Plasma dihydroxyphenylalanine (DOPA) is independent of sympathetic activity in humans

Dopamine and renal function and blood pressure regulation

Dopamine is an important regulator of systemic blood pressure via multiple mechanisms. It affects fluid and electrolyte balance by its actions on renal hemodynamics and epithelial ion and water transport and by regulation of hormones and humoral agents. The kidney synthesizes dopamine from circulating or filtered L-DOPA independently from innervation. The major determinants of the renal tubular synthesis/release of dopamine are probably sodium intake and intracellular sodium. Dopamine exerts its actions via two families of cell surface receptors, D1-like receptors comprising D1R and D5R, and D2-like receptors comprising D2R, D3R, and D4R, and by interactions with other G protein-coupled receptors. D1-like receptors are linked to vasodilation, while the effect of D2-like receptors on the vasculature is variable and probably dependent upon the state of nerve activity. Dopamine secreted into the tubular lumen acts mainly via D1-like receptors in an autocrine/paracrine manner to regulate ion transport in the proximal and distal nephron. These effects are mediated mainly by tubular mechanisms and augmented by hemodynamic mechanisms. The natriuretic effect of D1-like receptors is caused by inhibition of ion transport in the apical and basolateral membranes. D2-like receptors participate in the inhibition of ion transport during conditions of euvolemia and moderate volume expansion. Dopamine also controls ion transport and blood pressure by regulating the production of reactive oxygen species and the inflammatory response. Essential hypertension is associated with abnormalities in dopamine production, receptor number, and/or posttranslational modification.

Ingestion of bonito extract ameliorates peripheral blood flow in mice loaded from over crowding stress

Bonito extract (BE) has been shown to improve various fatigue-related symptoms. The possibility that the improvement of blood flow contributes to the improvement of fatigue-related symptoms has been reported. However, even though BE has been found to increase peripheral blood flow in humans, an understanding of its mechanisms has remained elusive. The purpose of the present study is to construct an animal model system with which the blood flow-increasing effects of BE can be examined. Using mice loaded with crowding stress, an attempt was made to reproduce the increases in peripheral blood flow observed in humans after a single administration of BE. In this study, the crowded-condition mice (20 mice/cage) showed significantly increased catecholamine levels (noradrenaline, adrenaline, and dopamine) in their circulating blood and a decreased rate of skin blood perfusion in comparison with the normal-condition mice (6 mice/cage). The rate of skin blood perfusion was significantly increased by BE in the crowded-condition mice in comparison with the controls, but not influenced by BE in the normal-condition mice. This suggests that BE expands the vascular diameter by affecting the constriction of vessels induced by catecholamines.

Clonidine suppresses plasma and cerebrospinal fluid concentrations of TNF-alpha during the perioperative period

The analgesic properties of alpha(2)-agonists are well known. In experimental models, tumor necrosis factor (TNF)-alpha regulates adrenergic responses in the brain. Constitutive TNF-alpha, in brain regions involved in pain perception, is decreased after the administration of clonidine. We investigated patients undergoing lower-extremity revascularization. Seven patients were treated with clonidine 0.2 mg per os (low), and three patients received 0.4 mg per os clonidine (high) before surgery. Eight patients received placebo and served as controls. Continuous spinal anesthesia was provided by insertion of a pliable catheter into the subarachnoid space. Baseline plasma and cerebrospinal fluid (CSF) samples were obtained before injection of local anesthetic. Samples were analyzed for TNF-alpha using a biologic assay. Systemic and central release of catecholamines were assessed by high-pressure liquid chromatography measurement of norepinephrine in plasma and CSF, vanillylmandelic acid and methoxy hydroxyl phenyl glycol in 24-h urinary excretion, respectively. Clonidine 0.2 mg pretreatment decreased TNF-alpha concentrations both in plasma and CSF. Patients receiving clonidine had lower pain visual analog scale scores and required less morphine compared with the Placebo group (P < 0.01). Preoperative administration of clonidine decreased catecholamine release in the periphery, as well as in the central nervous system. A smaller norepinephrine concentration in plasma and CSF, and less secretion of vanillylmandelic acid (P < 0.01) and methoxy hydroxyl phenyl glycol in the urine, were observed. Larger dose clonidine (0.4 mg) resulted in no detectable TNF-alpha in CSF. These results suggest that an interaction between TNF-alpha and the function of adrenergic neurons in the central nervous system may contribute to the sedative and analgesic effects of adrenergic agonists.

IMPLICATIONS

Preoperative administration of clonidine decreases both plasma and cerebrospinal fluid concentrations of inflammatory cytokines, resulting in perioperative analgesia and decreased sympathetic tone.

