Catecholamines are biogenic amines and perform important functions as neurotransmitters and hormones. The best-known substances from this group are the stress hormones epinephrine and norepinephrine. When the adrenal medulla is underfunctioning, an undersupply of catecholamines sets in, accompanied by fainting spells.
What are catecholamines?
Catecholamines are biogenic amines that appear particularly as neurotransmitters. They originate from the endocrine glands of the adrenal medulla and are produced with the involvement of the sympathetic nervous system. They bind to the so-called alpha and beta receptors and show a stimulating effect on the circulation. The best known representatives of this group are the stress hormones adrenaline, noradrenaline and dopamine. As stress hormones, catecholamines have a prompt effect because of their binding to the alpha and beta receptors. This distinguishes them from glucocorticoids such as cortisol, which do not come into action quickly enough during sudden short-term stress. Epinephrine was the first hormone to be extracted, researched, and artificially produced. Catecholamines are mimicked by many drugs and are used in critical care medicine to treat shock and allergic reactions.
Anatomy and structure
The catecholamines are involved in biosyntheses. Biosynthesis of these substances occurs in the adrenal medulla and catecholaminergic neurons. Here, the amino acid tyrosine is first converted to levodopa by the enzyme tyrosine hydroxylase. From this levodopa, the aromatic L-amino acid decarboxylase makes dopamine. In dopamine beta-hydroxylase, dopamine is converted to norepinephrine as needed. Norepinephrine can become epinephrine by methylation. This last conversion is catalyzed by phenylethanolamine N-methyltransferase. Catecholamines can also be inactivated. This inactivation corresponds to their uptake into cells and their degradation by catechol-O-methyltransferase or monoamine oxidase. By their structure, catecholamines stimulate alpha-1 and beta receptors in the heart, bronchi, gastrointestinal tract, and blood vessels.
Function and roles
Catecholamines are secreted in the adrenal medulla by action of the sympathetic nervous system. Their purpose is to ensure survival during sudden stress. Evolutionarily, flight and fight are among the most important survival strategies. For both strategies, the body requires an excess of energy. This energy is provided by catecholamines. They have an effect on the circulatory system, have a stabilizing effect and enable people to go beyond their limits. Catecholamines decentralize and thus ensure that the heart and internal organs are still supplied with blood even in the event of blood loss. All catecholamines act on G-protein-coupled receptors. These receptors are either adrenergic or dopamine receptors and are located in both the vascular system and internal organs. There are significant differences between the effects of individual catecholamines. While some of them stimulate the receptors, others block certain receptors. Norepinephrine, for example, blocks the repeated release of catecholamines. Adrenaline, on the other hand, increases blood pressure and heart rate. Norepinephrine increases blood pressure only and shows little effect on rate. Dopamine, in turn, positively affects the contractility of the heart. Thus, stimulation of dopaminergic receptors raises renal, cerebral, and mesenteric blood flow. In contrast, when beta-2 receptors are stimulated, metabolism increases, vascular resistance decreases, and bronchi and vessels dilate. Stimulation of beta-1 receptors on the heart, in turn, causes cardiac strength, heart rate, and excitability of the heart to increase. Gastrointestinal movements are usually throttled by catecholamines. Thus, the effects of catecholamines are numerous and affect the nervous system to the same degree as the metabolic system, the blood system, and the cardiovascular system.
Diseases
A rare disease associated with catecholamines is pheochromocytoma. This involves the formation of a hormone-producing tumor of the adrenal medulla. To be distinguished from this is the paraganglioma. This is a hormone-producing tumor of the sympathetic border cord in the spinal column.Both tumor diseases can cause similar symptoms, because in both the adrenal medulla produces increased adrenaline and noradrenaline. More rarely, there is also an overproduction of dopamine. Due to the circulatory stimulating effect of the stress hormones, high blood pressure sets in. Heart palpitations and sweating are among the most common symptoms. Headaches, tremors and weight loss also occur with this condition. Inner restlessness and panic set in. Due to the increased adrenaline level, blood sugar also rises and after a certain time can promote diabetes as a secondary disease. In most cases, hormone-producing tumors are benign. The tumors occur mainly in the context of various hereditary diseases, such as Hippel-Lindau syndrome. Somewhat more frequently than hormone-producing tumors of the adrenal medulla, underfunctions of the adrenal glands occur. Such underfunctions can occur, for example, after surgery in the area of the kidneys. As soon as the body produces too few catecholamines, blood pressure can only be maintained with difficulty. Dizzy spells with fainting attacks set in. Something similar happens in Waterhouse-Friedrichsen syndrome. This is a complete failure of the adrenal glands preceded by pneumococcal or meningococcal infection. While hormone-producing tumors are usually removed surgically, physicians treat hypofunction of the adrenal medulla by administering catecholamines. The administration of catecholamines also plays a role in emergency medicine and may be necessary here, for example, after resuscitation.
