DOPA Levels Research Articles

Serotonin Levels in Attention Deficit Disorder

The relationship between blood serotonin, norepinephrine, dopa and lipid levels and the degree of hyperactivity, impulsiveness, inattention, and aggressiveness in 35 boys with ADHD, combined type, was studied at the Ness Ziona Mental Health Center, Nes Zona, Tel Aviv University, and other centers in Israel.

Circulatory levels of catecholamines, serotonin and lipids in attention deficit hyperactivity disorder.

Attention deficit hyperactivity disorder (ADHD) may be associated with a dysregulation of the catecholaminergic and serotonergic systems. Furthermore, ADHD is frequently complicated by aggressive impulsive behaviour, which is suggested to be related to low serum cholesterol levels. We examined the relationship between blood serotonin, norepinephrine, dopa and lipid levels and the degree of hyperactivity, impulsiveness, lack of concentration, and aggressiveness in boys with ADHD of low and high severity as determined by a specially designed formulated scale based on the DSM-IV criteria for ADHD. No differences were noted between the groups in any of the peripheral biological parameters except blood serotonin, for which a tendency (P=0.08) towards lower levels was observed in the children with more severe disorder. We conclude that children with severe ADHD may have a different serotonin turnover compared to children with mild ADHD. These results may have implications for our understanding of the pathogenesis of ADHD, at least the more severe type.

The decisive step in betaxanthin biosynthesis is a spontaneous reaction1

Experiments were performed to confirm that the aldimine bond formation is a spontaneous reaction, because attempts to find an enzyme catalyzing the last decisive step in betaxanthin biosynthesis, the aldimine formation, failed. Feeding different amino acids to betalain-forming hairy root cultures of yellow beet (Beta vulgaris L. subsp. vulgaris "Golden Beet") showed that all amino acids (S- and R-forms) led to the corresponding betaxanthins. We observed neither an amino acid specificity nor a stereoselectivity in this process. In addition, increasing the endogenous phenylalanine (Phe) level by feeding the Phe ammonia-lyase inhibitor 2-aminoindan 2-phosphonic acid yielded the Phe-derived betaxanthin. Feeding amino acids or 2-aminoindan 2-phosphonic acid to hypocotyls of fodder beet (B. vulgaris L. subsp. vulgaris "Altamo") plants led to the same results. Furthermore, feeding cyclo-3-(3,4-dihydroxyphenyl)-alanine (cyclo-Dopa) to these hypocotyls resulted in betanidin formation, indicating that the decisive step in betacyanin formation proceeds spontaneously. Finally, feeding betalamic acid to broad bean (Vicia faba L.) seedlings, which are known to accumulate high levels of Dopa but do not synthesize betaxanthins, resulted in the formation of dopaxanthin. These results indicate that the condensation of betalamic acid with amino acids (possibly including cyclo-Dopa or amines) in planta is a spontaneous, not an enzyme-catalyzed reaction.

Increased site-specific phosphorylation of tyrosine hydroxylase accompanies stimulation of enzymatic activity induced by cessation of dopamine neuronal activity.

Activation of striatal dopamine (DA) neurons by neuroleptic treatment or by electrical stimulation of the nigrostriatal pathway increases the activity of tyrosine hydroxylase (TH). The increase is mediated by phosphorylation of the enzyme. However, abolition of DA neuronal activity [by gamma-butyrolactone (GBL) treatment or transection of the nigrostriatal pathway] also increases TH activity. Quantitative blot immunolabeling experiments using site- and phosphorylation state-specific antibodies to TH demonstrated that GBL treatment (750 mg/kg, 35 min) significantly increased phosphorylation at Ser19 (+40%) and Ser40 (+217%) without altering Ser31 phosphorylation. Concomitantly, GBL treatment [along with the 3,4-dihydroxyphenylalanine (dopa) decarboxylase inhibitor NSD-1015, 100 mg/kg, 30 min] increased in vivo striatal dopa accumulation and in vitro TH activity 3-fold. Likewise, cerebral hemitransection of the nigrostriatal pathway significantly increased phosphorylation of TH at Ser19 (+89%) and Ser40 (+158%) but not at Ser31; dopa levels were increased accordingly (+191%). Kinetic analysis of TH activity established that GBL treatment and hemitransection primarily decreased the Km for the cofactor tetrahydrobiopterin (3-fold). The effects of GBL and hemitransection were abolished or attenuated by pretreatment with the DA agonist R-(-)-N-n-propylnorapomorphine (NPA; 30 microgram/kg, 40 min), presumably via stimulation of inhibitory presynaptic DA autoreceptors. NPA dose-response curves for reversal of GBL-induced dopa accumulation and Ser40 phosphorylation were identical; however, only the highest dose of NPA reversed the small and variable increase in Ser19 phosphorylation. Thus, TH activity seems to be regulated by phosphorylation in both hyper- and hypoactive striatal DA neurons; in the latter case, activation seems to be caused by selective phosphorylation of Ser40.

