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Determination of catecholamines, serotonin and their metabolites

Catecholamines are physiologically active substances belonging to biogenic monoamines; they are mediators (noradrenaline, dopamine) and hormones (adrenaline, noradrenaline) of sympathoadrenal system. The main regulatory influence of sympathoadrenal system is carried out through adrenal medulla and adrenergic neurons.

Adrenaline:
Hormone synthesized by chromaffin cells of adrenal medulla. The action of adrenaline is connected with influence on α-and β-adrenergic receptors and coincides to a large extent with the effects of excitation of sympathetic nerve fibers.
The action of adrenaline increases heart rate, increases blood pressure, reduces blood flow to internal organs, increases blood flow to skeletal muscles, increases glucose level in blood, causes the liver and muscle cells to split glycogen and produce glucose, and etc.
Adrenaline stimulates the central nervous system, although it slightly crosses the blood-brain barrier. It increases wakefulness level, mental energy and activity, causes psychological mobilization, response of orientation and feeling of anxiety, jittery or stress, it is generated in borderline situations.
Also adrenaline has a marked anti-allergic and anti-inflammatory effect, inhibits the release of histamine, serotonin, kinins and other mediators of allergy and inflammation from mast cells; reduces tissue sensitivity to these substances.
Adrenaline causes an increase in the number of leukocytes in blood, causes an increase in the number and functional activity of platelets, which, along with spasm of small capillaries, causes haemostatic (styptic), action of adrenaline.

Noradrenaline:
It is a catecholamine, which is produced mainly by postganglionic sympathetic nervous system cells, and to a lesser extent – by the cells of adrenal medulla; it is a mediator of autonomic nervous system, acting directly in area of presynaptic terminals. It belongs to the most important neurotransmitters of brain. It is a precursor of adrenaline.
Noradrenaline is a transmitter of a brain axis locus coeruleus, as well as of terminals of the sympathetic nervous system. The number of noradrenergic neurons in the CNS is small (several thousand), but they have a very wide field of innervation in the brain.
The action of noradrenaline is connected with a predominant effect on the α-adrenergic receptors. Noradrenaline differs from adrenaline with its much more powerful vasoconstrictor and pressor effects, much less stimulating effect on heart contraction, weak effect on the smooth muscles of bronchi and intestine, weak effect on metabolism (the absence of pronounced hyperglycemic, lipolytic and general catabolic effect). Noradrenaline increases the need of the myocardium and other tissues for oxygen to a lesser extent than adrenaline.
Noradrenaline is involved in regulation of arterial blood pressure and peripheral vascular resistance. Cardiotropic action of noradrenaline is associated with its stimulating effect on β-adrenergic receptors of heart.

Dopamine:
Neurotransmitter synthesized in chromaffin cells of specific brain structures, as well as a hormone produced by adrenal medulla and other tissues (e.g. kidneys). Dopamine is a precursor of noradrenaline and adrenaline in their biosynthesis.
Dopamine is one of the chemical factors of internal reinforcement (FIR). It is produced while having pleasure. Like most of these factors, dopamine has narcotic analogs such as amphetamines, ecstasy, ephedrine.
In the extrapyramidal system, dopamine plays a role of stimulating neurotransmitter that promotes physical activity, reduction of motor inhibition and stiffness, reduction of muscle hypertonia. Physiological antagonists of dopamine in the extrapyramidal system are acetylcholine and GABA. In hypothalamus and pituitary, dopamine plays a role of natural inhibitory neurotransmitter inhibiting secretion of several hormones.
Dopamine causes an increase in peripheral vascular resistance. It increases systolic blood pressure. Dopamine also increases heart contractions force. Cardiac output is increased. The heart rate increases, but not as much as under the influence of adrenaline. Myocardial oxygen demand under the influence of dopamine increases.
Dopamine reduces renal vascular resistance, increases blood flow in them, and renal filtration. However, in high concentrations it can cause narrowing of renal vessels. It also inhibits synthesis of aldosterone in the adrenal cortex, reduces renin secretion by the kidneys, and increases secretion of prostaglandins by kidneys tissue.
Dopamine inhibits motility of stomach and intestines. In the CNS, dopamine stimulates chemoreceptors of trigger zone and vomiting center, and thus participates in the act of vomiting.

