of oxidizable neuropeptides in small samples of brain tissue. We have determined by HPLC-ED and a two-column-switching technique the levels of leucine- and methione-enkephalin in rat brain. By a sequential two-column HPLC-ED method we have also determined the levels of cholecystokinin tetrapeptide and octapeptide sulphate in various regions of the rat brain. The values found are in good agreement with those reported previously based on radioimmunoassay. We conclude that, due to its simplicity, HPLC-ED is an attractive alternative to existing methods for the determination of some neuropeptides in biological material.

Liquid chromatographic assay for CSF catecholamines using electrochemical detection

A liquid chromatographic assay for noradrenaline (NA), dopamine (DA), and 3,4-dihydroxyphenylacetic acid (DOPAC) in human and monkey cerebrospinal fluid (CSF) is described. The limits of sensitivity vary between 0.1-0.3 pmol/ml of each catechol. Within-day precision as indicated by mean coefficient of variation (CV) of five days varied between 8.0-14.8 for NA (3.0-0.1 pmol/ml), 6.9-27.4 for DA (6.0-0.1 pmol/ml), and 4.1-17.6 for DOPAC (30-1 pmol/ml). Between-day precision (CV) was estimated to be 12.3, 14.9 and 16.6 for 4 pmol/ml of NA, DA and DOPAC, respectively. The method was reproducible enough for reliable quantitation of CSF free NA and DOPAC levels at physiological concentrations while the sensitivity for DA was too low to measure the free amine in less than 3 ml of human lumbar CSF. After acid hydrolysis total (free + conjugated) DA can, however, be quantified in CSF. Ranges for CSF NA and DOPAC levels were 0.13-2.0 and 0.43-14.6 pmol/ml in normal volunteers (n = 72), 0.19-3.19 and 0.7-7.09 pmol/ml in untreated chronic schizophrenic patients (n = 52), and 1.1-3.2 and 9.8-22.7 pmol/ml in rhesus monkeys (n = 8), respectively.

Catecholamine measurements by high-performance liquid chromatography

The development of sensitive detectors has allowed the use of high-performance liquid chromatography (HPLC) for measurements of catecholamines in extracts of plasma, urine, and tissue samples. Separation of the catecholamines may be effected by reversed phase chromatography or cation-exchange chromatography and quantitation by electrochemical detection (EC) or by fluorometry coupled with postcolumn derivatization according to the trihydroxyindole (THI) method. EC has a somewhat lower sensitivity than the THI method for norepinephrine (NE) and epinephrine (E). The THI method is insensitive to dopamine (DA). Basal plasma E levels of 0.1 nM (20 pg/ml) or less may be measured in sample volumes of 1-2 ml with EC. Sensitivity and reproducibility of an assay is not necessarily a guarantee of accuracy. It is argued that new methods and modifications of old methods should be validated against accepted methodology. This is rarely the case. Cation exchange HPLC with EC has been adequately validated, but only one of the reversed phase methods has been compared with radioenzymatic methodology. HPLC has the advantages of economy, speed, and more stimulating laboratory work, as compared with radioenzymatic methodology.

Determination of 4-hydroxyanisole in serum using liquid chromatography with electrochemical detection

4-Hydroxyanisole (p-methoxyphenol) has been used in the treatment of malignant melanomas. A simple, sensitive, and specific, method for its determination by liquid chromatography with electrochemical detection (LCEC) is described. Vanillin (4-hydroxy-3-methoxybenzaldehyde) was used as an internal standard.

Formation of adrenaline in the iris-ciliary body from adrenalone diesters

Many diesters of adrenalone have high ocular sympathomimetic activity although adrenalone itself, even if delivered intraocularly, is practically inactive. Thus these diesters cannot be considered pro-drugs of adrenalone, since adrenalone is not a drug. The mechanism of action of these adrenalone derivatives was studied on the selected, potent diisovaleryl adrenalone. It was found that adrenaline is formed from the diester, but not from adrenalone. While the inactive adrenalone is also formed hydrolytically and found in every compartment of the eye, the active epinephrine (adrenaline) was found only in the iris-ciliary body, as a result of a reduction-hydrolytic steps sequence. Thus the adrenalone diesters represent a type of site-specific delivery system for epinephrine.