In vivo intrinsic efficacy of the 5-HT 1A receptor antagonists NAD-299, WAY-100,635 and ( S)-(-)-UH-301 at rat brain monoamine receptors

The receptor-mediated control of brain monoamine synthesis was used to examine the in vivo intrinsic efficacy of the 5-HT 1A receptor antagonists NAD-299, S(-)-UH-301 and WAY-100,635. The rate of monoamine synthesis was estimated by measuring the accumulation of DOPA and 5-HTP in the ventral neostriatum and the ventral hippocampus in rats pretreated with an inhibitor of cerebral aromatic L-amino acid decarboxylase. S(-)-UH-301 (2.0–32.0 μmol kg −1), but not WAY-100,635 (0.08–1.2 μmol kg −1), produced a decreased 5-HTP accumulation in the neostriatum and in the hippocampus. The administration of NAD-299 (0.75–12.0 μmol kg −1) resulted in a slight increase in neostriatal, but not hippocampal, 5-HTP acccumulation. Neostriatal DOPA accumulation was decreased by S(-)-UH-301, whereas treatment with WAY-100,635 resulted in an increase. NAD-299 did not affect neostriatal DOPA levels. There were no effects by any of these agents on DOPA levels in the ventral hippocampus. It is concluded that S(-)-UH-301, but not WAY-100,635 or NAD-299, displays intrinsic efficacy at brain 5-HT 1A and DA D 2/3 receptors, whereas WAY-100,635 behaves as a DA D 2/3 receptor antagonist. By this comparison, NAD-299 appears to be the most selective and specific 5-HT 1A receptor antagonist.

Role of dopamine in the peripheral mechanisms of respiration control

Under clinical conditions, we studied the interaction between dopamine (DA) metabolism and hypoxia stimulationrelated ventilatory responses (HVR) before and after adaptation to periodical hypoxic episodes. Thirty-seven young and elder persons were tested; among elder tested subjects there were patients with Parkinson’s desease treated or not treated with DOPA-DA precursor-containing drugs (levoDOPA/carbiDOPA). We measured the HVR indices and DA and DOPA contents in the venous blood of tested persons before and after a 14-day-long hypoxic training. The highest indices of the ventilation sensitivity to hypoxia together with the lowest above-mentioned chemical indices were observed in young persons. An increase in the DA and DOPA levels in the venous blood were observed concurrently with suppression of the ventilation responses to hypoxic episodes. After a course of periodical hypoxic sessions, we observed in all groups opposite dynamics of DA and DOPA metabolism. An increase in the DA level in young persons and a trend toward its decrease in older healthy persons and parkinsonian patients was nevertheles accompanied by an HVR increase in all groups. Possible relations between the DA metabolism indices and peripheral mechanisms of respiratory control are discussed.

Differential effects of chemical sympathectomy on expression and activity of tyrosine hydroxylase and levels of catecholamines and DOPA in peripheral tissues of rats.

Tyrosine hydroxylase (TH) mRNA and activity and concentrations of 3,4-dihydroxyphenylalanine (DOPA) and catecholamines were examined as markers of sympathetic innervation and catecholamine synthesis in peripheral tissues of sympathectomized and intact rats. Chemical sympathectomy with 6-hydroxydopamine (6-OHDA) markedly decreased norepinephrine and to a generally lesser extent TH activities and dopamine in most peripheral tissues (stomach, lung, testis, duodenum, pancreas, salivary gland, spleen, heart, kidney, thymus). Superior cervical ganglia, adrenals and descending aorta were unaffected and vas deferens showed a large 92% decrease in norepinephrine, but only a small 38% decrease in TH activity after 6-OHDA. Presence of chromaffin cells or neuronal cell bodies in these latter tissues, indicated by consistent expression of TH mRNA, explained the relative resistance of these tissues to 6-OHDA. Stomach also showed consistent expression of TH mRNA before, but not after 6-OHDA, suggesting that catecholamine synthesizing cells in gastric tissue are sensitive to the toxic effects of 6-OHDA. Tissue concentrations of DOPA were mainly unaffected by 6-OHDA, indicating that much of the DOPA in peripheral tissues is synthesized independently of local TH or sympathetic innervation. The differential effects of chemical sympathectomy on tissue catecholamines, DOPA, TH mRNA and TH activity demonstrate that these variables are not simple markers of sympathetic innervation or catecholamine synthesis. Other factors, including presence of neuronal cell bodies, parenchymal chromaffin cells, non-neuronal sites of catecholamine synthesis and alternative sources of tissue DOPA, must also be considered when tissue catecholamines, DOPA and TH are examined as markers of sympathetic innervation and local catecholamine synthesis.

