Mass fragmentographic determination of some acidic and alcoholic metabolites of biogenic amines in the rat brain

Pharmacodynamic profile of CQP 201-403, a novel 8 alpha-amino-ergoline

The profile of action in animals of CQP 201-403, a novel 8 alpha-amino-ergoline, is in most aspects that of a very potent dopaminomimetic, both as a prolactin secretion inhibitor, and at the levels of the CNS and the cardiovascular system. Qualitatively CQP 201-403 differs slightly from bromocriptine and apomorphine in its effects on the CNS (no influence on serotonin metabolism in the rat cortex; induction of masculine mounting behavior in rats) and the cardiovascular system of the dog (reflex tachycardia in response to a blood-pressure fall). In man the new compound proved to be highly active in lowering prolactin serum levels and be more potent than bromocriptine (Parlodel).

CY 208-243: a unique combination of atypical opioid antinociception and D1 dopaminomimetic properties

Here we describe the potent antinociceptive action of the indolophenanthridine, CY 208-243, which has high affinities to the dopamine D1 binding and the opioid sites as well as to the 5-HT1A site. The antinociceptive action was comparable to that of morphine in most, but not all models of nociception, nevertheless, basic differences exist in its overall profile. Antagonism of CY 208-243's antinociceptive action was only possible with either high doses of naloxone or not at all and no cross-tolerance with morphine in CY 208-243 tolerant rats occurred. The biochemical basis for dependence liability may be absent and no opioid activity was observed in cultured hippocampal cells. Physical dependence did not occur after programmed administration in the rhesus monkey, nor did CY 208-243 cause respiratory depression in the rat (rather a stimulation). Lack of generalization in fentanyl-trained rats strongly suggests that CY 208-243 lacks opioid-like subjective cues. The coexistence of D1 dopaminergic and atypical opioid agonist properties represents a unique pharmacodynamic combination which is not shared with any other analgesic, and may provide safe and innovative pain therapy.

Biochemical, behavioural, and endocrine effects of CK 204-933, a novel 8 beta-ergolene

CK 204-933 displaces [3H]dopamine and [3H]spiperone with high affinity from D-1 and D-2 recognition sites in membranes of calf caudate. Results from functional in vitro tests suggest that it is a partial agonist at D-1 receptors and an antagonist at D-2 receptors. These opposite effects at dopamine receptor subtypes are also expressed in vivo. For instance, in 6-hydroxydopamine lesioned rats, CK 204-933 induces contralateral rotations which are antagonised by SCH 23390 but not by sulpiride. On the other hand, CK 204-933 induces a long lasting increase of dopamine turnover in rat striatum and antagonises apomorphine-induced gnawing behaviour in rats. CK 204-933 increases prolactin serum levels in rats after subcutaneous administration, whereas after oral administration a moderate decrease of prolactin serum levels was seen. The latter effect is probably due to the formation of active metabolites. CK 204-933 exhibits also a high affinity to [3H]prazosin binding sites and antagonises serotonin-mediated stimulation of adenylate cyclase in rat hippocampus. On the other hand, CK 204-933 has no effect of only very weak effects on noradrenaline and serotonin release from rat cerebral cortex slices, which is consistent with its weak effects on noradrenaline- and serotonin-turnover in rat brain. Based on these properties it is suggested that CK 204-933 could be of therapeutic value in brain diseases associated with disturbances of monoaminergic neurotransmission.

5,5-Diphenylhydantoin antagonizes neurochemical and behavioral effects of p,p'-DDT but not of chlordecone

Rats were given 75 mg/kg of 5,5-diphenylhydantoin (phenytoin) or vehicle 30 min prior to 75 mg/kg of 1,1,1-trichloro-bis(p-chlorophenyl)ethane (p,p'-DDT) (p.o.) or chlordecone (i.p.) and tremor was measured 12 h later. Rats were then killed, and regional brain levels of biogenic amines and their acid metabolites and amino acids were determined. Pretreatment with phenytoin significantly attenuated the tremor produced by p,p'-DDT but enhanced that produced by chlordecone. p,p'-DDT had significant effects on the levels of aspartate, glutamate, 5-hydroxyindoleacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylglycol (MHPG), whereas chlordecone increased glycine, 5-HIAA, and MHPG levels. Pretreatment with phenytoin blocked p,p'-DDT-induced increases of aspartate in the brainstem and spinal cord, 5-HIAA in the hippocampus, and MHPG in the brainstem and hypothalamus. Phenytoin significantly enhanced chlordecone-induced increases of MHPG in the brainstem. These data indicate that organochlorine-induced increases in noradrenergic activity in the brainstem and spinal cord may be directly related to the tremorigenic effects of these chemicals.

