Growth hormone response to clonidine as a probe of noradrenergic receptor responsiveness in affective disorder patients and controls

The growth hormone (GH) response to the alpha-adrenergic agonist clinidine was blunted in 19 depressed patients compared to 20 controls. The difference remained significant when age- and sex-matches pairs of patients and controls were compared from this sample, either including or excluding subjects with elevated GH baseline levels. Plasma levels of free 3-methoxy-4-hydroxyphenyl-glycol (MHPG) were assayed in blood samples drawn just before the clonidine infusion. A modest negative correlation was found between the plasma MHPG values and the magnitude of the GH responses to clonidine, although baseline plasma MHPG levels were not significantly different between patients and controls. The diminished GH response to clonidine observed suggests that many depressed patients may have decreased alpha-adrenoreceptor responsiveness. Decreased responsiveness may in some cases be associated with relatively increased indices of presynaptic noradrenergic availability. Such a model might have implications for understanding the functional status of the noradrenergic neurotransmitter system in depressed patients and the possible subtyping of affective disorder patients.     

Uncoupling of serotonergic and noradrenergic systems in depression: Preliminary evidence from continuous cerebrospinal fluid sampling

We used the technique of continuous cerebrospinal fluid (CSF) sampling to test the following hypotheses regarding CNS monoaminergic systems in depression:(1) absolute concentrations of the informational substances tryptophan and 5-hydroxyindoleacetic acid (5-HIAA) are altered in the CNS of depressed patients (2) abnormal rhythms of tryptophan and/or 5-HIAA, or defective conversion of tryptophan to serotonin (5HT), exist in the CNS of depressed patients, and (3) the relationship between the CNS 5HT and norepinephrine (NE) systems is disrupted in depressed patients. We obtained 6-h concentration time series of tryptophan, 5-HIAA, NE, and 3-methoxy-4-hydroxyphenylglycol (MHPG) in the CSF of 10 patients with major depression and in 10 normal volunteers. No significant differences in CSF tryptophan, 5-HIAA, NE, or MHPG concentrations or rhythms were observed between normal volunteers and depressed patients. Neither were there differences in the mean tryptophan-to-serotonin ratio. However, a negative linear relationship was observed between mean concentrations of 5-HIAA and NE in the CSF of the normal volunteers (r = 0.916 [r2 = 0.839], df = 9, P < 0.001) while, in contrast, depressed patients showed no such relationship (r = +0.094 [r2 = 0.00877], df = 9, n.s.). Furthermore, the correlation coefficients expressing the relationship between CSF MHPG and CSF 5-HIAA within the normal and depressed groups were significantly different. These data support the hypothesis that a disturbance in the interaction between the serotonergic and noradrenergic systems can exist in depressive illness in the absence of any simple 5HT or NE deficit or surplus. Depression and Anxiety 6:89–94, 1997.© 1997 Wiley-Liss, Inc.     

Studies on the utility of urinary 3,4-dihydroxyphenylethylene-glycol (DHPG) measurement

1. The utility of urinary DHPG measurement as an index of NE function was evaluated in an animal model by determining its excretion following pharmacological manipulations that are known to alter noradrenergic activity.

2. Acute desipramine (DMI) administration (10 mg/kg i.p.b.i.d.) significantly reduced urinary DHPG (−26%) but not MHPG (−18%) excretion.

3. Acute yohimbine administration (5 mg/kg i.p.b.i.d.) significantly increased urinary DHPG and MHPG levels to a similar extent (+46%).

4. These findings suggest that urinary DHPG levels also provide a sensitive indicator reflecting changes in NE neuronal activity. Further, DHPG may be a better measure of NE metabolism than MHPG to assess the efficiency of the NE neuronal uptake system.     

Noradrenergic function and the cortisol response to dexamethasone in depression

Abnormalities of the hypothalamic-pituitary-adrenal (HPA) axis and the noradrenergic system have been reported in depression. To study possible interrelations between these two systems, plasma free 3-methoxy-4-hydroxyphenylglycol (MPHG) was compared with the cortisol response to dexamethasone in 64 depressed patients. Postdexamethasone cortisol nonsuppressors had higher baseline plasma free MHPG values than did cortisol suppressors. Increased severity of some depressive symptoms was associated with increased postdexamethasone cortisol levels. These results indicate that depressed patients with dexamethasone nonsuppression have increased noradrenergic turnover.     