Serotonin:
5-hydroxytryptamine, 5-HT, is an important neurotransmitter and hormone. By its chemical structure, serotonin relates to biogenic amines, tryptamine class. Serotonin plays a role of neurotransmitter in the CNS. Serotonergic neurons are grouped in the brain stem: in pons varolii and raphes nuclei. From pons varolii descending projection come to the spinal cord, neurons of raphes nuclei give ascending projections to the cerebellum, limbic system, basal ganglia, and cortex. Serotonin along with dopamine plays an important role in the mechanisms of hypothalamic regulation of hormonal pituitary function. Stimulation of serotonergic paths that connect the hypothalamus to the pituitary gland, increases secretion of prolactin and some other hormones of the anterior pituitary gland. Serotonin is involved in regulation of vascular tone.
Serotonin plays an important role in blood clotting. Serotonin increases the functional activity of platelets and their tendency to aggregation and thrombus formation.
Serotonin is involved in the processes of allergy and inflammation. It increases vascular permeability, enhances chemotaxis and migration of leukocytes to focus of inflammation, increases eosinophils count in blood, enhances mast cell degranulation and release of other mediators of allergy and inflammation. Serotonin along with histamine and prostaglandins, stimulating receptors in tissues, plays a role in occurrence of algetic impulsation in injury area or inflammation
Also, a large amount of serotonin is produced in bowels. Serotonin plays an important role in regulation of motility and secretion in gastrointestinal tract, increasing its peristalsis and secretory activity, and many other things.
Their metabolic products are of great importance in the diagnostics of excretion levels of catecholamine and serotonin.
Products of metabolism of catecholamines and serotonin are following:
  • Metanephrine, normetanephrine: intermediate metabolites of adrenaline and noradrenaline.
  • Vanillylmandelic acid (VMA) - the main metabolite of adrenaline and noradrenaline
  • Homovanillic acid (НVА) - the main metabolite of dopamine.
  • 5-hydroxyindoleacetic acid (5-НIAA) - the main metabolite of serotonin

Metabolites in delayed way reflect the fact of raise of production of catecholamines, their increased metabolism. It is detected in daily urine.

Diagnostic value of determining the level of endogenous catecholamines, serotonin and their metabolites.

Oncology

Pheochromocytoma
Pheochromocytoma: functioning tumor (usually benign, rarely malignant) of adrenal medulla or chromaffin tissue outside adrenal gland (paraganglioma, ganglioneuroma, neuroblastoma). In 75% of cases, pheochromocytoma is located in one of the adrenal glands, often in the right. In 10% of all cases the tumor can be detected in both adrenal glands. The remaining 15% of tumors are located outside the adrenal gland. In 10-20% of cases during the study of tumors, histological signs of malignant growth can be identified.
As a rule, pheochromocytoma secretes adrenaline as well as noradrenaline, but predominantly noradrenaline. Some tumors secrete only noradrenaline or (rarely) only adrenaline. Very rarely predominant catecholamine is dopamine. In addition to catecholamines, pheochromocytoma can produce serotonin, ACTH, somatostatin, opioid peptides, calcitonin, neuropeptide Y (strong vasoconstrictor), etc.
Clinical presentations. Complaints: headaches, palpitations, irritability, weight loss, chest pain or abdominal pain, nausea, vomiting, weakness and fatigue. Objective signs: changes in blood pressure (in 98% of patients), persistent hypertension, hypertensive crises (may be replaced by hypotension), orthostatic hypotension, increased blood pressure after minor physical activity (e.g., after meals or defecation) or physical examination (e.g., after palpation of abdomen), paradoxical increase in blood pressure in response to some antihypertensive drugs, sharp increase in blood pressure during general anesthesia.
Other signs of excess of catecholamines: sweating, tachycardia, arrhythmia, reflectory bradycardia, increased apical impulse, pale skin of face and body, agitation, anxiety, fear, hypertensive retinopathy, dilated pupils; very rarely - exophthalmos, tearing, paleness or hyperaemia of sclerae, lack of response the pupil to light, tremor, Raynaud syndrome, or marbling of skin; in children sometimes edema and cyanosis of hands is detected; wet, cold, clammy and pale skin of hands and feet, “goose bumps”, cyanosis of nail beds.
Complications of pheochromocytoma:
  • a myocardial infarction
  • heart failure, arrhythmia, tachycardia, increase in blood pressure or stagnation of circulation during administration of general anesthesia, shock, cerebrovascular disease
  • renal failure
  • hypertensive encephalopathy
  • ischemic colitis, dissecting aortic aneurysm
  • fever in pregnant women, eclampsia, shock, death of the mother or fetus
  • etc.
In patients with pheochromocytoma catecholamine concentration in blood is increased by 10-100 times. In this case:
pheochromocytomas of adrenal origin: growth of level both adrenaline and noradrenaline, as well as their intermediate and final metabolites.
extraadrenal tumors (paraganglioma, ganglionevroma, neuroblastoma, etc.): usually increases only the content of noradrenaline, normetanephrine.
Study of catecholamines level in the dynamics enables not only to diagnose pheochromocytoma, but also to monitor the effectiveness of the therapy held:
Eradication of tumor: always accompanied by a rapid normalization of indicators
Recurrence of the process: leads to re-raising the concentration of catecholamines in blood.

