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B H Westerink

Publications and source records attributed to B H Westerink.

At least 145 records · Page 8Linked to original sources
PubMed1983

Amperometric detection of low concentrations of dopamine receptor agonists after liquid chromatographic on-column sample enrichment: effect of o-methylation on brain concentrations of dipropyl-5,6-ADTN and dipropyl-6,7-ADTN.

A sensitive and selective method of determination of N,N-dipropylamino-5, 6-dihydroxytetralin and its 6,7-dihydroxy isomer in rat plasma and brain tissue is described. The method is based on isolation of these dopamine receptor agonists from the biological samples on small Sephadex G-10 columns, followed by reversed phase high performance liquid chromatography with amperometric detection. Large volume (2 ml) injections result in on-column sample enrichment without a subsequent loss in column efficiency. Using this method the very low detection limit of 4 pmol/g was achieved in brain tissue. It was found that the lower in vivo potency as a centrally acting dopamine agonist of the 6,7-compared with the 5,6-isomer is almost entirely due to the lower brain concentrations achieved after peripheral administration of equimolar doses. This difference is mainly caused by different rates of O-methylation by catechol-O-methyltransferase, which follows from the fact that inhibition of this enzyme by tropolone leads to almost equal brain concentrations of the two isomers.

Animals↗
PubMed1983

On the significance of tyrosine for the synthesis and catabolism of dopamine in rat brain: evaluation by HPLC with electrochemical detection.

A chemical assay of tyrosine (Tyr) in nervous tissue is described. The method is based on a rapidly performed isolation of Tyr on small Sephadex G 10 columns, followed by reverse-phase HPLC in conjunction with amperometric detection. The method permitted the additional quantification of 3,4-dihydroxyphenylalanine, dopamine (DA), and its acidic metabolites. The method was applied to a study of the effects of gamma-butyrolactone, haloperidol, haloperidol in combination with amfonelic acid, morphine, NSD 1015, and tyrosine methylester on the concentration of Tyr in the striatum, frontal cortex, hypothalamus, and cerebellum of rat brain. The effect of tyrosine methylester on DA and its acidic metabolites was investigated in the striatum and frontal cortex. Morphine and NSD 1015 were found to increase Tyr levels. gamma-Butyrolactone, haloperidol, and haloperidol combined with amfonelic acid decreased the Tyr content in a manner related to their stimulatory effect on DA biosynthesis. These effects were restricted to DA-rich brain areas. It was concluded that during conditions of increased DA biosynthesis, the Tyr pool still possesses a considerable reserve capacity. The results bring into question the concept that brain Tyr is an important additional factor controlling catechol synthesis during increased tyrosine hydroxylase activity.

4-Butyrolactone↗
PubMed1982

Correlation between high-performance liquid chromatography and automated fluorimetric methods for the determination of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid and 5-hydroxyindoleacetic acid in nervous tissue and cerebrospinal fluid.

The correlation between automated fluorimetric methods and high-performance liquid chromatography is described for the determination of homovanillic acid and 5-hydroxyindoleacetic acid in cerebrospinal fluid, and for dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid in striata of rat brain. The automated fluorimetric methods for 3,4-dihydroxyphenylacetic acid and homovanillic acid showed a good correlation with the high-performance liquid chromatographic methodology. The fluorimetric determination for dopamine was somewhat less reliable than the high-performance liquid chromatographic assay. The fluorimetric assay for 5-hydroxyindoleacetic acid correlated poorly with the chromatographic method.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1982

Simultaneous determination of the formation rate of dopamine and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in various rat brain areas.

Administration of the MAO-inhibitor pargyline resulted in an increase of dopamine (DA) and an exponential decrease of the metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in various rat brain areas. From these curves the rate of formation of DA and the rate of removal of DOPAC were calculated, within one experiment, for the striatum, tuberculum olfactorium and frontal cortex. When the accumulation rate of 3-methoxytyramine was taken into account it appeared that the rate of DA formation was in good agreement with the rate of DOPAC removal in the brain areas studied. The contribution of the DA formation to the synthesis of noradrenaline in the frontal cortex appeared negligible. The earlier reported rapid rise of striatal DA levels after administration of aminotetralin-derived DA agonists suggests that the synthesis rate of the biogenic amine is higher than its rate of metabolism. It appeared from the present study that an increased rate of synthesis of DA induced by the DA agonists was responsible for this discrepancy.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1982

Reversed-phase liquid chromatography with amperometric detection of lipophilic dopamine analogues and determination of brain and serum concentrations after sample clean-up on small sephadex G-10 columns.