Clonidine suppresses plasma and cerebrospinal fluid concentrations of TNF-alpha during the perioperative period

The analgesic properties of alpha(2)-agonists are well known. In experimental models, tumor necrosis factor (TNF)-alpha regulates adrenergic responses in the brain. Constitutive TNF-alpha, in brain regions involved in pain perception, is decreased after the administration of clonidine. We investigated patients undergoing lower-extremity revascularization. Seven patients were treated with clonidine 0.2 mg per os (low), and three patients received 0.4 mg per os clonidine (high) before surgery. Eight patients received placebo and served as controls. Continuous spinal anesthesia was provided by insertion of a pliable catheter into the subarachnoid space. Baseline plasma and cerebrospinal fluid (CSF) samples were obtained before injection of local anesthetic. Samples were analyzed for TNF-alpha using a biologic assay. Systemic and central release of catecholamines were assessed by high-pressure liquid chromatography measurement of norepinephrine in plasma and CSF, vanillylmandelic acid and methoxy hydroxyl phenyl glycol in 24-h urinary excretion, respectively. Clonidine 0.2 mg pretreatment decreased TNF-alpha concentrations both in plasma and CSF. Patients receiving clonidine had lower pain visual analog scale scores and required less morphine compared with the Placebo group (P < 0.01). Preoperative administration of clonidine decreased catecholamine release in the periphery, as well as in the central nervous system. A smaller norepinephrine concentration in plasma and CSF, and less secretion of vanillylmandelic acid (P < 0.01) and methoxy hydroxyl phenyl glycol in the urine, were observed. Larger dose clonidine (0.4 mg) resulted in no detectable TNF-alpha in CSF. These results suggest that an interaction between TNF-alpha and the function of adrenergic neurons in the central nervous system may contribute to the sedative and analgesic effects of adrenergic agonists.

IMPLICATIONS

Preoperative administration of clonidine decreases both plasma and cerebrospinal fluid concentrations of inflammatory cytokines, resulting in perioperative analgesia and decreased sympathetic tone.

CSF and plasma concentrations of free norepinephrine, dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), 3,4-dihydroxyphenylalanine (DOPA), and epinephrine in Parkinson's disease

OBJECTIVE

To investigate endogenous cerebrospinal fluid catecholamines in Parkinson's disease.

MATERIAL AND METHODS

Basal concentrations of free norepinephrine (NE), dopamine (DA), epinephrine (E), 3,4-dihydroxyphenylacetic acid (DOPAC) and 3,4-dihydroxyphenylalanine (DOPA) in cerebrospinal fluid (csf) and plasma were measured using reverse-phase HPLC with electrochemical detection in 16 patients with Parkinson's disease and 21 control patients with low back pain.

RESULTS

Parkinsonian patients had significantly decreased values of csf NE and DOPAC, the strong relationship between plasma and csf NE was disrupted and neither was there any age related increase of plasma NE. In l-DOPA treated patients plasma DA and DOPA concentrations were raised and csf DOPAC values were inversely related to severity of disease (Hoehn and Yahr score). Csf E concentrations were also reduced in parkinsonian patients whereas csf DA concentrations were unchanged. Csf DOPA concentrations were insignificantly decreased in parkinsonian patients.

CONCLUSIONS

These results point towards a diffuse neuronal dysfunction in Parkinson's disease and indicate that lumbar csf NE and csf DOPAC are of central nervous origin.

Increase in plasma 3,4-dihydroxyphenylalanine (DOPA) appearance rate after inhibition of DOPA decarboxylase in humans

Concentrations of DOPA in plasma are relatively high as compared to norepinephrine. The significance of plasma DOPA has not been elucidated. One would expect that substantial amounts of DOPA are derived from sympathetic nerves. There appears, however, neither to be a depot of DOPA in nerves nor is there a close correlation between plasma DOPA and sympathetic activity. The aim of the present study was to obtain further information about plasma DOPA by studying DOPA kinetics in healthy humans both with and without inhibition of DOPA decarboxylase by benserazide. Plasma DOPA and other catecholamines were measured by reverse-phase HPLC with electrochemical detection and DOPA clearance and appearance rate were studied using infusion of 3H-DOPA. The plasma clearance of DOPA was 1.02 1 min-1. Approximately 20% of this value could be explained by DOPA being decarboxylated in the kidneys and excreted as dopamine. The DOPA appearance rate was 1.13 micrograms min-1 and the extremities accounted for approximately 1/5 of this value. After inhibition of DOPA decarboxylase by benserazide the DOPA appearance rate increased 7-fold, whereas the DOPA clearance only decreased slightly and insignificantly. These findings are probably explained by two factors: (1) There is normally a large production of DOPA in some tissues from which DOPA spillover into plasma only occurs to a minor extent and tracer DOPA only mixes with this compartments to a small degree; (2) These compartments are permeable to benserazide, which blocks the decarboxylation of DOPA, which then leaves the tissues and spillover to plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of handling or immobilization on plasma levels of 3,4-dihydroxyphenylalanine, catecholamines, and metabolites in rats