Increased Plasma Atrial Natriuretic Factor in Catecholamine-Producing Tumor Patients

The aim of this study was to evaluate plasma levels of ANF in patients with catecholamine-secreting tumors with and without hypertension and to relate ANF secretion to levels of plasma and urinary catecholamines and blood pressure. Twenty-one pheochromocytoma (15 with sustained, 6 with paroxysmal hypertension), 6 neuroblastoma (1 hypertensive) patients and 28 aged-matched controls were studied in basal conditions. Plasma and urinary norepinephrine (NE),epinephrine (E), dopamine (DA) and DOPA were determined by HPLC-ED and plasma ANF by RIA. Both neuroblastoma and pheochromocytoma patients had significantly higher plasma ANF levels than controls. Neuroblastomas showed higher ANF concentration than pheochromocytomas. No differences were found in plasma ANF between hypertensive and normotensive patients. Pheochromocytomas with ANF levels within the normal range had plasma and urinary NE and urinary DA and DOPA levels significantly higher than patients with

Pallidotomy improves motor responses and widens the levodopa therapeutic window in Parkinson's disease.

Stereotactic posteroventral pallidotomy (PVP) as a treatment for Parkinson's disease (PD) symptoms has been increasingly used in moderate-advanced disease. We examined the pharmacodynamic responses of PD patients to single oral levodopa doses and intravenous levodopa infusions before and after PVP surgery. Nine subjects with advanced PD received a single oral dose and ramped intravenous levodopa infusions before and 3-5 weeks after unilateral PVP. Timed motor tasks, Unified Parkinson's Disease Rating Scale (UPDRS) evaluations, and ordinal dyskinesia rating were performed after oral levodopa and during i.v. levodopa infusions. Serum prolactin and dopa levels were measured during the levodopa infusions. Overall timed motor but not motor UPDRS scores were improved after PVP in both the worst ("off") and best ("on") states. Contralateral but not ipsilateral limb dyskinesias were substantially reduced at all serum (dopa) levels after PVP. Ipsilateral and contralateral timed motor performance at low serum (dopa) levels was improved by PVP. Walking speeds at all serum (dopa) levels were not changed by PVP. Serum prolactin was reduced equally by increasing (dopa) preoperatively and postoperatively. PVP significantly and favorably altered oral and intravenous levodopa pharmacodynamics by improving bilateral limb motor function and contralateral dyskinesia but did not alter walking speed. PVP appears to widen significantly the therapeutic window for levodopa in PD.

Monoaminergic effects of high-dose corticotropin in corticotropin-responsive pediatric opsoclonus-myoclonus.

Children with the opsoclonus-myoclonus syndrome (OMS) usually respond to corticotropin (adrenocorticotrophic hormone, ACTH) treatment but the mechanism of benefit is unknown. We previously showed that both cerebrospinal fluid (CSF) homovanillic acid (HVA) and 5-hydroxyindole-acetic acid (5-HIAA) concentrations are low in pediatric OMS. In this study, we measured levels of CSF Dopa, catecholamines, deaminated metabolites of catecholamines, as well as HVA and 5-HIAA in eight patients before and during treatment with ACTH. All the children were ACTH-responsive with 50-70% improvement in multiple clinical features of OMS. ACTH treatment reduced the HVA concentration in every child by a mean of 21% (p < 0.001). Treatment with ACTH was associated with significant correlations between dopaminergic markers such as HVA, dihydroxyphenylacetic acid (DOPAC), and Dopa. There were no significant changes in the CSF concentrations of the noradrenergic markers norepinephrine (NE) and dihydroxyphenylglycol (DHPG), or the serotonergic marker 5-HIAA. The only child with a marked inflammatory pattern in CSF, which was reversed by ACTH, was atypical for a large increase in NE and decrease in 5-HIAA during ACTH treatment. Beneficial effects of ACTH in OMS are not associated with normalization of HVA or 5-HIAA levels. The pattern of decreased HVA and unchanged DOPAC levels could reflect decreased extraneuronal uptake of catecholamines (which steroids inhibit) or decreased 0-methylation of catecholamines in nonneuronal cells.