Liquid chromatographic determination of homovanillic acid, 5-hydroxyindoleacetic acid and probenecid levels in human cerebrospinal fluid during probenecid test

Homovanillic acid and 5-hydroxyindoleacetic acid, respectively the major metabolites of the central neurotransmitters dopamine and serotonin, are present in human lumbar cerebrospinal fluid, and their determination during the probenecid test is used to study brain monoamine abnormalities in man. We developed a high performance liquid chromatographic technique coupled with electrochemical detection which allows the simultaneous determination of homovanillic acid and 5-hydroxyindoleacetic acid on 10 microliter of human lumbar cerebrospinal fluid. Another liquid chromatographic technique coupled with ultra-violet detection was applied to the measurement of probenecid after injection of 10 microliter of native cerebrospinal fluid. The main advantages of these two techniques are their simplicity, sensitivity, rapidity (five cerebrospinal fluid samples are analysed within one hour) and their good day-to-day reproducibility . These methods were applied to probenecid tests performed in several neurological patients.

High-performance liquid chromatographic analysis of S-adenosylmethionine and its metabolites in rat tissues: interrelationship with changes in biogenic catechol levels following treatment with L-dopa

A method is described for the simultaneous analysis of S-adenosylmethionine (SAM) and its metabolites, S-adenosylhomocysteine (SAH) and decarboxylated S-adenosylmethionine along with the natural polyamines, putrescine, spermidine and spermine. The separation is obtained by a reversed-phase ion-pair liquid chromatographic procedure with gradient elution followed by dual detection. The UV absorbance at 254 nm is used for the analysis of SAM and of the SAM metabolites, whereas the polyamines and some major amino acids, e.g., methionine, tyrosine and tryptophan, are analyzed by fluorescence detection after UV-cell derivatization with o-phthalaldehyde. A separate ion-pair reversed-phase high-performance liquid chromatographic (HPLC) procedure using isocratic elution and electrochemical detection is employed to analyse in the same tissue extracts the catechols and 5-hydroxyindoles, 3,4-dihydroxyphenylalanine (DOPA), dopamine, norepinephrine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, 4-hydroxy-3- methoxyphenylalanine , tryptophan, 5-hydroxytryptophan, serotonin and 5- hydroxyindolacetic acid. The sample preparation for the two HPLC procedures requires only homogenization of the tissues in perchloric acid and centrifugation before injection onto the column. The two chromatographic procedures have been applied to study the interrelationship, in various tissues of rats, between the SAM and SAH levels and the biogenic catechols after different treatments with L-DOPA alone or in combination with alpha- monofluoromethyl -DOPA, a potent enzyme-activated irreversible inhibitor of aromatic L-amino acid decarboxylase.

Biogenic amines and DOPA in the central nervous system of decapod crustaceans

The biogenic amines serotonin (5-HT), dopamine (DA), noradrenaline (NA), octopamine (OA) and the amino acid dihydroxyphenylalanine (DOPA) were identified and measured in the brain and the eyestalks of five decapod crustacean species using high pressure liquid chromatography (HPLC) with electrochemical detection. The amounts fall within 0.01-1.1 micrograms/g or 0.17-60 pmoles, and OA is the dominating amine in most species. THe DOPA levels in many of the species varied considerably between different measurements. It is concluded that the biogenic amines and DOPA are ubiquitous in the central nervous system of decapod crustaceans and the presence of NA and DOPA increases the number of presumed neurotransmitter/modulator candidates in the crustacean nervous system.

A study of the parameters affecting flow gradient analysis of catecholamines, DOPA and DOPAC by ion pair liquid chromatography with electrochemical detection

A general method for the determination of norepinephrine, epinephrine, dopamine, 3,4-dihydroxyphenylalanine and 3,4-dihydroxyphenylacetic acid is described. It employs the generation of a flow gradient during the analysis by ion-pair reversed phase liquid chromatography. The method allows a reduction of the analysis time maintaining high resolution of the peaks close to the solvent front. The effect of the flow gradient on column efficiency, detector response and retention are evaluated. The application to specimens of amniotic fluid, urine, human plasma and rat brain tissue is shown.

