Estimation of the contribution of peripheral and central noradrenergic neurones to urinary 3-methoxy-4-hydroxyphenylglycol in the rat

Acute effects of neuroleptics on unmedicated schizophrenic patients and controls

Acute administration of haloperidol (0.2 mg/kg) produced many more side effects in normal controls than in unmedicated schizophrenic patients. Prior to the neuroleptic challenge, both groups were on the peripheral monoamine oxidase inhibitor, debrisoquin, for at least 1 week, in order to enhance the relative contribution of CNS catecholamine metabolites to those measured in both plasma and urine. The patient group had higher plasma levels of methoxyhydroxyphenylglycol (MHPG) and homovanillic acid (HVA) and higher urinary MHPG output than controls, but there were no effects of haloperidol challenge, compared to placebo challenge. In both groups there were significant declines in plasma HVA levels from 8:30 AM to 12 NOON. These declines were unaffected by the haloperidol challenge. Explanations for the marked differences in behavioral effects of haloperidol on patients and controls include the possibility that dopamine receptor numbers were increased in the brains of the schizophrenic patients.

A new approach to biochemical evaluation of brain dopamine metabolism

1. Dopaminergic neurotransmission in brain is receiving increased attention because of its known involvement in Parkinson's disease and new methods for the treatment of this disorder and because of hypotheses relating several psychiatric disorders to abnormalities in brain dopaminergic systems. 2. Chemical assessment of brain dopamine metabolism has been attempted by measuring levels of its major metabolite, homovanillic acid (HVA), in cerebrospinal fluid, plasma, or urine. Because HVA is derived in part from dopamine formed in noradrenergic neurons, plasma levels and urinary excretion rates of HVA do not adequately reflect solely metabolism of brain dopamine. 3. Using debrisoquin, the peripheral contributions of HVA to plasma or urinary HVA can be diminished, but the extent of residual HVA formation in noradrenergic neurons is unknown. By measuring the levels of methoxy-hydroxyphenylglycol (MHPG) in plasma or of urinary norepinephrine metabolites (total MHPG in monkeys; the sum of total MHPG and vanillyl mandelic acid (VMA) in humans) along with HVA, it is possible to estimate the degree of impairment by debrisoquin of HVA formation from noradrenergic neuronal dopamine and thereby better assess brain dopamine metabolism. 4. This method was applied to a monkey before and after destruction of the nigrostriatal pathway by the administration of MPTP.

Brief debrisoquin administration to assess central dopaminergic function in children

Central dopaminergic (DA) function in children was assessed by monitoring plasma-free homovanillic acid (pHVA) levels after brief (18 hour) administration with debrisoquin sulfate, a peripherally active antihypertensive agent that blocks peripheral, but not central, HVA production. Brief debrisoquin administration resulted in marked reductions in pHVA in each of six patients studied. In five of the six patients, post-debrisoquin pHVA levels remained relatively stable over the six-hour period of observation. No significant cardiovascular or behavioral side effects of debrisoquin were observed. The brief debrisoquin administration method appears to be a safe, simple, and potentially valid peripheral technique for evaluating aspects of central dopaminergic function in children with neuropsychiatric disorders. Additional work is needed to further establish this method's validity and reliability.

The effects of desipramine, zimelidine, electroconvulsive treatment and lithium on rat brain biogenic amines: a comparison with peripheral changes

The effects of 4 common treatments for affective disorders on total body norepinephrine (NE) and dopamine (DA) turnover and metabolism were evaluated in rats. The treatments were chronic desipramine (DMI), zimelidine (ZMI), electroconvulsion (ECT) and lithium (Li). The central effects of ECT and Li were also assessed in the brain. The results obtained were compared with the effects of these 4 treatments on total NE (Sum NE) and DA (Sum DA) turnover in depressed patients. We have also evaluated central and/or peripheral effects of these treatments on phenylethylamine, p-tyramine and serotonin metabolism. The urinary changes in Sum NE and DA observed after DMI, ZMI and Li in the rat were similar to those found in depressed patients; Sum NE was significantly reduced. In contrast to its effects on depressed patients, chronic ECT significantly increased Sum NE. Similar to depressed patients, ECT reduced the fraction of NE escaping re-uptake in the rat. Sum DA was not affected by DMI, ZMI or ECT, but was significantly reduced by chronic Li treatment. All 4 treatments significantly reduced serotonin metabolism as indicated by reduced 5-hydroxyindoleacetic acid excretion rates. DMI, ZMI and Li treatments significantly reduced phenylethylamine urinary but not p-tyramine urinary outputs. The opposite effect was observed after ECT. Consistent with their effects on Sum NE, Li reduced while ECT increased hypothalamic NE turnover as deduced from the changes in 3-methoxy-4-hydroxyphenylglycol's rate of formation. As for Sum DA, Li had no effect on 3,4-dihydroxyphenylacetic acid or homovanillic acid's rates of formation in the caudate nucleus. Chronic ECT produced a small, but significant increase in homovanillic acid's rate of formation in the caudate nucleus.