Reduced striatal tyrosine hydroxylase activity is not accompanied by change in responsiveness of dopaminergic receptors following chronic treatment with deprenyl

Deprenyl is the only selective monoamine oxidase B (MAO-B) inhibitor that is in clinical use for the treatment of Parkinson's disease. Our previous studies showed that chronic treatment of rats with low (MAO-B selective) doses of deprenyl inhibited dopamine (DA) re-uptake and enhanced DA release in the striatum. These changes could affect DA synthesis rate by activation of negative feedback loops. Chronic deprenyl treatment has also been suggested to cause down-regulation of release-modulating DA receptors. The effects of chronic and acute treatment with deprenyl on ex vivo striatal tyrosine hydroxylase activity were therefore studied, by determination of steady-state tissue level of DOPA following administration of NSD-1015 (100 mg/kg i.p.). In addition, we assessed changes in the in vivo sensitivity of dopaminergic receptors from the reduction in DOPA extracellular level after systemic apomorphine administration (2.5 mg/kg s.c.), following elevation of microdialysate DOPA by systemic or local aromatic amino acid decarboxylase inhibition with NSD-1015. Chronic treatment with deprenyl (0.25 mg/kg s.c. daily for 21 days) caused a significant reduction in tyrosine hydroxylase activity to 60% of control, with no change in the apomorphine-induced reduction of microdialysate DOPA and DOP AC. The reduction in tyrosine hydroxylase activity is compatible with our previous results showing an increase in striatal DA extracellular level following chronic treatment with deprenyl. The increased extracellular striatal DA level could reduce tyrosine hydroxylase activity through activation of a negative feedback loop, by activation of either presynaptic or postsynaptic DA receptors.

Circadian change of dopaminergic neuron activity: effects of constant light and melatonin.

Twenty-four hour profiles of tuberoinfundibular (TI), nigrostriatal and mesolimbic dopaminergic (DA) neuronal activities were assessed in estrogen-primed ovariectomized rats using DOPAC and DOPA levels in terminal regions of DA neurons. Significant decreases in DOPAC and DOPA levels in the median eminence were observed at 17.00 and 21.00 h, which corresponded with higher serum prolactin levels. DOPAC or DOPA levels in the striatum and nucleus accumbens were, however, significantly higher during the dark (21.00-05.00 h) phase. In rats kept under conditions of continuous light, no late afternoon decline in median eminence DOPA was observed; this decline could be reinstated by repeated injections of melatonin between 18.00 and 01.30 h for 3 days. In summary, circadian rhythms of central DA neurons were shown and melatonin may play an entraining role.

Activation of tyrosine hydroxylase in striatum of newborn piglets in response to hypocapnic ischemia and recovery.

The present study describes the effect of hypocapnic ischemia caused by hyperventilation on striatal levels of dopamine, DOPAC, HVA and activity of tyrosine hydroxylase in striatal synaptosomes isolated from the brain of newborn piglets. Hyperventilation did not result in statistically significant changes in the striatal level of dopamine and its major metabolites; however, it was observed that after 20 min of recovery the levels of striatal tissue dopamine, DOPAC and HVA increase by 195%, 110% and 205%, respectively. The level of DOPA (3,4-dihydroxyphenylalanine), which was used as an index of tyrosine hydroxylase activity, also increased after recovery. The rate of dopamine synthesis was 32 pmoles/mg protein/10 min in control piglets and after recovery this increased to 132 pmoles/mg protein/10 min. Measurement of the tyrosine hydroxylase activity in Triton X-100 treated synaptosomes showed that, after 20 min of recovery, there was an increase in Vmax with no change in K(m) for pteridine cofactor, compared to control. This is consistent with the enzyme having been covalently modified (activated) during tissue ischemia caused by hyperventilation and remaining activated well into the recovery period. We postulate that ischemia can induce long lasting alterations in dopamine synthesis, which may play some role in mediation of hypoxic cell injury in immature brain.