The liquid chromatographic determination of N-alkylated analogues of dopamine is described. The retention of these compounds, ranging from dopamine to N,N-dibutyl-dopamine, was studied on four bonded-phase columns, of which Nucleosil 5 C18 was chosen for routine use. The compounds were detected by a rotating disc amperometric detector. Samples of rat brain and serum were taken through a clean-up step on small Sephadex G-10 columns from which the dopamine analogues eluted in the same fraction as dopamine. The overall recovery was 70--90% from brain tissue and 60--70% from serum or plasma. The limit of detection for the catechol-containing compounds in tissue was 40--100 pg, for O-methylated ones 100--200 pg. The method is applied to the determination of dopamine analogues in rat brain after peripheral administration.

Animals↗
PubMed1982

Synthesis and pharmacological evaluation of conformationally restricted phenothiazine analogues.

The synthesis of 3-(dimethylamino)-2,3-dihydro-4-chloro-1H-pyrido[3,2,1-kl]phenothiazine, its 10-chloro analogue, and two chloro isomers of 2[(dimethylamino)methyl]-2,3-dihydro-1H-pyrido[3,2,1-kl]phenothiazine is described. In these compounds the side chain of chlorpromazine is fixed into a certain position in order to study the dopamine-overlap theory and the role of the substituents in the phenothiazine neuroleptics. The compounds were tested for their influence on dopamine metabolism, while for the second set their ability to displace [3H]spiroperidol from dopamine receptors was assessed. No neuroleptic activity was found from the pharmacological data. The results are discussed on the basis of conformational requirements for dopamine antagonistic activity.

Animals↗
PubMed1982

Effects of drugs interfering with dopamine and noradrenaline biosynthesis on the endogenous 3,4-dihydroxyphenylalanine levels in rat brain.

A chemical assay of 3,4-dihydroxyphenylalanine (DOPA) in nervous tissue is described. The method is based on a rapidly performed isolation of DOPA on small Sephadex G-10 columns, followed by reverse-phase HPLC with a trichloroacetic acid-containing eluent, in conjunction with a rotating disk electrochemical detector. The detection limit of the assay (about 100 pg/tissue sample) permits a detailed investigation of the regional distribution of endogenous DOPA levels in the rat brain. DOPA as well as dopamine (DA) could be quantified in the same chromatographic run. The assay was applied to a study of the effects of alpha-methyl-p-tyrosine, apomorphine, chlorpromazine, clonidine, gamma-butyrolactone, haloperidol, morphine, oxotremorine, pargyline, reserpine, and tyrosine methylester on the concentration of DOPA in the striatum, hypothalamus, frontal cortex, and cerebellum of the rat brain. Drugs known to interact with DA biosynthesis all caused characteristic changes of the DOPA content in the striatum and not in nondopaminergic brain areas. A close correlation existed between drug-induced changes in tyrosine hydroxylase activity and changes in the DOPA content in the striatum. Tyrosine methylester increased DOPA concentrations in all brain areas studied.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1982

Estimation of the turnover of 3-methoxytyramine in the rat striatum by HPLC with electrochemical detection: implications for the sequence in the cerebral metabolism of dopamine.

A highly sensitive method for the determination of 3-methoxytyramine (3-MT) in nervous tissue is described. The method is based on a rapidly performed isolation of 3-MT on small columns of Sephadex G 10, followed by reverse-phase high-performance liquid chromatography in conjunction with a rotating disk electrochemical detector. The detection limit of the assay (0.5-1 pmol/tissue sample) is about 10% of control value for microwave-killed rats. 3-MT as well as dopamine could be quantified in the same chromatographic run. Inhibition of catechol-O-methyl transferase with tropolone resulted in an exponential decline of 3-MT. From this exponential decline a turnover rate for 3-MT of 1.9 nmol/gh/h was calculated. In the same group of rats the turnover rate of homovanillic acid was 9.1 nmol/g/h. From these data it is concluded that in the rat striatum about 80% of homovanillic acid is formed from 3,4-dihydroxyphenylacetic acid and 20% from 3-MT.