An automated method for the determination of biogenic amines and their metabolites by high-performance liquid chromatography

An automated high-performance liquid chromatographic method has been developed that allows for the determination of a number of compounds related to catechol- and indoleamine metabolism. The compounds that can be measured include L-DOPA, dopamine, dihydroxyphenylacetic acid, homovanillic acid, 3-methoxytyramine, norepinephrine, 3-methoxy-4-hydroxyphenylglycol, dihydroxyphenylglycol, vanilmandelic acid, epinephrine, 5-hydroxytryptophan, serotonin, 5-hydroxyindoleacetic acid, and 5-hydroxytryptophol. Dihydroxybenzylamine is used as an internal standard. Although dihydroxyphenylglycol and vanilmandelic acid could be detected and quantified, they could not be separated from each other. The method is completely automated and is sensitive enough to detect amounts as low as 500 fmol. Up to 200 samples a week can be analyzed in the automated mode. Using this method, analyses of brain tissue can be accomplished with no need for a cleanup procedure. The value of this procedure lies in its ability to simultaneously determine various amines and metabolites from small tissue samples in the same animals and with automation to analyze a relatively large number of samples a day with little attention by a technician.

Rapid and simple determination of homovanillic acid in plasma using high performance liquid chromatography with electrochemical detection

A rapid, yet highly reliable, procedure for determination of homovanillic acid (HVA) in plasma is described. After precipitation of proteins with perchloric acid, separation of sample components is directly achieved with high performance liquid chromatography on a reversed-phase column (C8), followed by quantitation based on electrochemical detection. The sensitivity of this method is 0.5 pmol/injection. Detector response is linear from the limit of detection to at least 0.5 nmol/injection. The intra-assay coefficient of variation is 2.2% in the concentration range of 50-150 pmol/ml plasma. The inter-assay coefficient of variation is 6.3%, based on determinations on 30 working days. A comparison of the present method and a specific gas chromatographic-mass spectrometric assay showed good agreement between the two procedures. One chromatographic run requires less than 16 min. for plasma and 10 min. for a standard.

Determination of cholecystokinin tetrapeptide and cholecystokinin octapeptide sulfate in different rat brain regions by high-pressure liquid chromatography with electrochemical detection

A method for the determination of cholecystokinins in biological material, based on high-pressure liquid chromatography with direct electrochemical detection (HPLC-EC), is described. Using this method, the levels of cholecystokinin tetrapeptide and octapeptide sulfate in rat brain cortex, hippocampus, striatum, and brain stem were measured and found to be comparable to those reported using radioimmunoassay methods. We show that HPLC-EC is sensitive enough to accurately determine neuropeptides in brain tissue without prior derivatization and is therefore, due to its simplicity, an attractive alternative to existing methods.

Sensitive high-performance liquid chromatographic determination of catecholamines in rat brain using a laser fluorimetric detection system

A sensitive high-performance liquid chromatographic method for the determination of catecholamines in rat brains has been developed using a fluorescence detector equipped with a continuous wave laser as an excitation light source. A new pre-purification and derivatization method was established and confirmed to be useful for the determination of catecholamines in biological samples. This pre-treatment method was simple, reproducible and specific. About 1 mg of the rat brain tissue was enough to determine catecholamines levels. The levels of dopamine and norepinephrine in rat brain were 0.40 and 0.87 ng, respectively, which agree with the findings of other workers.

Measurement of 3-methoxy-4-hydroxyphenylglycol in human plasma with high-performance liquid chromatography using electrochemical detection

A new method utilizing high-performance liquid chromatography with electrochemical detection for the determination of unconjugated 3-methoxy-4-hydroxyphenylglycol, a major metabolite of norepinephrine, in human plasma is described. A novel internal standard, 3-ethoxy-4-hydroxyphenylglycol, was used to correct for variations in extraction efficiency and detector sensitivity. Separation of sample components was achieved isocratically in 20 min per sample in a reversed-phase system. Column temperature had to be carefully regulated. The sensitivity of the assay is suitable for clinical studies, with a limit of detection of 2 pmol/ml. Intra- and interassay precision was good, with observed coefficients of variation of 7.5 and 8.8%, respectively. Accuracy was tested by comparing the results of the present HPLC method to those found with a specific gas chromatographic-mass spectrometric assay. A satisfactory correlation of 0.96 was obtained, with no significant bias between the two methods.

A quantitative method for determination of 5,6-dihydroxyindole-2-carboxylic acid using high-pressure liquid chromatography with fluorometric detection

A method for the determination of the urinary melanocyte metabolite 5,6-dihydroxyindole-2-carboxylic acid is described. The catecholic indole is adsorbed onto alumina, chromatographed on a reverse-phase octadecyl silica column, and detected by fluorometry. The sensitivity of the method permits detection of 1 pmol injected.