During the study of catecholamines, not only determination of their levels in plasma is informative, but also urinary excretion and determination in urine of metabolites of catecholamines. However, it should be noted that each method has its disadvantages:
For example, sufficiently rapid elimination of catecholamines in blood is detected and, ideally, blood samples for this study should be done at the time of striking clinical manifestations (hypertensive crisis, etc.), which is not always feasible in practice.
Detection of catecholamines and their metabolites in urine may not be sufficiently informative, if the patient has impaired renal function.
Therefore, the best option is to study adrenaline, noradrenaline, and their intermediate metabolites (metanephrine, normetanephrine) in blood with simultaneous detection of excretion of catecholamines and their terminal metabolites (VMA) in urine.

Diagnostic significance of the level of serotonin in oncology

About 90% of serotonin is synthesized and stored in enterochromaffin cells of gastrointestinal tract, it comes from it to blood and is absorbed by platelets, causing their aggregation. Serotonin has a significant effect on endocrine system, affecting both synthesis of hypothalamic factors and functioning of peripheral endocrine glands.

In clinical practice:
Detection of serotonin level in blood is the most informative in malignant tumors of stomach, intestines and lungs, when this indicator exceeds the norm by 5-10 times. At that increased content of metabolic products of serotonin in urine is revealed. After radical tumor surgery there is a complete normalization of these parameters, and therefore the study of serotonin levels in blood and daily urine in the dynamics enables to evaluate the effectiveness of the therapy carried out.
Recurrence of the process or metastasis: re-raise of serotonin levels in blood and of excretion of metabolites in urine. Serotonin and 5-HIAA are markers of malignancy.
Other possible reasons of increase of serotonin levels in blood and urine are medullary thyroid cancer, acute intestinal obstruction, dumping syndrome, cystic fibrosis, acute myocardial infarction

Cardiology.

Arterial hypertension. The sympathetic part of the autonomic nervous system is a major system of systemic blood pressure regulation. It refers to short-term mechanisms of regulation of blood pressure. Importance of autonomic nervous system is also determined by the fact that it affects directly on two parameters which determine the magnitude of blood pressure - the force of heart contractions, i.e., the pumping function of the heart, and tone of resistive peripheral vessels.
Diagnostic value of level of catecholamines and their metabolites. Inadequate prolonged hypercatecholaminemia or hypocatecholaminemia caused by disturbance of synthesis, secretion, inactivation or excretion of catecholamines, as well as change in sensitivity of tissues adrenergic receptors to certain catecholamines lead to a breach of physiological balance of blood pressure-forming factors, development of persistent abnormal hyper-or hypotensive states.
Long hypercatecholaminemias are especially dangerous, as a result of increased production or activity (e.g., due to a genetic defect of receptor system) of catecholamines resistant arterial hypertension is developed, characterized by crisis course, myocardial hypertrophy with subsequent myogenic dilation. The causes of these pathological conditions are the following:
Catecholamines stimulate spasm of subcutaneous and visceral vessels, mucous membranes and kidneys through interaction with a-adrenergic receptors, thereby increasing the total peripheral resistance (TPR).
Influence of catecholamines on heart muscle (mediated via b1-adrenergic receptors) leads to an increase in heart rate, increased myocardial contractility and increase the rate of conductivity.
Catecholamines also increase cardiac output by stimulating constrictions of veins, increasing of venous return and atrial force of contraction, thereby causing an increase in diastolic volume, and hence the length of the fibers.
With an increase in blood pressure in the system of afferent arteries of the kidneys glomerular filtration capacity changes, mechanism of renin-angiotensin-aldosterone system (RAAS) is started, resulting in increases of BCC, as well as one of the products (angiotensin II) has a direct vasoconstricting effect.