Assessment of central dopaminergic function using plasma-free homovanillic acid after debrisoquin administration

Central dopaminergic (DA) function in children and adults was assessed by monitoring plasma-free levels of the dopamine metabolite homovanillic acid (pHVA) before and after a single oral dose and chronic oral administration of debrisoquin. Debrisoquin inhibits peripheral metabolism of dopamine to HVA and does not cross the blood-brain barrier. By reducing peripheral formation of HVA through the use of debrisoquin, the remaining HVA in plasma more accurately reflects central DA activity. Debrisoquin administration resulted in marked reductions of pHVA in each of 12 patients studied. Eleven of the 12 subjects tolerated debrisoquin without physical or behavioral side effects. The debrisoquin administration method appears to be a safe and potentially valid technique for evaluating aspects of central dopaminergic function in children and adults.

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.

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

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

Mass fragmentographic analysis of monoamine metabolites in the spinal cord of rat after the administration of morphine

A mass fragmentographic method was used in which homovanillic acid (HVA), methoxyhydroxyphenylglycol (MHPG), and 5-hydroxyindoleacetic acid (5-HIAA) were measured from a single sample. The results describe the effect of morphine on the metabolism of the major monoamines, dopamine (DA), noradrenaline (NA), and 5-hydroxytryptamine (5-HT) in the spinal cord. Morphine has very little effect on the metabolism of DA and NA in the spinal cord. However, morphine causes a significant increase in the metabolism of spinal 5-HT. The increase in 5-HIAA induced by morphine is not restricted to the dorsal horn. The three main functional regions of the cord--dorsal horn (sensory), zona intermedia (autonomic), and ventral horn (somatic motor)--are affected to the same degree. The results indicate that morphine causes a generalized activation of serotonin neurons in the spinal cord. There appears to be little or no selectivity for those serotonergic neurons that innervate the dorsal horn. The results are discussed with reference to current data, which indicate a fairly strong link between descending serotonergic nerves and the mechanism of action of morphine-induced analgesia.

Plasma homovanillic acid as an index of brain dopamine metabolism: enhancement with debrisoquin

Plasma levels of the dopamine (DA) metabolite homovanillic acid (HVA) may be a useful measure of brain HVA production by central DA systems. Even though there is a significant peripheral contribution to plasma HVA, experimental manipulations that alter brain HVA produce parallel changes in plasma HVA levels. This study was designed to assess whether the ability of plasma HVA to reflect haloperidol induced increases in brain HVA could be strengthened by reducing the contribution to plasma HVA from peripheral sources. Debrisoquin sulfate, a monoamine oxidase inhibitor that does not enter the brain, was given in a low dose schedule to rats and lowered the peripheral contribution to plasma HVA by between 42 and 68%, resulting in a situation where between 62 and 87% of plasma HVA derived from brain. Using this dose schedule, rats pretreated with debrisoquin displayed a significant increase in plasma HVA following a lower dose of haloperidol than that required in the vehicle pretreated rats. In the debrisoquin pretreated group, a 71% increase in brain HVA was accompanied by a significant 60% increase in plasma HVA, whereas the vehicle pretreated group required a 136% increase in brain HVA to display a significant 50% increase in plasma. These findings indicate that debrisoquin pretreatment improves the reliability of plasma HVA to reflect changes in brain DA metabolism. Plasma HVA samples obtained from humans following debrisoquin may provide a clinically applicable method for assessing brain DA systems in neurologic and psychiatric illness.