Indices of noradrenergic output in depression

Concentrations of plasma norepinephrine (NE) and plasma-3-methoxy-4-hydroxyphenylglycol (MHPG), blood pressure, and heart rate were measured on 2 days in 25 depressed patients and 25 controls. Comparisons were made between patients and controls, and also between days for both groups, to determine the short-term stability of these measures. The means of the plasma and urinary noradrenergic metabolite measures were not significantly different between groups. The variance of plasma MHPG, plasma NE, and mean blood pressure was greater in the depressed patients than in controls. Blood pressure, plasma MHPG, and plasma NE were relatively stable as suggested by the significant correlations between the 2 days for each of these variables. Plasma NE, plasma MHPG, and the sum of the deaminated urinary metabolites (MHPG and vanillylmandelic acid) were significantly intercorrelated. These results support other data in suggesting that plasma concentrations of NE and MHPG may be useful measures of noradrenergic activity, but may not consistently distinguish depressed patients from controls.     

Treatment with risperidone for 4 weeks increased plasma 3-methoxy-4-hydroxypnenylglycol (MHPG) levels, but did not alter plasma brain-derived neurotrophic factor (BDNF) levels in schizophrenic patients

In the present study, we investigated the effects of risperidone treatment for 4 weeks on plasma levels of 3-methoxy-4-hydroxyphenylglycol (MHPG) and brain-derived neurotrophic factor (BDNF) in 89 schizophrenic patients. We also compared the plasma levels of BDNF and MHPG between the schizophrenic group and 103 sex-and age-matched normal controls. In addition, we investigated the effects of two SNPs of the noradrenaline transporter (NAT) gene on plasma levels of MHPG, BDNF, and clinical improvement. The mean dose of risperidone was 3.8+/-1.4 mg/day. We demonstrated that treatment with risperidone increased plasma MHPG levels, and this increase was associated with an improvement of the negative symptoms of schizophrenia. In contrast, plasma BDNF did not change after 4 weeks of risperidone treatment, and the two SNPs in NAT did not influence the response to risperidone treatment or plasma MHPG and BDNF levels. These results suggest that the enhancement of noradrenergic neurons by risperidone, which occurs independently of the two SNPs of NAT, plays a role in the clinical efficacy of the drug.     

Noradrenergic function in generalized anxiety disorder, major depressive disorder, and healthy subjects

Plasma norepinephrine (NE), free 3-methoxy-4-hydroxyphenethylene glycol (MHPG), and binding of tritiated yohimbine to platelet membranes were measured in 14 patients with generalized anxiety disorder (GAD), who were matched for age and sex with 14 patients with unipolar major depressive disorder (MDD) and 14 normal subjects. Plasma NE and MHPG levels were increased and the number of alpha2-adrenoreceptors (Bmax) was decreased in GAD patients compared with MDD and normal subjects. No differences were found between MDD patients and normal subjects for plasma NE, MHPG, and alpha2-adrenoreceptor binding. Plasma NE and MHPG were significantly correlated in MDD patients and tended toward a significant positive correlation in GAD patients. Plasma MHPG and affinity of binding platelet alpha2-adrenoreceptors (Kd) were significantly correlated in normal subjects. Thus, noradrenergic activity seems to be increased in patients with GAD, but not in patients with MDD. In GAD patients, higher levels of catecholamines may lead to a down-regulation of presynaptic alpha2-adrenoreceptors.     