Animals↗
PubMed1982

On the significance of endogenous 3-methoxytyramine for the effects of centrally acting drugs on dopamine release in the rat brain.

3-Methoxytyramine (3-MT) was measured in the striata of rats killed by microwave radiation. Apomorphine, gamma-butyrolactone (GBL), and reserpine decreased the 3-MT content. A slight but transient increase in 3-MT was observed after haloperidol. The turnover rate of 3-MT was unchanged 60 min after haloperidol treatment. (+)-Amphetamine induced a pronounced rise in the 3-MT content, which was potentiated after combined treatment with haloperidol. The increased 3-MT turnover rate that was observed after amphetamine treatment suggests that monoamine oxidase (MAO) inhibition is no explanation for the mechanism of interaction of this drug with dopamine (DA) metabolism. The central stimulants amphonelic acid and nomifensine increased 3-MT levels; no substantial change was seen after benztropine, morphine, or oxotremorine. It is concluded that a decreased release of DA is closely and rapidly reflected by decreased formation of 3-MT. 3-MT seems to be a much better indicator for decreased DA release than 3,4-dihydroxyphenylacetic acid or homovanillic acid.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1982

Use of alumina, sephadex G10, and ion-exchange columns to purify samples for determination of epinephrine, norepinephrine, dopamine, homovanillic acid, and 5-hydroxyindoleacetic acid in urine.

We investigated the usefulness of small Sephadex columns, prepared in Pasteur pipettes, in purifying samples to be analyzed for catecholamines, homovanillic acid, and 5-hydroxyindoleacetic acid. After free catecholamines in urine samples were purified on alumina followed by Sephadex G10, a reliable and simultaneous quantification of epinephrine, norepinephrine, and dopamine was achieved by using high-performance liquid-chromatography with electrochemical detection. Purification of urine on Bio-Rad prepacked ion-exchange columns followed by Sephadex G10 resulted in a reliable, fast (200 samples processed per week) method for determination of free catecholamines in urine. Analytical recoveries of both methods were between 80 and 95%, with a CV of about 3%. Single purification on Sephadex G10 sufficed to allow simultaneous determination of homovanillic acid and 5-hydroxyindoleacetic acid in urine. Analytical recovery for this method was about 90%, with a CV of about 5%. Sephadex G10 columns, which can be re-used without regeneration for at least one year, appear to have a great potential in clinical chemistry.

Chromatography↗
PubMed1981

Determination of picomole amounts of dopamine, noradrenaline, 3,4-dihydroxyphenylalanine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindolacetic acid in nervous tissue after one-step purification on Sephadex G-10, using high-performance liquid chromatography with a novel type of electrochemical detection.

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

3,4-Dihydroxyphenylacetic Acid↗
PubMed1980

Evaluation of the effect of drugs on dopamine metabolism in the rat superior cervical ganglion by HPLC with electrochemical detection.

Drugs known to affect central dopamine turnover, were investigated for their effects on dopamine metabolism in the rat superior cervical ganglion (SCG). A highly sensitive method (fmol range) for the determination of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) based on isolation on Sephadex columns in combination with high performance liquid chromatography (HPLC) with electrochemical detection, has been developed. The rate of formation of dopamine as well as of DOPAC was determined by monoamine oxidase inhibition. The calculated rate of formation for dopamine was: 250 pmol/ganglion/h, and for DOPAC: 289 pmol/ganglion/h. (+)-Amphetamine, apomorphine as well as haloperidol induced a decrease in DOPAC concentration in the SCG. The effect of haloperidol lasted for at least 8 h. The DOPAC concentrations indicated that chloral hydrate anesthesia markedly inhibited the activity of dopaminergic neurons in the SCG. These observations strongly suggest that the interaction between postsynaptic receptor blockade and the release of dopamine differs in the SCG and in central dopamine receptors.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1980

The significance of COMT activity in controlling dopamine agonist levels in brain and serum: studies with a prodrug and a metabolite of 6,7-ADTN.