In conscious animals, handling and immobilization increase plasma levels of the catecholamines norepinephrine (NE) and epinephrine (EPI). This study examined plasma concentrations of endogenous compounds related to catecholamine synthesis and metabolism during and after exposure to these stressors in conscious rats. Plasma levels of 3,4-dihydroxyphenylalanine (DOPA), NE, EPI, and dopamine (DA), the deaminated catechol metabolites 3,4-dihydroxyphenylglycol (DHPG), and 3,4-dihydroxyphenylacetic acid (DOPAC), and their O-methylated derivatives methoxyhydroxyphenylglycol (MHPG) and homovanillic acid (HVA) were measured using liquid chromatography with electrochemical detection at 1, 3, 5, 20, 60, and 120 min of immobilization. By 1 min of immobilization, plasma NE and EPI levels had already reached peak values, and plasma levels of DOPA, DHPG, DOPAC, and MHPG were increased significantly from baseline, whereas plasma DA and HVA levels were unchanged. During the remainder of the immobilization period, the increased levels of DOPA, NE, and EPI were maintained, whereas levels of the metabolites progressively increased. In animals immobilized briefly (5 min), elevated concentrations of the metabolites persisted after release from the restraint, whereas DOPA and catecholamine levels returned to baseline. Gentle handling for 1 min also significantly increased plasma levels of DOPA, NE, EPI, and the NE metabolites DHPG and MHPG, without increasing levels of DA or HVA. The results show that in conscious rats, immobilization or even gentle handling rapidly increases plasma levels of catecholamines, the catecholamine precursor DOPA, and metabolites of NE and DA, indicating rapid increases in the synthesis, release, reuptake, and metabolism of catecholamines.

Sympathoneural and skeletal muscle contributions to plasma dopa responses in pithed rats

Dihydroxyphenylalanine (DOPA) in plasma has been thought to originate from sympathetic nerve endings and to reflect catecholamine biosynthesis, because changes in DOPA levels follow pharmacologically- or environmentally-induced manipulations that alter turnover of the sympathetic neurotransmitter, norepinephrine (NE). Skeletal muscle may be an additional, non-neural source of circulating DOPA. In the present study we examined sympathoneural and skeletal muscle contributions to DOPA in arterial plasma in pithed rats. Electrical stimulation of the spinal cord causes discharges of sympathetic post-ganglionic neurons, with attendant release of NE into the bloodstream, and discharges of spinal motoneurons, which causes diffuse contraction of skeletal muscle. Stimulation of the spinal cord rapidly elevated arterial plasma concentrations of NE, dihydroxyphenylglycol (DHPG), and DOPA. Pre-treatment with curare, a skeletal muscle relaxant, did not affect the NE and DHPG responses but attenuated the DOPA responses by about 50%. Administration of chlorisondamine, a ganglionic blocker, abolished NE and DHPG responses to cord stimulation, and DOPA responses were decreased by about 90%. Adrenal-demedullation did not affect the stimulation-induced DOPA responses. The results demonstrate that in pithed rats undergoing spinal cord stimulation, DOPA is released into the bloodstream. Since this response is markedly inhibited after ganglionic blockade and also attenuated after skeletal muscle paralysis, the results provide indirect evidence that DOPA formed in sympathetic neurons can be stored in a non-neuronal pool and released during skeletal muscle contraction.

Monocyte chemotactic activity in sera after hypnotically induced emotional states