Quantitation of total MHPG in the rat brain using a non enzymatic hydrolysis procedure. Effects of drugs

An acid-catalyzed procedure has been used to hydrolyze MHPG-sulfate in homogenates of rat brain. The samples (in 0.4 mol/L perchloric acid) are treated for 3 min. at 100 degrees C in a water bath and aliquots are injected into a reversed phase HPLC system. Detection is achieved fluorimetrically. The absolute detection limit for MHPG is 150 pg, which allows the reliable determination of either free or total MHPG in rat brain in concentrations down to 15 ng/g, using the described procedure. The concentration of total MHPG found in the brains of saline-treated rats are 101 +/- 21 ng/g (mean +/- S.D.) which is in a good accordance with the concentration value for the same samples obtained using a GC-MS method (115 +/- 19 ng/g). Rats treated with clonidine (300 micrograms/Kg, i.p.) or yohimbine (10 mg/Kg, i.p.) showed brain concentrations of total MHPG of 68 +/- 22 ng/g and 299 +/- 85 ng/g, respectively. The utility of this method for the analysis of brain regions or brain nuclei (e.g. locus coeruleus) is also shown.

Supernumerary locus coeruleus neurons as a determinant of inherited epilepsy in the convulsive mutant mouse quaking

In quaking mice (a genetic model of epilepsy with an increased number of noradrenergic neurons) bilateral electrolytic coagulation of locus coeruleus (LC) in adult mice inhibited the convulsions elicited by somatic stimulations while neonatal 6-hydroxydopamine (6-OHDA) treatment remained ineffective upon the convulsions. Biochemical effects of the two treatments differed only in the brainstem where electrolytic lesion decreased while 6-OHDA treatment increased noradrenaline (NA) and 3-methoxy 4-hydroxyphenylethyleneglycol (MHPG) levels. Our results suggest that supernumerary LC neurons mediate the convulsions of the mutants through an action presumably restricted to the brainstem.

Pharmacological profile of the abeorphine 201-678, a potent orally active and long lasting dopamine agonist

The central dopaminergic effects of an abeorphine derivative 201-678 were compared to those of apomorphine and bromocriptine in different model systems. After oral administration, this compound induced contralateral turning in rats with 6-hydroxydopamine induced nigral lesions and exhibited strong anti-akinetic properties in rats with 6-hydroxydopamine induced hypothalamic lesions. It decreased dopamine metabolism in striatum and cortex, but did not modify noradrenaline and serotonin metabolism in the rat brain. 201-678 counteracted the in vivo increase of tyrosine hydroxylase activity induced by gamma-butyrolactone. In vitro it stimulated DA-sensitive adenylate cyclase and inhibited acetylcholine release from rat striatal slices. This compound had high affinity for 3H-dopamine and 3H-clonidine binding sites. These results indicate that 201-678 is a potent, orally active dopamine agonist with a long duration of action. Furthermore it appears more selective than other dopaminergic drugs.

Neurochemical effects of DDT in rat brain in vivo

p,p'-DDT and related agents act to hold the sodium channel open once opened and this effect is believed to be responsible for neurological effects of tremor and hyperexcitability in vivo. There is a good correlation between DDT-induced tremor and an increase in the levels of the metabolites of norepinephrine (NE), serotonin (5HT) and, to a lesser extent, dopamine (DA) in the brain stem (BS), hypothalamus (HYP), striatum (STR), or hippocampus (HPC). DDT also increases levels of excitatory amino acids glutamate (GLU) and aspartate (ASP), but the effect occurs only in the brain stem. These effects are dose- and time-related. Pharmacological studies found that blockade of alpha 1-adrenergic receptors attenuate DDT-induced tremor, while blockade of serotonergic, cholinergic muscarinic, and dopaminergic receptors augment the toxicity of DDT. Tremor was almost completely blocked in rats pretreated with hydantoin, an anticonvulsant believed to block repetitive firing of nerves by interfering with the inactivation gate of the sodium channel. A similar antagonism was observed for permethrin, a Type I pyrethroid believed to have a mechanism of action very similar to that of DDT. However, hydantoin increased the tremorigenic effects of chlordecone, an organochlorine whose mechanism has not been linked to the sodium channel. These data are consistent with the hypothesis that the in vivo neurotoxicity of some organochlorine insecticides is related to their effects on the sodium channel.