Studies on novel, stable and potent competitive antagonists against L-DOPA

DOPA has been proposed to be a neurotransmitter of the primary baroreceptor afferents terminating in the NTS and a neuromodulator in striata of rats. Pre- and post-synaptic recognition sites for DOPA itself may exist. DOPA methyl ester (DOPA ester), a potent competitive antagonist for DOPA in continuously superfused slices or within a several min when microinjected in the NTS has some limitation in in vivo use because of its unstableness as a prodrug for DOPA. We have explored to find stable and potent antagonists for DOPA. At first, we tried to clarify whether or not newly synthesized DOPA esters with bulky structure such as DOPA cyclohexyl ester (CHE), DOPA cyclopentyl ester (CPE) and DOPA cyclopentyldimethyl ester (CPDME) antagonize depressor responses to DOPA microinjected into the NTS, and to what degree these analogues 1 microM perfused via probes are converted to DOPA during striatal microdialysis in urethane-anesthetized rats. Then, we analyzed mode of antagonism of some candidate in the NTS system. During striatal microdialysis, DOPA ester 1 microM increased extracellular levels of DOPA to an 100 fold higher level at a peak of the 1st 20 min sample after the perfusion. Conversion ratio of CHE, CPE and CPDME, compared to DOPA ester, was less than 1/5 at the peak of the 3rd sample, 1/3.3 at the peak of the 2nd, and 1/2.7 at the peak of the 3rd, respectively. In the NTS, all analogues 1 microgram microinjected abolished depressor responses to DOPA 60 ng. Time required to recover a base was 20 min for CHE and 10 min for DOPA ester, CPE and CPDME. At 100 ng, CHE inhibited peak depressor responses to DOPA 60 ng by 53%, CPE by 40%, and CPDME by 24%, compared to DOPA ester by 22%. Then, DOPA 10-300 ng microinjected produced dose-dependent hypotension. DOPA ester 300 ng, microinjected 1 min previously, shifted a dose-response curve for DOPA 30-300 ng to the right without reduction of the maximum response, showing a competitive mode of antagonism. CHE 30 ng competitively antagonized depressor responses to DOPA 18-300 ng without reduction of the maximum response. CHE 100 ng further shifted the dose-response curve for DOPA 18-100 ng to the right with 25% reduction of the maximum response. Antagonistic activity of CHE 100 ng was equipotent with DOPA ester 300 ng. CHE is a competitive antagonist including partially some noncompetitive components. A possible component might be related to NMDA receptors, since high concentrations of CHE displaced selective binding of [3H]-MK-801, an antagonist. In conclusion, CHE is suitable for the purpose.

Plasma catechols and monoamine oxidase metabolites in untreated Parkinson's and Alzheimer's diseases

Prior studies have documented functional and pathological compromise of the peripheral sympathetic nervous system in patients with Parkinson's disease, suggesting the possibility of reduced catecholamine release into the circulation. We measured free plasma catechols in early and untreated patients with Parkinson's disease, but found no evidence of reduced concentrations, compared to control subjects or a group of patients with probable Alzheimer's disease. Rather, there was a significant elevation of plasma norepinephrine within the Parkinson's disease group. Furthermore, 6 of 15 untreated Parkinson's disease patients (40%) displayed markedly elevated plasma concentrations of the catecholamine MAO metabolites, DOPAC or DOPEG. Despite this finding, platelet MAO-B activity measured in these and all other Parkinson's disease patients fell well within the range of the control subjects, and was also statistically similar to the group with Alzheimer's type dementia. Plasma dopa levels were similar in all groups, whereas the majority of patients in the three groups had plasma free dopamine and epinephrine concentrations below the limits of detection. These trends toward increased, rather than decreased, circulating catechol concentrations suggest that peripheral sympathetic nervous system catecholamine production and release is not severely compromised in patients with early Parkinson's disease. In addition, we were unable to confirm certain previous reports of elevated MAO-B activity in patients with Parkinson's or Alzheimer's diseases.

Increased neostriatal tyrosine hydroxylation during stress: role of extracellular dopamine and excitatory amino acids.