In a number of studies it has been shown that psychological factors in general and specifically emotional factors can be correlated to changes in immunological function and defence mechanisms. Although the mediating pathways between the central nervous system and the immune system still remain unclear, it is known that some of the 'classical stress hormones' such as cortisol and catecholamines have modulatory effects on different immunological parameters. In this investigation we wished to study the effect of brief hypnotically induced emotional states on monocyte chemotaxis and endocrinological parameters. Eleven highly hypnotically susceptible volunteers were, while in a deep trance, given suggestions to re-experience earlier life experiences involving intense anger and depression in random order. Before concluding hypnosis subjects were given suggestions to re-experience a feeling of happiness and well-being. Monocyte chemotactic activity in sera and serum levels of cortisol, as well as venous plasma levels of the catecholamines epinephrine, norepinephrine, DOPA and DOPAC, were measured before hypnosis, after each emotional state and immediately after hypnosis. The results showed a significant differences (P less than 0.02) in chemotactic activity between the angry and the depressed emotional states, the depressed state exhibiting a decreased chemotactic index compared with the angry state. Chemotactic index after the happy relaxed emotional state also showed a significant (P less than 0.01) increase compared with both chemotactic index before hypnosis and chemotactic activity after the angry and depressed state. Though there were significant differences between emotions and between emotions and the before-hypnosis-condition, no clear-cut significant differences between the emotional states of anger and depression could be detected for serum cortisol levels and catecholamine plasma levels. Significant positive correlations (P less than 0.01) for differences in chemotactic activity and differences in plasma DOPA levels between emotional states was found. When investigated in vitro, DOPA did not in itself exhibit monocyte chemotactic properties. No other significant correlations between differences in chemotactic activity and other endocrinological parameters could be detected. Soluble interleukin-2 receptors in serum were also measured. No significant differences were found.

The biochemical assessment of sympathoadrenal activity in man

Sympathoadrenal activity in man can be assessed by measuring catecholamines in plasma or by recording impulses in sympathetic nerves to skin and muscles by microneurography. Several studies have indicated that forearm venous plasma noradrenaline concentration and muscle sympathetic nerve activity are closely correlated in normal subjects at rest as well as during various conditions with increased or decreased sympathetic activity. Both parameters are influenced by baroreceptors and increase with age. Plasma adrenaline should preferably be measured in arterial blood because the extraction of adrenaline in organs and tissues may increase considerably when plasma adrenaline increases. The problem of studying the metabolic clearance rate of noradrenaline but not of adrenaline is discussed. It is emphasized that sympathetic activity is highly differentiated and it should therefore be measured in specific organs and tissues. Sympathetic activity in internal organs can be studied by measuring the release of noradrenaline from these organs. Imaging technique may, however, prove useful in future studies. The significance of microdialysis, measurements of plasma catecholamine metabolites, dopa and dopamine, plasma neuropeptide Y, catecholamines in urine and in the cerebrospinal fluid is discussed. Furthermore, it is emphasized that adrenergic agonist and antagonist drugs are important tools to study sensitivity and responsiveness to catecholamines preferably in specific organs and tissues. Finally, a few examples are given of the values in human research of the techniques described.

The relationship between age and venous plasma concentrations of noradrenaline, catecholamine metabolites, DOPA and neuropeptide Y-like immunoreactivity in normal human subjects

Forearm venous plasma concentrations of noradrenaline (NA), catecholamine metabolites (dihydroxyphenylglycol (DHPG), dihydroxyphenylacetic acid (DOPAC], dihydroxyphenylalanine (DOPA) and neuropeptide Y-like immunoreactivity (NPY-LI) were studied in 22 men aged 20 to 81 years in the supine position and after 30 min of standing posture. Venous plasma NA, DHPG and NPY-LI increased significantly in the standing position, whereas venous plasma DOPAC and venous plasma DOPA remained unchanged. Increments in venous plasma NA and DHPG upon standing up, as well as venous plasma NA in the standing-up position, increased significantly with age. The ratio between increments in venous plasma DHPG and venous plasma NA did not change with age. Venous plasma NPY-LI and venous plasma DOPA did not change with age, whereas venous plasma DOPAC decreased significantly. Changes in venous plasma NPY-LI were negatively correlated with changes in pulse pressure. These results confirm previous studies that sympathetic activity increases with age. The unchanged ratio between increments in venous plasma DHPG and venous plasma NA suggests that intra-neuronal deamination of recaptured NA is unchanged in the elderly. The lower basal venous plasma DOPAC concentration may suggest a reduced basal intraneuronal synthesis of NA in old age.

Assessment of sympathoneural activity in clinical research

The assessment of autonomic nervous activity is a frequent and challenging goal of clinical research. The diverse current approaches are reviewed. Direct recording from the sympathetic input to muscle has the advantage of excellent time resolution and directness, but gives no information on the sympathetic input to the internal organs. Plasma noradrenaline concentration has limitations of specificity, some of which are overcome by single isotope radiotracer kinetic techniques. Other chemical markers are less satisfactory. End organ responses are generally limited to cardiovascular and cutaneous autonomic assessment, but sophisticated information is obtainable using power spectral analysis of heart rate variability. Assessment of receptor systems, of first and second messengers and radionuclide imaging of adrenergic nerves all give complimentary information. It is likely that a combination of these diverse techniques will advance understanding of the role of the autonomic nervous system in many disease states.