Effects of p,p'-DDT on the rat brain concentrations of biogenic amine and amino acid neurotransmitters and their association with p,p'-DDT-induced tremor and hyperthermia

Male, Fischer strain 344 adult rats were given various doses (25-100 mg/kg) of p,p'-DDT by oral gavage, and levels of biogenic amines, their metabolites, and amino acid neurotransmitters, tremor activity, and rectal temperature were measured at several intervals (2, 5, 12, and 24 h) after dosing. Dose-related increases in rectal temperature and in tremor activity were observed at 50-100 mg/kg 12 h after dosing. Tremorigenic doses of DDT increased the 5-hydroxyindoleacetic acid (5-HIAA) level in hypothalamus, brainstem, and striatum, whereas doses of 75 and 100 mg/kg increased the 3-methoxy-4-hydroxyphenylglycol (MHPG) level in hypothalamus and brainstem and the 3,4-dihydroxyphenylacetic acid level in striatum. Six amino acids were assayed in the brainstem, hypothalamus, and striatum; aspartate and glutamate levels were increased only in brainstem at 25-100 mg/kg. No consistent changes in concentrations of taurine, glutamine, glycine, or gamma-aminobutyric acid were observed in any of the regions assayed. Time-related increases in rectal temperature were seen 2-12 h after dosing, and the presence of tremor was observed 5-12 h after dosing; for both the time of peak effect was at 12 h. The DDT-induced hyperthermia and tremor were associated with dose- and time-related increases in levels of 5-HIAA, MHPG, aspartate, and glutamate. It is suggested that an increase in the turnover rate of 5-hydroxytryptamine (5-HT) may be responsible for the DDT-induced hyperthermia, whereas increases in the metabolism of 5-HT and norepinephrine may be involved in the tremor.

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.

Effect of chlordecone (Kepone) on the rat brain concentration of 3-methoxy-4-hydroxyphenylglycol: evidence for a possible involvement of the norepinephrine system in chlordecone-induced tremor

3-Methoxy-4-hydroxyphenylglycol (MHPG) is the major metabolite of norepinephrine (NE) in the rat brain. A single injection of tremorigenic doses of chlordecone to adult male Fischer-344 rats resulted in significant increases in MHPG concentrations in hypothalamus, brain stem, cerebellum, and caudate nucleus. The increase in MHPG was accompanied by a decrease in NE in the hypothalamus, suggesting that chlordecone treatment caused an increase in the turnover of NE in the brain. There was a dose- and time-related correlation between the increases in the concentrations of MHPG in hypothalamus, brain stem, and cerebellum and tremor in rats. The increase in MHPG in hypothalamus and brain stem occurred as early as 1 hr postdosing; this preceded the earliest measurable sign of tremor and initial hypothermia. Whether the alterations in the brain NE system are involved in the expression of the tremor and the initial hypothermia induced by chlordecone or whether they are merely associated with these changes is not clear.

Spontaneous recovery from motor asymmetry in adult rats with 6-hydroxydopamine-induced partial lesions of the substantia nigra

Animals with 6-hydroxydopamine-induced partial unilateral lesions of the substantia nigra exhibit spontaneous recovery from motor asymmetry, a transitory increase in dopamine turnover and an increase in tyrosine hydroxylase activity in the denervated striatum. The recovery of function in these animals seems to be due to the compensatory increase in dopamine metabolism as well as due to the time-dependent increase in tyrosine hydroxylase resulting from either enzyme activation or following reinnervation of the denervated striatum by nigral efferents spared by the partial lesions.

Dopaminergic properties of mesulergine (CU 32-085) and its metabolites

Mesulergine, an 8-alpha-aminoergoline, is now proven to be of utility in the clinic as an antiparkinsonian drug. However, the molecule itself shows in vitro and in vivo antidopaminergic properties. Mesulergine is rapidly metabolized into several pharmacologically active DA agonists. The influence of mesulergine on central DA metabolism in rats is dependent on the route of drug administration. It was possible to determine the different metabolites of this drug in plasma as well as in rat striatum. A correlation between the actual present concentration of the parent drug and DAergic metabolites and the net action on striatal DA metabolism was found. It may be concluded that mesulergine itself lacks DAergic activity but occupies DA receptors and is very rapidly metabolized into potent DA agonists.

Acute administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) reduces dopamine and serotonin but accelerates norepinephrine metabolism in the rat brain. Effect of chronic pretreatment with MPTP

Acute administration of MPTP (a synthetic heroin substitute) at 10-30 mg/kg (s.c.) produced 'Straub tail' phenomena, piloerection and reduced pelvis elevation in rats. The same dose decreased the concentrations of dopamine metabolites and reduced the rate of dopamine synthesis in the striatum. MPTP also reduced the metabolism of serotonin but accelerated that of norepinephrine in their corresponding terminal areas. The effects on central monoamines probably were not due to an agonistic action of MPTP on dopaminergic and serotonergic receptors, since MPTP only exhibited micromolar affinity to the corresponding binding sites. Furthermore, MPTP failed to induce rotational behavior in animals with unilateral nigrostriatal lesions. Chronic treatment of rats with MPTP (10 mg/kg s.c., daily for 3 weeks) did not result in massive degenerative changes in the nigrostriatal system. Histochemical analysis showed intact dopaminergic neurons. Striatal dopamine levels only were reduced by 10%. Dopaminergic neurons in rats chronically treated with MPTP responded normally to a pharmacological stimulus increasing their transmitter synthesis. Chronic treatment did not affect their response to an acute injection of MPTP.