We examined the regulation of neostriatal tyrosine hydroxylation during acute stress, testing the hypothesis that excitatory amino acids (EAAs) contribute to the stress-evoked increase in dopamine (DA) synthesis. Dialysis probes implanted into neostriatum permitted delivery of drugs and sampling of extracellular fluid. Rats were exposed to 30 min of intermittent tail shock during infusion of an inhibitor of aromatic amino acid decarboxylase (AAAD), NSD-1015 (100 microM), and DOPA was measured in the dialysate. Tail shock was applied beginning either 15 min after the onset of NSD-1015 treatment (the initial rate of DOPA accumulation) or 75 min after the onset of treatment (when DOPA had approached steady state). Tail shock increased the steady-state levels of extracellular DOPA in neostriatum (+40%). However, there was no change in the initial rate of DOPA accumulation unless animals also received the D2 receptor antagonist eticlopride (50 nM), in which case an increase was observed (+228%). The impact of tail shock on the steady-state level of DOPA was attenuated by the D2 agonist quinpirole (100 microM), or by 2-amino-5-phosphonovalerate (APV) (100 microM) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (100 microM), EAA antagonists acting at NMDA or D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-4-propionate (AMPA) receptors, respectively. These data suggest that acute stress normally has little effect on tyrosine hydroxylation in neostriatum due to the inhibitory influence of DA in the extracellular fluid. However, when that influence is absent (e.g., during extended inhibition of DOPA decarboxylation or blockade of DA receptors), stress increases tyrosine hydroxylation via EAAs acting on NMDA and AMPA receptors. Thus, EAAs released from corticostriatal projections may stimulate DA synthesis and thereby restore dopaminergic activity under conditions in which the availability of DA for release has been compromised.

3,4-dihydroxyphenylalanine (DOPA) metabolism in screening-detected and non-screening-detected neuroblastoma.

To investigate the possible clinical application of the hypothesis that insufficient induction of 3,4-dihydroxyphenylalanine decarboxylase (DDC) causes accumulation and secretion of 3,4-dihydroxyphenylalanine (DOPA) in unfavorable neuroblastomas, we measured plasma DOPA in 28 neuroblastoma patients. Abnormally high levels were demonstrated in patients with neuroblastoma, and the levels in patients with clinical manifestations (median, 44,800 pg/ml; range, 17,700 to 220,000 pg/ml; n = 6) were significantly higher than those in patients detected by screening (median, 5825 pg/ml; range 2890 to 33,300 pg/ml; n = 22) (P = 0.0004). The catecholamine secretion profiles of the two groups were different, and it was suggested that the relative deficiency of DDC caused DOPA secretion in patients in the former group, whose prognosis was unfavorable, except in one case. In both groups, serial determination of plasma DOPA was a good monitor of the disease course. The higher plasma DOPA level (>9400 pg/ml) was significantly correlated with the patients' age (>1 year old) (P = 0.019), tumor stage (III, IV) (P = 0.029), and DNA diploidy (P = 0.018). These results are consistent with previous studies that demonstrated plasma DOPA was a useful marker in the diagnosis and follow-up of neuroblastoma. The results also indicate that higher plasma DOPA levels are associated with the unfavorable characteristics of neuroblastoma, which seem to support the hypothesis on DDC deficiency in unfavorable neuroblastoma.

Sympathoadrenal system in stress. Interaction with the hypothalamic-pituitary-adrenocortical system.

Exposure of an organism to any of a variety of stressors markedly activates the sympathoadrenal and hypothalamic-pituitary-adrenocortical systems. Interactions of these major stress systems occur at several levels in the periphery and the brain. In the present study, we used sham-operated or adrenalectomized cortisol-treated conscious rats to examine glucocorticoid effects on indices of CA release, metabolism, and synthesis, and on CA biosynthetic enzyme activities and gene expression at baseline and during immobilization stress (IMO). Adrenalectomy (ADX) stimulated basal and stress-induced increments in norepinephrine release, reuptake, metabolism, turnover, and biosynthesis. Loss of adrenomedullary hormones after ADX did not appear to contribute to these increments. Cortisol treatment reversed the ADX effects on CA indices and suppressed catecholaminergic responses to IMO in intact rats. These results suggest that endogenous glucocorticoids restrain responses of catecholamine turnover, synthesis, release, reuptake, and metabolism during stress. In contrast, in intact rats, continuous administration of cortisol lasting for 7 days exaggerated the IMO-induced increases in plasma CA levels. Inhibition of DOPA conversion to dopamine elevated plasma DOPA levels in chronically cortisol-treated stressed rats compared to saline-treated ones, suggesting a cortisol-induced increase in tyrosine hydroxylation. Stress increases TH and PNMT activities and mRNA levels in the adrenal medulla. Hypophysectomy reduced adrenal PNMT but not TH mRNA levels in control and IMO rats. Pretreatment of hypophysectomized animals with ACTH fully restored the control and IMO-induced adrenal PNMT mRNA levels and augmented PNMT but not TH mRNA responses in intact rats. Long-term cortisol administration to intact rats also elevated adrenal PNMT but not TH mRNA levels. The results indicate a suppressive effect of endogenous glucocorticoids and a stimulatory effect of chronically elevated glucocorticoid levels on sympathoadrenal activity during stress. The results also suggest that a nonneuronal, nonpituitary factor contributes to TH gene expression during some forms of stress, whereas pituitary-adrenocortical factors play the essential role in the regulation of PNMT gene expression.