Simultaneous determination of 3-methoxy-4-hydroxyphenylglycol, 5-hydroxyindoleacetic acid, and homovanillic acid in cerebrospinal fluid with high-performance liquid chromatography using electrochemical detection

An improved high-performance liquid chromatographic method with electrochemical detection (HPLC-EC) for the simultaneous determination of 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxyindoleacetic acid (5-HIAA), and homovanillic acid (HVA) in cerebrospinal fluid (CSF) of humans and nonhuman primates is described. Quantitation is based on the use of an internal standard, 5-fluoro-HVA. Sample preparation consists of mixing an aliquot of CSF with a solution of the internal standard followed by ultrafiltration. The precision of the method is high, with within-run and between-run coefficients of variation of 2-6% and less than 10%, respectively, in the concentration ranges of the metabolites encountered in human lumbar CSF. Accuracy was tested by comparing the present HPLC method with specific gas chromatographic-mass spectrometric (GS-MS) assays for MHPG and HVA and a GC-MS-validated HPLC assay for 5-HIAA: the correlations obtained were 0.968 for MHPG, 0.989 for 5-HIAA, and 0.999 for HVA, with no systematic bias between the methods. The use of ascorbate as a preserving agent for monoamine metabolites in CSF was not found to be necessary when proper care was exercised in sample handling and storage. The analysis of samples with up to 2% ascorbic acid was possible as well, but MHPG had to be assayed separately using an extraction procedure and an alternative internal standard, 3-ethoxy-4-hydroxyphenylglycol.

Direct determination of 4-hydroxy-3-methoxyphenylacetic (homovanillic) acid in urine by high-performance liquid chromatography with amperometric detection

The improvement of high-performance liquid chromatographic analysis with electrochemical detection for urinary homovanillic acid is described. The method permits the chromatographic resolution of authentic homovanillic acid from coeluting interfering compounds in human and nonhuman primate, and rat urine. The electrochemically derived results are compared with post-column derivatized fluorescence results, and quality-control checks necessary to maintain assay precision in automated analysis are described.

Determination of norepinephrine and its metabolites released from rat vas deferens using high-performance liquid chromatography with electrochemical detection

We designed a rapid, simple and sensitive method for the determination of norepinephrine (NE) and its metabolites by reversed-phase high-performance liquid chromatography (HPLC) with electrochemical detection. NE, 3,4-dihydroxymandelic acid (DOMA), and 3,4-dihydroxyphenylglycol (DOPEG) were adsorbed on alumina and eluted with 0.2 N HCl. From the remaining solution, normetanephrine and 3-methoxy-4-hydroxyphenylglycol (MOPEG) were extracted with ethyl acetate in the presence of both borate buffer and K2HPO4. Vanillylmandelic acid was extracted with ethyl acetate after acidification of the solution with concentrated HCl. The combined ethyl acetate phase was evaporated and the residue was dissolved in 0.1 N HCl. A 50 mu1 aliquot of each eluate or solution was injected onto the HPLC. Detection limits ranged from 300 pg to 1 ng per initial sample. We used this method to determine substances in the medium following incubation of the rat vas deferens. Approximately 110 and 80 ng/g/10 min of DOPEG and MOPEG, respectively, were present under normal conditions. The electrical stimulation of tissues from the rat vas deferens led to increases in the levels of NE, DOPEG, DOMA and MOPEG. Normetanephrine and vanillylmandelic acid were not detected in the medium. This is probably the first documentation of the endogenous levels of NE and all its metabolites in medium containing tissue of the sympathetic nervous system.

Simultaneous multiple electrode liquid chromatographic-electrochemical assay for catecholamines, indole-amines and metabolites in brain tissue

To enhance the selectivity of liquid chromatographic-electrochemical assays for biogenic amines and metabolites in brain tissue, multiple electrode transducers were investigated. Two configurations of dual working electrodes were examined: parallel-adjacent and series arrangements. Using the raw detector currents with each configuration, peak-height ratios from simultaneously generated chromatograms were calculated to assess the selectivity of the instrument for direct injections of brain tissue supernatant. Ratios were consistent with injections of standards. Nearly coeluting peaks such as norepinephrine and 3-methoxy-4-hydroxyphenylglycol were resolved by using dual detector electrodes in series; only the catecholamines were detected at the downstream electrode owing to their electrochemical reversibility. The scheme was applicable to the assay of norepinephrine, 3,4-dihydroxyphenylacetic acid, dopamine, homovanillic acid, serotonin, 5-hydroxytryptophan and 5-hydroxyindole-3-acetic acid in brain tissue in less than 15 min.