Norepinephrine metabolism in man using deuterium labelling: origin of 4-hydroxy-3-methoxymandelic acid

A double isotope labelling technique was used to simultaneously determine the in vivo turnover rates of 4-hydroxy-3-methoxyphenylglycol (HMPG) and 4-hydroxy-3-methoxymandelic acid (HMMA, VMA) and the rate of HMPG oxidation to HMMA. Six healthy men were given intravenous injections of [2H3]HMPG and [2H6]HMMA and their plasma and urine samples analysed by gas chromatography--mass spectrometry (GC/MS) for the protium and deuterium species. HMPG and HMMA production rates were calculated by isotope dilution. The rate of HMPG oxidation to HMMA was obtained from the fraction of [2H3]HMPG recovered as [2H3]HMMA. The results showed that the entire production of HMMA, 1.11 +/- 0.21 mumol/h (mean +/- SE), could be accounted for by oxidation of HMPG, 1.49 +/- 0.31 mumol/h. In another experiment designed to avoid expansion of the HMPG body pool, a tracer dose of [14C]HMPG was given to the same subjects. The levels of [14C]HMPG and [14C]HMMA were measured in urine after extraction and separation by thin layer chromatography. Urinary excretion of endogenous HMPG and HMMA was determined by GC/MS. The results showed that the endogenous HMMA fraction of the total HMPG and HMMA urinary excretion rate, 0.57 +/- 0.04, was the same as the fraction of [14C]HMPG oxidized to [14C]HMMA, 0.62 +/- 0.01. Thus, HMPG is the main intermediate in the metabolic conversion of norepinephrine and epinephrine to HMMA in man.

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.

Rat brain norepinephrine metabolism: substantial clearance through 3,4-dihydroxyphenylethyleneglycol formation

To assess whether the metabolic clearance of rat brain norepinephrine (NE) through 3,4-dihydroxyphenylethyleneglycol (DHPG) formation is quantitatively comparable or greater than through 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) production, we studied the accumulation rates of conjugated DHPG and MHPG following probenecid administration in whole brain as well as in several brain regions. Administration of increasing doses of probenecid (100-500 mg/kg, i.p.) 1.5 h before sacrifice produced a dose-dependent increase of conjugated DHPG and MHPG levels. The maximum increment of these conjugated metabolites occurred at a dose of 300 mg/kg or higher. During the first hour following probenecid administration (300 mg/kg, i.p.), rat brain conjugated DHPG and MHPG levels accumulated linearly at a rate of 646 and 319 pmol/g/h, respectively. With the probenecid technique, the estimated appearance rates of conjugated DHPG significantly exceeded those of conjugated MHPG in hypothalamus, midbrain, brainstem, hippocampus, and cerebral cortex. These results clearly indicate that under resting conditions, formation and efflux of conjugated DHPG is the major route of metabolic clearance of rat brain NE.

Further studies on 4-hydroxy-3-methoxyphenylglycol oxidation in humans: effect of pool expansion and stereochemistry

The in vivo oxidation of the norepinephrine metabolite 4-hydroxy-3-methoxyphenylglycol (HMPG) to 4-hydroxy-3-methoxymandelic acid was studied in man with two different doses of deuterium-labeled HMPG and a tracer dose of [14C]HMPG. HMPG oxidation appeared to be dose-dependent with an oxidation of 62-70% for doses below or equal to 2.2 mumol. With the use of a capillary column coated with an optically active phase (Chirasil-Val) and gas chromatography mass-spectrometry the human urinary excretions of the two stereoisomers of deuterium-labelled HMPG (free + conjugates) were found to be equal.

Determination of meta- and para-hydroxyphenylacetic acid levels in single caudate nuclei by selected metastable peak monitoring: a new sensitive gas chromatographic--mass spectrometric procedure

The levels of meta- and para-hydroxyphenylacetic acids in rat brain caudate nuclei have been determined by a new gas chromatography-mass spectrometric (GC-MS) procedure in which metastable transitions specific to the derivatized acids are observed. The method is more sensitive than previous procedures and allows determination of the acid concentrations using single caudate nuclei. The levels of the meta- and para-isomers were found to be 9.2 +/- 1.5 and 43 +/- 3.7 ng/g, respectively.