Plasma and cerebrospinal fluid 3-methoxy-4-hydroxyphenylethylene glycol (MHPG) as indices of brain norepinephrine metabolism in primates

The relationship between MHPG concentration in several brain areas, cisternal CSF and plasma was examined in 26 vervet monkeys. Free MHPG was measured by gas chromatography-mass spectrometry using deuterated MHPG as internal standard. In animals with or without treatment with drugs that alter norepinephrine metabolism, highly significant correlations were found in concentrations of MHPG between the various brain areas, between plasma and CSF, between plasma and brain areas and between CSF and brain areas. The concentration of MHPG in CSF was higher than in plasma and with the exception of occipital cortex, all brain regions contained a higher concentration of MHPG than CSF. This study supports the notion that free MHPG concentrations in plasma and cisternal CSF are useful indices of central noradrenergic activity.     

State dependence of noradrenergic activity in a rapidly cycling bipolar patient

Plasma levels of the major norepinephrine (NE) metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG), were measured in a rapidly cycling bipolar patient and her first-degree relatives. The mood state dependence and the reciprocal relationship between noradrenergic and cholinergic activity were investigated by assessing mood, thought disorder, and plasma MHPG following the infusion of physostigmine. A correlation was found between plasma MHPG and mood states, with exceedingly high levels during mania and hypomania. Levels were significantly decreased by ECT or combined lithium and chlorpromazine administration. A pathologic diurnal MHPG pattern was detected during periods of abnormal mood changes. Infusion of physostigmine led to a prompt reduction in MHPG release and a marked decline in mood-state measurements and the overall level of thought disorder. Muscarinic receptors exerting negative feedback control over the synthesis and/or release of NE may have become supersensitive as a consequence of alpha 2-adrenoceptor densensitization.     

Activation of noradrenergic neurons projecting to the diencephalon following central administration of histamine is mediated by H1 receptors

The effect of histamine on the activity of noradrenergic neurons terminating in discrete regions of the diencephalon was examined in male rats. Noradrenergic neuronal activity was estimated by measuring the concentration of norepinephrine and its metabolite 3-methoxy-4-hydroxyphenylethyleneglycol [MHPG] in the medial zona incerta [MZI] and in the dorsomedial [DMN], periventricular [PeVN] and medial preoptic hypothalamic nuclei [MPN]. The intracerebroventricular administration of histamine effected a time-related increase in MHPG concentrations in the MZI, DMN, PeVN and MPN; these effects were blocked by the H₁ antagonist mepyramine but not the H₂ antagonist zolantidine. Neither mepyramine nor zolantidine affected basal MHPG concentrations in any of the brain regions examined. These results indicate that central administration of histamine increases the activity of noradrenergic neurons projecting to the diencephalon via an action at H₁ but not H₂ receptors.     

Tricyclic-induced mania and MHPG excretion.

In order to evaluate the presumed involvement of altered noradrenergic receptor sensitivity in the switch process from depression into mania, we explored the relationship between pretreatment 3-methoxy-4-hydroxy-phenylglycol (MHPG) and tricyclic-induced mania or hypomania in bipolar depressed patients. Within the group of patients developing mania or hypomania on tricyclics, there was a strong positive correlation between pretreatment 24-hour urinary MHPG and the latency of onset of the episode. This finding is consistent with both the reported differences in MHPG excretion between unipolar and bipolar patients and the postulated noradrenergic involvement in the switch process.     

New studies and perspectives on the noradrenergic receptor system in depression: effects of the alpha 2-adrenergic agonist clonidine

In an attempt to understand the dynamics of noradrenergic function in depression, we evaluated neuroendocrine, biochemical, cardiovascular, and behavioral responses to the acute intravenous administration of the alpha 2-adrenergic agonist, clonidine, in depressed patients and normal controls. Significantly more variance was observed in the depressed patients than the controls for most indices of basal noradrenergic output including plasma norepinephrine (NE) and 3-methoxy-4-hydroxyphenylglycol (MHPG). Growth hormone, plasma MHPG, and heart rate responses to clonidine were reduced in the depressed patients compared to the controls, all suggesting reduced responsiveness of alpha 2-adrenergic receptors in depression. Baseline levels of cortisol were elevated in the depressed patients compared to the controls. Clonidine decreased cortisol to normal levels in the depressed patients but had little effect in the controls. Thus the depressed patients manifested a significantly increased cortisol response to clonidine. These data raise the possibility that the hypercortisolemia of depression may be related to noradrenergic dysfunction. Clonidine also significantly reduced anxiety in the depressed patients, particularly those with elevated basal plasma MHPG, but not in controls. These results suggest that diminished alpha 2-adrenergic responsiveness as documented by decreased endocrine, biochemical, and physiological responses to clonidine may be related to the depressive and anxiety symptoms as well as the neuroendocrine disturbances characteristic of many depressed patients.     