Neuropsychiatry.

Monoamines and indolealkylamines are very important class of neuromodulators.
Dopamine is an inhibitory modulator, which reduces the effects of the excitatory neurotransmitter acetylcholine. It contribute to euphrasia and emotional satisfaction, as well as non-standard brain activity (including, probably, creative activity).
Noradrenaline causes an accumulation in the cell of Ca 2 + ions (through α1-adrenergic receptors) and cAMP (through β-adrenergic receptors). Reticular formation of the stem is activated, which tones the brain, including the cerebral cortex. It stimulates memory, purposive behavior, emotions and thinking. Administration of substances that reduce the accumulation of CA in the nerve cells (reserpine) sharply reduces brain activity. Noradrenaline is released from sympathetic nerve endings into the synapse and then into blood in anger, rage, psychological mobilization.
Serotonin reduces aggression, fear, depression, stimulates feeding behavior, sleep, and fall into winter hibernation, increases food reflexes and decreases pain reflexes, promotes learning capacity and leadership.

Parkinsonism, extrapyramidal hyperkinesia
Parkinson disease is a chronic progressive neurodegenerative syndrome characterized by motor disorders such as hypokinesia, tremor and muscle rigidity; impaired autonomic regulation and mental activity due to injuries of extrapyramidal system. The disease incidence of Parkinson disease increases with age.
In the current understanding of pathophysiology of Parkinson disease, main role is given to degeneration of dopaminergic neurons in the substantia nigra compact zone, to a lesser extent to noradrenergic locus coeruleus neurons.
The compact zone of the substantia nigra sends their projections to the striatum, which is an integral center of stereotypical motor reflex of muscles and regulates motion, muscle tone and walking. Dopamine is the primary inhibitory neurotransmitter in the striatum. Changing in concentration of dopamine has functional effects on other mediators.
Diagnosis of Parkinson disease:
· Determination of content of the main metabolite of dopamine – homovanillic acid (NVA). When Parkinson disease it is significantly reduced.
· When extrapyramidal hyperkinesias, identification of main metabolites of dopamine and noradrenaline of homovanillic acid (NVA) and vanillilmandelic acid (VMA), an intermediate metabolite of noradrenaline-normetanephrine

Depressions.
Depression, according to WHO, at the moment is one of the most common psychopathological disorders. The clinical pattern of depressive syndrome is characterized by a primary triad of symptoms, known for years: low, depressed mood, and ideational and motor inhibition.
Genesis of affective disorders is caused by abnormal functioning of brain structures, in particular the limbic-thalamic and pituitary-hypothalamic. In this case the limbic system is the main coordinator forming an integrative circuit through which the cortical centers of the regulation of emotions send impulses to the hypothalamus, and hypothalamic impulses are transmitted to hippocampus.
One of the main neurochemical mechanisms of depressions formation is a depletion of catecholamine neurotransmitter system. In addition, formation of affective disorders is caused by an imbalance (hypo-, hyper-or dysfunction) of interactions between the noradrenergic, serotonergic, and peptidergic systems.
Metabolites of catecholamines and serotonin have the diagnostic significance for identifying the causes of depressive states, as well as evaluation of the held therapy:
  • VMA (vanillylmandelic acid), the main metabolite of adrenaline and noradrenaline
  • 5-HIAA (5-hydroxyindoleacetic acid) - the main metabolite of serotonin
  • The level of serotonin in blood plasma can provide an accurate information regarding the level of active transmitter at central synapses synoptic gap.

It is important to note that treatment with antidepressants and antipsychotic drugs should be conducted under medical supervision and in accordance with the peculiarities of each individual organism. It is therefore necessary to identify qualitatively pathogenic variant and conduct therapeutic drug monitoring.