Behavioural and biochemical effects in the adult rat after prolonged postnatal administration of clozapine

Rats were administered 10 mg/kg SC of clozapine (C) or vehicle solution (S) daily from day 1 after birth until 20 days of age. At 60 days of age (40 days after the postnatal treatment with C or S was interrupted) the stereotyped behaviour and the effects on locomotor activity elicited by apomorphine in S- and C-pretreated rats were investigated. The intensity of stereotyped behaviour as well as the decrement in locomotion induced by apomorphine (0.5--1 mg/kg SC) were not influenced by chronic C administration during development. Finally, at 80 days of age (60 days after the postnatal treatment with C or S was interrupted) rats were subjected to a differential reinforcement of low rates schedule (DRL15s). The results indicate that the acquisition of the DRL task performance criterion (Rs/Rf less than or equal to 2.5) was significantly more rapid in S-pretreated rats than in C-pretreated ones. In parallel biochemical experiments, homovanillic acid (HVA) content was measured in striatum in rats at 60 days of age (40 days after the postnatal treatment with C or S was interrupted). The results indicate that even if an acute challenge dose of 10 mg/kg C shows a certain degree of tolerance a single dose of 20 mg/kg C is still able to increase striatal HVA concentration in chronic C-pretreated animals. These data indicate that early postnatal administration of a non-cataleptogenic neuroleptic, like C, induces, in the adult rat, behavioural and biochemical changes which significantly differ from those elicited by a cataleptogenic neuroleptic, like haloperidol.

Noradrenergic neurotransmission in the brain of a convulsive mutant mouse, differences between the cerebral cortex and the brain stem

The Quaking mouse is a genetically determined model of convulsive disorders. We investigated the modulation of noradrenergic neurotransmission through alpha 2-adrenoceptors in the occipital cortex and the brain stem of this mutant. The endogenous levels of noradrenaline were similar in the cerebral cortex of the Quaking mice and their corresponding controls, while a significant increase of endogenous noradrenaline was found in the brain stem of the mutants. The rate of disappearance of noradrenaline in the cerebral cortex and the brain stem after injection of FLA 63 was identical in control and Quaking mice. The calcium-dependent electrically evoked overflow of 3H-noradrenaline from slices of occipital cortex was inhibited by clonidine and enhanced by yohimbine in Quaking as well as in normal mice. The negative feed-back mechanism mediated by presynaptic alpha 2-adrenoceptors operates to a similar extent in both strains of mice. In contrast to the occipital cortex, in the brain stem, the amount of neurotransmitter released by electrical stimulation was significantly increased in Quaking mice when compared with controls. However, in the brain stem, the negative feed-back regulation of noradrenaline release operates to a similar extent in both strains of mice. When the endogenous levels of MOPEG were determined in the brain stem, they were found to be significantly higher in the Quaking mice when compared to the controls. The results suggest that an increase in noradrenergic neurotransmission in the brain stem, rather than in the cerebral cortex, could contribute to the behavioural abnormalities exhibited by the Quaking mice.

Norepinephrine metabolism in man using deuterium labeling: turnover 4-hydroxy-3-methoxymandelic acid

4-Hydroxy-3-methoxymandelic acid (HMMA; VMA) labeled with three deuterium atoms was used to study the turnover and fate of HMMA following intravenous injection. Five healthy men were given a pulse dose of 5.0 mumol of labeled HMMA. Plasma and urinary levels of both endogenous and labeled HMMA were subsequently followed by gas chromatography-mass spectrometry using selected ion detection. The kinetic parameters were determined both with and without compensation for the pool expansion caused by the injection of labeled HMMA. The urinary recovery of labeled HMMA was 85 +/- 10% (mean +/- SD). No conversion of HMMA to 4-hydroxy-3-methoxyphenyl glycol (HMPG) occurred. The biological half-life of HMMA was 0.54 +/- 0.22 h. The apparent volume of distribution was 0.36 +/- 0.11 L/kg. The production rate or body turnover was 1.27 +/- 0.51 mumol HMMA/h and urinary excretion rate was 0.82 +/- 0.22 mumol/h. These results show that HMMA is turnover over rapidly in a relatively small volume of distribution and that, unlike HMPG, it is an end metabolite of norepinephrine in man.

Mass fragmentographic determination of homovanillic acid in individual dopaminergic neuron systems of rat brain: application of reaction gas chromatography

Homovanillic acid (HVA) levels of 12 discrete rat brain areas were determined by a mass fragmentographic method using the reaction gas chromatographic technique. The use of reaction gas chromatography increased the sensitivity for determination of HVA. The sensitivity of this method allows measurement of HVA in small amounts of brain tissue. The HVA levels in polar, medial, and lateral fields of prefrontal cortex, anterior cingulate cortex, septum, amygdala, A12, A13, and A14 dopaminergic neurons were 0.417 +/- 0.018 ng/mg protein, 0.689 +/- 0.004, 0.753 +/- 0.024, 0.496 +/- 0.029, 1.311 +/- 0.046, 0.555 +/- 0.008, 1.949 +/- 0.077, 1.109 +/- 0.112, and 0.489 +/- 0.019, respectively. The HVA levels in these areas are first reported in the present paper.