Effect of ventral noradrenergic bundle transection and locus coeruleus lesions on urinary 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) excretion in the rat

Urinary 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) excretion was determined in rats after central noradrenergic pathway interruption by ventral bundle transection or by locus coeruleus (LC) lesions. The transection prevented an increase in urinary MHPG that occurred in sham-operated animals, an effect that was presumed to be due to loss of cerebrospinal fluid (CSF). Electrolytic lesioning of the LC, which was not attended by loss of CSF, had no effect on baseline MHPG excretion but diminished the response to subsequent administration of the alpha-adrenergic blocking agent, phenoxybenzamine (PBZ). Since the contribution of brain MHPG to total urinary MHPG is small, the observed effects of these procedures are most likely due to disrupted central regulation of peripheral sympathetic nerve activity.     

A simplified routine assay for urinary 3-methoxy-4-hydroxyphenylglycol

Summary Urinary 3-methoxy-4-hydroxyphenylglycol (MHPG) level may provide us with a biochemical index for central noradrenergic activity. Previous methods for assaying MHPG in urine often lacked specificity, sensitivity, cost-effectiveness or convenience. We now describe a simplified routine assay for urinary MHPG by high-pressure liquid chromatography using electrochemical detection. For convenience and cost-effectiveness within a typical batch assay of total MHPG, 0.5 mL of urine sample, 50 L of glusulase and 4 g iso-vanillyl alcohol (internal standard) were used to hydrolyze conjugated MHPG at 37 °C overnight. Alternatively, for a same-day operation, it is efficient to hydrolyze the sample at 50 °C for 3 hours. Each sample was separated isocratically on a reversed-phase column (Ultracarb 5 ODS) at 25 °C with the flow rate at 1 mL/min. Intra- and inter-assay coefficients of variation were found to be 4.0% (n=10) and 5.0% (n=27), respectively, for MHPG at a mean concentration of 1.9 mg/L. Sulfatase or glucuronidase can be substituted for glusulase to obtain either sulfate- or glucuronide-conjugated MHPG. This procedure requires smaller sample amounts and less preparation time without compromising sensitivity and reproducibility.     

A pilot study of noradrenergic and HPA axis functioning in PTSD vs. panic disorder

The biological literature in the anxiety disorders has focused on comparisons between patient groups and normal volunteers, with relatively little comparative study of the anxiety disorders. We therefore conducted this pilot study to compare a group of patients with post-traumatic stress disorder (PTSD) (n=7) to a contiguously studied panic disorder group (n=17) and healthy control subjects (n=16) on baseline levels of cortisol and 3-methoxy-4-hydroxyphenylglycol (MHPG), and response to clonidine challenge. Despite the small sample size, highly significant differences were found on the following measures: PTSD patients had lower cortisol, lower MHPG, reduced MHPG volatility to clonidine challenge, and marginally reduced cortisol volatility compared to patients with panic disorder. These biological findings support existing clinical, epidemiologic, family study, and clinical trial findings that distinguish these two disorders as distinct syndromes.     

Disturbances of noradrenergic systems in normal weight bulimia: relationship to diet and menses