Gas chromatographic method for the simultaneous determination of dopamine and norepinephrine metabolites

A new gas chromatographic method, using only flame ionization detection which can determine nanogram quantities of homovanillic acid, 3,4-dihydroxyphenylacetic acid, 3-methoxy-4-hydroxyphenylethyleneglycol and 3,4-dihydroxyphenylethyleneglycol in the same reaction, is described. These compounds are treated with diazoethane and n-butylboronic acid. Homovanillic acid and 3,4-dihydroxyphenylacetic acid are converted to their ethyl esters while 3-methoxy-4-hydroxyphenylethyleneglycol and 3,4-dihydroxyphenylethyleneglycol form cyclic boronates and are thus assayed. This method is quantitative, highly specific and sensitive. It has been applied to the analysis of these compounds in urine.

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.

Stereoselective excretion of (3-methoxy-4-sulphooxyphenyl)ethylene glycol (MHPG sulphate) in the dog

3-Methoxy-4-hydroxyphenylethylene glycol (MHPG) labelled with six deuterium atoms ([2H6]MHPG) was infused into two female greyhound dogs. Plasma and urine were analyzed for endogenous MHPG and [2H6]MHPG and their conjugates by the technique of selected ion monitoring gas chromatography-mass spectrometry. This analysis showed that the major forms of MHPG and [2H6]MHPG in the plasma and urine of the greyhounds were the sulphate conjugates. However, the plasma concentration of [2H6]MHPG sulphate increased continuously during the infusion period and the renal clearance of this compound was found to be much less than that of the endogenous sulphate. The explanation that his was due either to saturation of a renal transport mechanism or to a deuterium isotope effect was eliminated. Stereochemical analysis showed that, while the [2H6]MHPG used for infusion was a racemic mixture of two stereoisomers, much more of the nature(-)stereoisomer of [2H6]MHPG sulphate was excreted in the dog urine. It was also shown that both the (+) and (-)stereoisomers of [2H6]MHPG sulphate were sulphoconjugated at the 4-position of the aromatic ring.

The urinary excretion of 3-methoxy-4-hydroxyphenylglycól in acute myocardial infarction

Urinary excretion of 3-methoxy-4-hydroxyphenylglycol (MHPG), noradrenaline, adrenaline and vanillylmandelic acid (VMA) was studied in 30 patients with acute myocardial infarction. The excretion of MHPG was higher in patients with myocardial infarction than in the control group, with no difference between uncomplicated and complicated courses of the disease. The excretion of MHPG showed a negative although not significant correlation with noradrenaline and VMA during the first days of infarction and a statistically significant positive correlation on the 5th day of the disease. The possible causes of the changes observed are discussed.

Determination of 3-methoxy-4-hydroxyphenylglycol conjugates in urine. Application to the study of central noradrenaline metabolism in unmedicated chronic schizophrenic patients

On the basis of post-mortem studies it has been proposed that the central deficit in schizophrenia may be in noradrenergic transmission. It has also been proposed that there is a substantial central contribution to the excretion of the noradrenaline metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) and more particularly of its sulphate conjugate in man. There is throught to be a lesser central contribution to the excretion of the other major noradrenaline metabolites, vanillylmandelic acid (VMA) and the glucuronide conjugate of MHPG. A strong negative correlation was found between severity of illness in a group of 18 unmedicated chronic schizophrenic patients and their 24-h excretion of MHPG-sulphate but not of MHPG-glucuronide or VMA. However there was no significant difference in the mean excretion of MHPG conjugates or of VMA between the schizophrenic group and an institutional control group. This supports the idea of a relation between MHPG-sulphate excretion and central noradrenergic activity, but suggests that reduced brain noradrenaline turnover is neither necessary nor sufficient for schizophrenia to occur. One possible explanation is that reduced turnover pre-disposes towards a more severe illness in schizophrenics.

Dopamine beta-hydroxylase activity in brains of chronic schizophrenic patients

Postmorten brain specimens from nine chronic schizophrenic patients and nine control were assayed for activity of dopamine beta-hydroxylase, the enzyme responsible for the conversion of dopamine to norepinephrine. Unlike the results of previous reports, there was no statistically significant difference in enzyme activity between the patient and control groups. There were, however, significant negative correlations between dopamin beta-hydroxylase activity and the tim spent in the morgue before autopsy, and between enzyme activity of schizophrenics and dosage of chlorpromazine or its equivalent.