A study on the acute effect of amphetamine on the urinary excretion of biogenic amines and metabolites in monkeys

1 The effects of an acute dose (3 mg/kg) of amphetamine on the urinary excretion of phenylethylamine (PEA), p-tyramine, their metabolites, catecholamine metabolites and p-hydroxymandelic acid, a major metabolite of p-octopamine were evaluated in the monkey. Amphetamine excretion was also measured. 2 Amphetamine was slowly eliminated from the body, being found in the urine at least six days after administration. 3 Amphetamine increased the excretion of PEA and decreased that of its major metabolite, phenylacetic acid (PAA). This pattern of changes is similar to that previously found in the urine of chronic schizophrenics. 4 The excretion of the dopamine metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC) was markedly reduced, that of vanilmandelic acid (VMA) remained unchanged while 3-methoxy-4-hydroxyphenylglycol (MHPG) was increased on the day of drug administration and persisted for at least a further six days. A similar extended effect on the excretion of p-hydroxymandelic acid (it was reduced) was also observed. 5 The excretion of p-tyramine but not its metabolite, p-hydroxyphenylacetic acid, was decreased by amphetamine during treatment and returned to normal levels six days later. 6 From the results obtained, it was concluded that amphetamine effects on behaviour cannot exclusively be attributed to its influence on catecholamines and that other biogenic amines may be involved. 7 Since PEA elicits many behavioural changes similar to those seen with amphetamine, and since amphetamine increases PEA excretion, we suggest that amphetamine may exert some of its behavioural responses through the release of PEA.

Estimation of the p and m isomers of hydroxyphenylacetic acid in mouse brain by a gas chromatographic procedure: their regional distribution and the effects of some drugs

The mouse brain contains 12.5 and 4.1 ng/g of p- and m-hydroxyphenylacetic acids, respectively. The hydroxyphenylacetic acids were isolated by chromatography on DEAE-Sephadex A-25 and quantitated as their pentafluoropropionyl and hexafluoropropanol esters by use of a gas chromatograph equipped with an electron-capture detector. The highest concentrations of p- or m-hydroxyphenylacetic acids were observed in the caudate nuclei (27.9 and 8.7 ng/g, respectively) and olfactory tubercles (20.2 and 5.3 ng/g, respectively). The identities of the p- and m-hydroxyphenylacetic acids were further confirmed as a consequence of the reductions observed following monoamine oxidase inhibition or the increases observed in the appropriate acid following the parenteral administration of p- or m-tyramine.

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

We have investigated the effects of 3, 4-dihydroxyphenylalanine (L-DOPA) and its deuterated analogue on the concentrations of alcoholic metabolites of catecholamines in rat brain by means of gas chromatography/mass spectrometry with selected-ion monitoring. Whole brain concentrations of the two neutral norepinephrine metabolites, 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) and 3, 4-dihydroxyphenylethyleneglycol (DHPG), were significantly increased in a dose-dependent manner by a single intraperitoneal injection of L-DOPA. Both MHPG and DHPG, as well as the corresponding dopamine metabolites, reached a maximum 1 h after injection. Brain MHPG and DHPG concentrations were elevated by 78 and 134%, respectively, 1 h after injection of 150 mg/kg L-DOPA. Analyses of discrete brain regions revealed that concentrations of the norepinephrine metabolites were elevated uniformly in all regions, except that MHPG showed a greater increase in the cerebellum than in other regions. The latter result appeared to be explained by the finding that 52% of the total MHPG in the cerebellum was unconjugated (compared to 15% in the whole brain). L-DOPA caused a proportionately greater increase in free MHPG than in total MHPG in the cerebellum and brain stem. By using deuterated L-DOPA in place of L-DOPA and measuring both the deuterated and nondeuterated norepinephrine metabolites, we demonstrated that virtually all of the increases in MHPG and DHPG were due to the conversion of the exogenous L-DOPA to norepinephrine. Thus, the effects of norepinephrine metabolism need to be considered in attempts to understand clinical and behavioral effects of L-DOPA.

Rat brain and plasma norepinephrine glycol metabolites determined by gas chromatography-mass fragmentography

A gas chromatographic-mass fragmentographic (GC-MF) procedure is described for the simultaneous quantitation of 3,4-dihydroxyphenylethyleneglycol (DHPG) and 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) in brain tissue and plasma. DHPG and MHPG were assayed as their respective acetyl-trifluoroacyl esters, using [2H2]DHPG and [2H3]MHPG as internal standards. Assay sensitives of at least 1 ng per sample were attainable for the quantitation of free glycols, whereas for determination of total DHPG, assay sensitivity was 2.5 ng. Whole rat brain total (99.2 +/- 4.11 ng/g) and free (13.0 +/- 1.14 ng/g) DHPG concentrations were similar to respective total (86.0 +/- 3.70 ng/g) and free (12.3 +/- 0.41 ng/g) MHPG levels. Total DHPG concentrations exceeded total MHPG levels in hypothalamus (3.0:1), midbrain (1.4:1), pons plus medulla (1.3:1), and hippocampus (1.5:1), whereas in other brain regions the levels of these metabolites were similar. In plasma, however, total DHPG levels were only 20% as high as MHPG concentrations. In mouse brain, DHPG and MHPG occurred almost entirely in free form (greater than 90%), but total DHPG levels were only 50% as high as respective MHPG concentrations. These results emphasize the substantial formation of DHPG compared with MHPG in rat and mouse brain and suggest that DHPG formation and efflux may be of equal or greater importance than MHPG in the metabolic clearance of CNS norepinephrine in some species.