Several lines of evidence suggest that noradrenergic (NE) disturbances occur in normal-weight bulimic patients. The purpose of this study was to investigate factors that may be related to noradrenergic disturbances. First, we measured plasma NE during bingeing and vomiting. We found that this behavior activated the sympathetic nervous system. Bingeing produced a significant increase in the duration and the peak increase of plasma NE when compared with normal controls eating a large meal. Second, we assessed basal peripheral and central NE levels near in time (within several days of hospital admission) to chronic bingeing and vomiting. At this time, bulimics had normal basal plasma and CSF NE levels. Finally, we restudied the same patients after 30 days of inpatient hospitalization and observed abstinence from bingeing and vomiting. In this last state, bulimics had a reduction of basal plasma and cerebrospinal fluid (CSF) NE levels compared with themselves on admission and compared with healthy controls. This study confirms that reduced noradrenergic activity occurs in normal-weight bulimic women and suggests that this abnormality may emerge during abstinence from bingeing. We hypothesize that dietary intake is related to noradrenergic activity, but cause and effect remain uncertain. Noradrenergic disturbances did not appear to be related to weight, depression, physical activity, or amino acid precursors. Lower CSF NE levels were found in amenorrheic bulimic women in both states, suggesting that a noradrenergic disturbance may be associated with the frequent incidence of amenorrhea in bulimic women.     

精神分裂症异质性及其中枢去甲肾上腺素功能初步研究

本文采用高压液相色谱（ＨＰＬＣ）对４２例阳性精神分裂症、２５例阴性精神分裂症及１０例健康对照组进行了脑脊液中去甲肾上腺素（ＮＥ）及其代谢产物３－甲基－４－羟基苯乙二醇（ＭＨＰＧ）的测定，同时引入ＮＥ相对代谢率（ＭＨＰＧ／ＮＥ）加以比较，研究结果提示：６７例精神分裂症脑脊液中ＭＨＰＧ明显低于正常对照组，４２例阳性精神分裂症脑脊液中ＮＥ及ＭＨＰＧ亦明显低于正常对照组，同时还发现，阴性精神分裂症相对代谢率ＭＨＰＧ／ＮＥ也明显低于阳性精神分裂症．本文针对以上结果、结合ＮＥ与多巴胺（ＤＡ）的相互关系进行了讨论，同时分析了精神分裂症的异质性问题。     

Noradrenergic function and hypothalamic-pituitary-adrenal axis activity in primary unipolar major depressive disorder

Plasma levels of cortisol, norepinephrine (NE), and 3-methoxy-4-hydroxyphenylglycol (MHPG) were found to be significantly higher in 16 drug-free patients with primary, unipolar major depressive disorder than in 20 controls. Plasma free MHPG and basal cortisol levels showed a significant positive correlation in the controls, but not in the patients. There were, however, significant positive correlations between cortisol and NE, as well as between NE and free MHPG levels in the patients. No correlations were observed between patient plasma NE levels and platelet alpha 2-adrenoceptor or lymphocyte beta-adrenoceptor Kd or Bmax values. These peripheral measures of noradrenergic function are proposed as useful markers for patients with primary, unipolar major depressive disorder with melancholia.     

MHPG excretion in depression

3-Methoxy-4-hydroxyphenylethyleneglycol (MHPG) was measured in 24-hour urine collections obtained from 44 drug-free patients hospitalized for a major depressive disorder. MHPG was significantly lower in a group of three bipolar I patients than in a group of unipolar patients. The excretion of MHPG did not significantly differ among patients classified as psychotic, agitated, or retarded subtypes of depression as compared to patients not assigned to these subtypes.     

Abnormal regulation of noradrenergic function in panic disorders. Effects of clonidine in healthy subjects and patients with agoraphobia and panic disorder

Clonidine hydrochloride, an alpha 2-adrenergic receptor agonist that decreases noradrenergic function, was administered to 21 healthy subjects and 26 drug-free patients with agoraphobia and panic attacks. Clonidine produced significantly greater decreases in plasma MHPG levels and sitting and standing diastolic blood pressure and significantly smaller increases in growth hormone levels and self-rated drowsiness in the patients. These findings indicate that the regulation of noradrenergic activity is aberrant in some patients with panic disorder, since a previous study demonstrated that patients with panic disorder exhibit increased plasma MHPG levels, blood pressure, and behavioral responses to the alpha 2-adrenergic receptor antagonist yohimbine. The increased dynamic range of noradrenergic activity observed as an increased sensitivity to both clonidine and yohimbine may reflect abnormalities in the regulatory inputs to noradrenergic neurons, or dysfunction in the alpha 2-adrenergic receptor effector coupling mechanism or the intracellular effector system.