After i.p. administration of the dibenzoylester of 2-amino-6,7-dihydroxytetralin (DB-6,7-ADTN) a metabolite was found in rat brain and serum, which was identified as 2-amino-6-hydroxy-7-methoxytetralin (7-O-MeADTN). By means of HPLC coupled with amperometric detection, time-concentration curves of 7-O-MeADTN in rat brain and serum were determined after 100 mumol/kg DB-6,7-ADTN. These showed a rapid formation and homogeneous distribution of high peak levels (4 nmol/g) of 7-O-MeATN. Brain and serum concentrations of 6,7-ADTN after 100 mumol/kg DB-6,7-ADTN, determined during catechol-O-methyltransferase (COMT) inhibition by tropolone, were 5--7 times higher than those during normal COMT activity, thus equalling 5,6-ADTN concentrations after 100 mumol/kg DB-5,6-ADTN. The greater susceptibility of 6,7-ADTN to metabolic degradation by COMT was confirmed by preliminary results of in vitro studies, which showed that two methoxy derivatives are formed from 6,7-ADTN and one, in very small amounts, from 5,6-ADTN. 7-O-MeADTN had no dopaminergic activity of its own, as after i.p. injection of 100 mumol/kg it was devoid of behavioural and biochemical effects typical for DA agonists. A homogeneous distribution and high peak concentrations (20 nmol/g after 15 min) were found in rat brain after this dose of the metabolite. The results indicate that a substantial amount of 6,7-ADTN, in contrast to 5,6-ADTN, is metabolized by COMT and that differences between brain concentrations of both isomers are almost exclusively due to differences in susceptibility for COMT. This has implications for the design of new DA agonists.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1980

Selective storage in vivo of 5,6-ADTN in dopamine-rich areas of the rat brain.

This study investigates the mechanism of the selective storage of the dopamine agonist 2-amino-5,6-dihydroxytetrahydronaphthalene (5,6-ADTN, used as the esterified prodrug) in densely innervated dopaminergic brain structures. The accumulation of 5,6-ADTN in dopamine-rich areas appeared to be non-saturable at the doses studied. In rats with a unilateral 6-OHDA lesion there was a corresponding unilateral decrease in 5,6-ADTN concentrations which suggests that the agonist interacts with dopamine uptake or storage mechanisms. Apart from an initial decreased penetration in the brain, reserpine-induced depletion of dopamine stores did not influence the accumulation of 5,6-ADTN in dopamine-rich areas, which suggests that 5,6-ADTN is taken up in the so-called 'non-reserpine sensitive DA-pool'. Unexpectedly, reserpine pretreatment caused a long-lasting (at least 170 h) decrease of 5,6-ADTN distribution in non-dopaminergic structures. 5,6-ADTN (used as the prodrug) could have a role to play in the elucidation of the significance of the various dopamine pools.

Animals↗
PubMed1980

Effect of non-catecholic 2-aminotetralin derivatives on dopamine metabolism in the rat striatum.

The concentrations of dopamine (DA), dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were measured in the striatum of rats after i.p. injection of dipropyl-2-aminotetralin and the four positional isomers of monohydroxy-dipropyl-2-aminotetralin. All compounds except 8-OH dipropylaminotetralin caused a decrease in DOPAC- and HVA-concentrations. In addition, 5-OH-dipropylaminotetralin produced a small elevation in DA concentrations. In contrast, 7-OH dipropylaminotetralin, in doses of 100 mumol/kg and more, decreased DA to 50% and initially increased HVA and DOPAC to about 200%, after which the concentrations of the metabolites fell to 30% or less. The 5-OH isomer was found to be the most potent compound, decreasing HVA concentrations to 70% at a dose of 0.14 mumol/kg. The potencies are compared to those of catechol-group containing DA-agonists such as apomorphine and N,N-dipropyl-5,6-dihydroxy-2-aminotetralin. In addition, a comparison is made with reported behavioural data. It is suggested that the more active N-alkylated 2-aminotetralins have a conformation which corresponds to that of the alpha rotamer of dopamine.

2-Naphthylamine↗