Longitudinal urinary excretion of some "trace" acids in a human male

Conjugated and unconjugated urinary levels of phenylacetic acid (PAA), m-hydroxyphenylacetic acid (m-HPA) and p-hydroxyphenylacetic acid have been determined for 24-h urine samples obtained from a single healthy male over a 28-day period. Gas chromatographic--electron-capture and mass spectrometric--integrated ion current techniques incorporating appropriate internal standards were used. The average urinary excretion values obtained were (in mg/24 h): PAA unconjugated 0.67, conjugated 96.6; m-HPA unconjugated 7.3, conjugated less than 0.1; p-HPA unconjugated 22.4, conjugated less than 1.2. Following the ingestion of appropriate deuterated amino acid precursors the expected urinary deuterated trace acids were identified and quantitated; in the case of deuterated phenylethylamine, m-HPA and p-HPA as well PAA were identified and quantitated. This is the first evidence of phenylethylamine hydroxylation in the human. The longitudinal excretion of the trace acids was compared with that of the trace amines.

Specific and sensitive radioimmunoassay for 3-methoxy-4-hydroxyphenylethyleneglycol (MOPEG)

Antibodies that specifically bind the norepinephrine metabolite 3-methoxy-4-hydroxyphenylethyleneglycol (MOPEG) were produced in rabbits after injection of a derivative of MOPEG conjugated with bovine thyroglobulin. A sensitive radioimmunoassay was devised with this antiserum, in which as little as 0.5 nanogram of MOPEG can be accurately measured with a final antibody dilution of 1:180. The antibody appears to be specific for MOPEG, since tritiated MOPEG was not displaced from the antibodies by norepinephrine, epinephrine, dopamine, serotonin, or their major metabolites including MOPEG-sulfate (333 nanograms each).

Enduring behavioural and biochemical effects in the adult rat after prolonged postnatal administration of haloperidol

Rats were administered 0.5 mg/kg SC of haloperidol (H) or saline (S) daily from day 1 after birth until 20 days of age. At 60 days of age (40 days after the postnatal treatment with H or S was interrupted) the stereotyped behaviour and the effects on locomotor activity elicited by apomorphine in S- and H-pretreated rats were investigated. The intensity of apomorphine (0.5--1 mg/kg, SC)-induced stereotyped behaviour was significantly greater in the H-pretreated group than in S-pretreated animals and this was accompanied by a much more marked reduction of locomotor activity in H-pretreated than in S-pretreated rats. Finally, at 80 days of age (60 days after the postnatal treatment with H or S was interrupted) rats were subjected to a Differential Reinforcement of Low Rates schedule (DRL 15-s). The results indicate that the acquisition of the DRL task performance criterion (Rs/Rf less than or equal to 2.5) was significantly more rapid on S-pretreated rats than in H-pretreated ones. In parallel biochemical experiments, acute H produced smaller increases in dopamine turnover in chronic H-treated rats compared with S-treated controls. These data indicate that H treatment in neonatal rats induces behavioural and biochemical changes which can be observed up to 60 days after H withdrawal.

Identification and distribution of m- and p-hydroxyphenylacetic acids in the brain of the rat

The m and p isomers of hydroxyphenylacetic acid have been identified and quantitated in whole rat brain and in several regions using a capillary column high resolution gas chromatography - mass spectrometry procedure. Their concentrations were: for m-hydroxyphenylacetic acid (mean +/- S.E., number of determinations in parentheses)-whole brain, 2.3 +/- 0.3 ng/g (7); hypothalamus, 1.2 +/- 0.3 ng/g (5); caudate nucleus, 5.5 +/- 0.6 ng/g (5); brain stem, 1.8 +/- 0.1 ng/g (5); cerebellum, 1.2 +/- 0.1 ng/g (5) and the "rest," 1.7 +/- 0.1 ng/g (5); and for p-hydroxyphenylacetic acid-whole brain, 10.6 +/- 0.7 ng/g (7); hypothalamus, 4.5 +/- 0.1 ng/g (4); caudate nucleus, 28.3 +/- 1.6 ng/g (5); brain stem, 8.6 +/- 0.6 ng/g (5); cerebellum, 8.1 +/- 0.4 ng/g (5), and the "rest," 5.3 +/- 0.5 ng/g (5). This heterogeneous distribution parallels closely that exhibited by their respective precursor amines, m- and p-tyramine.