Comparison of the effects of 2‐deoxyglucose and immobilization on secretion and synthesis rate of catecholamines in the adrenal gland: a microdialysis study in conscious rats

Using microdialysis, extracellular 3,4-dihydroxyphenylalanine (DOPA), noradrenaline (NA) and adrenaline (AD) concentrations in the adrenal gland were monitored in conscious rats during and after 60 min of immobilization (IMM) as well as after injection of 500 mg kg(-1) 2-deoxyglucose (2-DG). IMM produced a rapid and transient increase in secretion of AD (20-fold), NA (13-fold) and DOPA (3.6-fold). This was accompanied by an increase in blood pressure (+18 mmHG) and heart rate (+146 b.p.m.). Repeated exposure to IMM (daily 60 min, for 5 days) had no influence on either catecholamine secretion of haemodynamic profiles, indicating the lack of habituation to stressful conditions. Unlike IMM, the stress of 2-DG-induced central neuroglucopenia stimulated the release of AD without affecting NA secretion. AD levels peaked (5.1-fold increase) 40-60 min after 2-DG injection and then slowly declined. 2-DG induced no changes in blood pressure but reduced the heart rate (-48 b.p.m.). In separate experiments, steady-state dialysate DOPA levels, reached during continuous infusion of decarboxylase inhibitor NSD 1015 into adrenal gland tissue through the dialysis probe, served as an index of adrenomedullary tyrosine hydroxylase (TH) activity. IMM evoked a marked response in TH activity (DOPA formation increased 2.7-fold), which remained elevated 60 min after the cessation of stress when AD and NA secretion had already fallen to baseline. After 2-DG, despite significant hormonal response, adrenal TH activity was unchanged. These results give clear evidence that IMM and 2-DG-induced neuroglucopenia may be considered as two different types of stressful stimuli.

Dialkyldithiocarbamates inhibit tyrosine hydroxylase activity in PC12 cells and in fibroblasts that express tyrosine hydroxylase

Dithiocarbamates and CS 2 have been associated with neurobehavioural changes suggestive of central dopaminergic dysfunction. Diethyldithiocarbamate (DEDC), dimethyldithiocarbamate (DMDC), and methyldithiocarbamate (MDC) were examined for their ability to inhibit tyrosine hydroxylase (TH) activity in PC12 cells and transfected CHO fibroblasts that expressed TH ( CHO TH ) activity when tetrahydrobiopterin (BH 4) was added to medium. DEDC or DMDC did not significantly alter viability of PC12 cells or CHO TH cells at ≤100 μM for 18 h; the EC50 for each compound was approximately 5 mM in both cell lines. In contrast, the EC50 for MDC was 41 or 74 μM in PC12 or CHO TH cultures, respectively. There was no change in immunodetectable levels of TH in PC12 or CHO TH cells following exposure to subcytotoxic concentrations of dithiocarbamates. DEDC and DMDC (5 to 100 μM) produced concentration-dependent reductions in PC12 cell dopamine and dopac levels as well as in dopa levels in CHO TH cultures. Reduction of PC12 catechols was not due to altered vesicular storage. In vitro PC12 TH activity was 80.2 ± 3.4% or 82.4 ± 2.9% of control following exposure to 100 μM DEDC or DMDC, respectively, and was not fully restored by incubation with Fe 2+. These results show that DEDC and DMDC, but not MDC, are low potency cytotoxins that decrease TH activity in cultured cells through mechanisms other than inhibition of BH 4 biosynthesis or iron chelation.