Epilepsy, epileptic syndrome.
Repeated convulsive (more common) or non-convulsive attacks arising when extensively proceeding cerebral pathological processes (tumor, brain injury, neuroinfection, vascular pathology, metabolism disorders, etc.) or when their expressed after-effects. Seizures usually disappear after removal of neurological pathology.
In the process of central nervous regulation of the autonomic functions, involvement of catecholamines and serotonin has great importance. As both hormones and neurotransmitters of sympathetic-adrenal system, catecholamines are involved in development of adaptive reactions of the organism.
There is a certain relationship between the nature of convulsive seizure and the level of catecholamine excretion in urine. Usually a large convulsive seizure follows (prior one day) an increased excretion of noradrenaline, its metabolite. In case of frequent large seizures a declined catecholamine excretion is marked, that indicates a certain functional depletion of sympathetic-adrenal system.
Determination of level of catecholamines, serotonin and their metabolites in urine has diagnostic significance.

Schizophrenia.
Schizophrenia is a disease of brain, which violates a person's ability to think correctly, to control his emotions, make decisions and communicate with other people.
Among the biological theories of schizophrenia the neurotransmitter one, dopamine in particular, is currently the most widespread.
Dopamine theory: in case of this disease there is an increase in activity of the brain dopamine system with increase in dopamine release, increase in dopamine neurotransmission and dopamine receptors hypersensitivity, i.e., it is assumed that dopamine neurons are in hyperactive state.
Serotonin theory: the development of schizophrenia is caused by deficiency of serotonergic neurotransmission. This hypothesis was created on the basis of observations of psychotomimetic action of lysergic acid diethylamide (LSD), which is a blocker of serotonin receptors.
Noradrenergic hypothesis: schizophrenia is based on degeneration of noradrenergic neurons. The appearance of this hypothesis to some extent was influenced by observing the effects of 6-oxidophamine, which as a neurotoxin affects selectively noradrenergic neurons. Noradrenergic neurotransmission deficit may explain not only the occurrence of symptoms of acute schizophrenia, but also the development of defect states and negative presentations of the disease (loss of energy potential, anhedonia, etc.).

Drug and alcohol addiction.
When the primary samples of narcotic drugs, the activation of positive reinforcement system occurs, which primarily becomes evident in rapid receptor and metabolic changes, mainly in the monoamines and opioid systems. Apparently, these changes lead to formation of morbid attraction.

With long-term narcotic drug use deficiency of neurotransmitters may develop, in itself threatening life of the organism. As a mechanism of compensation of this phenomenon there is the intensive synthesis of catecholamines and inhibition of enzymes activity of their metabolism, especially monoamine oxidase and dopamine-b-hydroxylase, which control the conversion of dopamine to noradrenaline. Thus, release of catecholamines stimulated by another narcotic drug administration, and their rapid excessive destruction are combined with compensatory increased synthesis of these neurotransmitters. Accelerated circulation of catecholamines is formed. Now, when administration of narcotic drug is terminated, i.e. in case of abstinency, there is no enhanced release of catecholamines from the depot occurs, but their accelerated synthesis is maintained. Due to changes in enzymes activity in biological fluids and tissues (mainly in brain) dopamine accumulates. This process leads to development of basic clinical signs of abstinence symptoms - high anxiety, tension, excitement, increased blood pressure, increased heart rate, occurrence of other autonomic disorders, sleep disorders, etc. In other words, the above changes of neurochemical brain functions form a physical dependence on narcotic drugs.
Dopamine levels in blood correlates clearly with clinical severity of abstinence symptom: in the beginning of its period it is somewhat elevated, then usually falls below the norm. Obviously, the deficit of dopamine in the brain structures associated with reinforcement, is the basis of the remaining morbid attraction to narcotic drugs and a high probability of the disease recurrence.
The action of dopamine and serotonin is associated with mood, emotions, motivations, goal-oriented behavior, attention, thinking process before doing something ... If serotonin metabolism is impaired, the balance of serotonin and dopamine is changed, all of these important mental functions will be affected, and the organism will start to look for a way to eliminate the discomfort: morbid attraction to alcohol, narcotic drugs, candies, cigarettes will occur... By different biochemical pathways nicotine, narcotic drugs, alcohol, glucose may temporarily reduce or even completely compensate the emotional stress, bad mood, distract from the feeling of failure to reach a goal, and healthy people knew it to own cost.
In patients with drug and alcohol addiction:
  • elevated value of catecholamine metabolites HVA and VMA is revealed
  • decreased concentration of 5-HIAA is revealed.