Drug-induced changes in the formation, storage and metabolism of tyramine in the mouse

1 The endogenous concentrations of p- and m-tyramine in the mouse striatum were determined by a mass spectrometric integrated ion current technique and concentrations were 21.3 and 6.1 ng/g, respectively.2 The present results further confirm that the administration of antipsychotic drugs (chlorpromazine, haloperidol, spiroperidol, alpha-flupenthixol and (+)-butaclamol) reduces p-tyramine concentrations in the mouse striatum. In contrast, striatal m-tyramine showed a tendency to increase, although only in the cases of haloperidol and (+)-butaclamol were the differences statistically significant.3 Administration of antipsychotic drugs to mice pretreated with tranylcypromine or clorgyline produced a significant reduction in striatal p-tyramine when compared with the concentrations obtained in mice given a monoamine oxidase inhibitor. These results suggest that antipsychotic drugs reduce striatal p-tyramine formation. The moderate increases produced by monoamine oxidase inhibitors on striatal m-tyramine were not significantly changed after the administration of an antipsychotic.4 Drugs that reduce dopamine turnover (apomorphine, piribedil, lergotrile, alpha-methyl-p-tyrosine) significantly increased the concentration of striatal p-tyramine. No significant changes were observed in striatal m-tyramine concentrations after apomorphine, piribedil or lergotrile; alpha-methyl-p-tyrosine produced a reduction in its concentration.5 Drugs that impair amine storage (reserpine, tetrabenazine, oxypertine) reduced striatal concentrations of p-tyramine. The m-tyramine concentrations were also reduced by reserpine or tetrabenazine.6 It is possible that striatal tyramines act as modulators, or transmitters, and control the activity of dopaminergic neurones.

An improved method for the differential assay of 3-O-methylated catecholamines in human urine using ion-pair extraction and gas chromatography electron capture detection

A gas chromatographic method is described for the quantitative determination of urinary normetadrenaline, metadrenaline and 3-methoxytyramine using electron capture detection. The N,O-dipentafluoropropionyl beta-O-ethyl derivatives of normetadrenaline and metadrenaline and the N,O-dipentafluoropropionyl derivative of 3-methoxytyramine were prepared. The amines were purified by ion exchange chromatography and ion pair extraction. Amine derivatives from urine extracts were identified definitively by mass fragmentography. The 24-h excretion value for normetadrenaline in human urine is 167 +/- 95 micrograms (mean +/- S.D.), for metadrenaline is 116 +/- 74 micrograms (mean +/- S.D.) and for 3-methoxytyramine is 82 +/- 68 micrograms (mean +/- S.D.).

The effect of acute and chronic desipramine and amitriptyline treatment on rat brain total 3methoxy-4-hydroxyphenylglycol

The effect of acute (single dose), short-term (4 days), and chronic treatment (21 days) with two tricyclic antidepressants desipramine and amitriptyline on brain 3-methoxy-4-hydroxyphenylglycol (MHPG) was examined in the rat. Amitriptyline had no effect on brain total MHPG irrespective of the duration of the treatment and did not interfere with the lowering effect of clonidine on brain total MHPG. Acute and short-term desipramine treatment decreased brain total MHPG in rats, while chronic desipramine treatment increased it. The differential effect of acute and chronic treatment of desipramine on the brain total MHPG was further demonstrated by the lack of interference with the lowering effect of clonidine on brain total MHPG by one single dose of desipramine; partial interference after 4 days and complete interference after 21 days of desipramine treatment.

CNS 3-methoxy-4-hydroxyphenylglycol: its peripheral assessment by isotopic dilution and theoretical significance

An isotope dilution model for the peripheral measurement of CNS catecholamine metabolism was examined in rabbits. 3H-norepinephrine (3H-norepinephrine (3H-NE) infusions were performed on rabbits before and after central sympathectomy via intraventricular 6-hydroxydopamine (6-OHDA) treatment. Urine samples were obtained 72 hr after 3H-NE infusion and analysed for specific activities (SAs) of 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3-methoxy-4-hydroxymandelic acid (VMA). The SA of MHPG was lower than that of VMA in all animals suggesting a source of unlabelled MHPG. The difference between the SAs of VMA and MHPG was abolished when the brain MHPG was markedly lowered by 6-OHDA injections. In animals which received 6-OHDA but retained moderate levels of brain MHPG, the difference between SAs of VMA and MHPG was maintained. The proposed model is able to predict and differentiate between rabbits that have severe depletion of CNS catecholamines and normal controls. The results suggest important relationships between CNS and peripheral NE metabolism and the compensatory capacity of the CNS to insult.