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The catecholamine group, which includes dopamine, noradrenaline (norepinephrine), and adrenaline (epinephrine), is responsible for the neurotransmitter and hormone roles that these chemicals play in the human body. The body produces these three substances, which are found in nature. Unlike the other catecholamines, isoprenaline is synthesized and not found in the body naturally. It is important to discuss because it has pharmacological significance. As the name implies, it is an amine group (a group that contains nitrogen) that is joined to a catechol group (a benzene ring with two hydroxyl groups), as shown in figure 1.
At rest, thermogenesis—the production of body heat—and nutrient metabolism are the two main functions of catecholamines. During a stressful event, specific catecholamines will encourage the body to either run away from danger or defend itself as best it can. This is an evolutionary adaptation to survival called "fight/flight." These hormones and neurotransmitters promote the body's use of oxygen and fuels by utilizing glucose and free fatty acids, which results in the production of heat.
They also contribute to the stimulation of glycogenolysis and the process of lipolysis, which releases free fatty acids from stored fat. Certain hormones secreted by the body can be controlled by catecholamines. This has been shown by the inhibition of prolactin secretion by dopamine, the inhibition of insulin secretion by adrenaline, and the stimulation of gonadotropin-releasing hormone (GnRH) by noradrenaline.
The production of catecholamines:
The synthesis of catecholamines begins with the amino acid L-tyrosine. The biosynthesis sequence is as follows: Tyrosine is converted into DOPA (dihydroxyphenylalanine), which is then converted into dopamine, noradrenaline (norepinephrine), and adrenaline.
Fig 1:- Biosynthesis of the catecholamine.
As shown in Figure 1, 1) the tyrosine hydroxylase adds a hydroxyl group (-OH) to an organic compound. This is the rate-limiting step. 2) The decarboxylase enzyme removes a carboxyl group from an organic compound; in this case, the carboxylic acid is removed. 3) Dopamine beta-hydroxylase will add a hydroxyl group (-OH) to the beta carbon, converting the compound into noradrenaline. 4) The final step is to add a methyl group from another compound to the amine group of Noradrenaline. 5) This process involves taking a methyl group from the two amino acid compounds S-Adenosyl-L-methionine (AdoMet) and transferring it to Noradrenaline, resulting in Adrenaline as the end product.
Where are catecholamines synthesis? Catecholamine synthesis occurs in three central locations. These include the brain, the adrenal medulla, and some sympathetic nerve fibers. Interestingly, the nerve's ability to synthesize catecholamines is dependent on an enzyme present during biosynthesis. This is observed in dopaminergic neurons, which only contain the first two enzymes (tyrosine hydroxylase and DOPA decarboxylase). So, when a dopaminergic neuron is stimulated, Dopamine is released at the synapse. The enzyme that converts noradrenaline to adrenaline in the adrenal medulla requires a high local concentration of glucocorticoids from the adrenal cortex. If the chromatin cells (the primary source of circulating catecholamines) are not in the adrenal medulla,
Differences and similarities:
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Epinephrine |
Norepinephrine |
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Almost exclusively produced in the adrenal medulla. The adrenal medulla releases more adrenaline than noradrenaline. Acts primarily as a hormone, with the adrenal medulla releasing it into the bloodstream. As a result, we can say that adrenaline circulates throughout the body and acts on various organs' adrenergic receptors. It is synthesized from noradrenaline. Activates the alpha and beta-adrenergic receptors, resulting in a broad affect. Relatively non-specific and equally effective at activating adrenergic receptors. Response: constricts minute blood vessels network but dilates blood vessels in the skeletal muscle, increases heart rate and forces of contraction of the heart, which increases cardiac output leading to an increase in blood pressure, increases renin release, bronchodilation from smooth muscle relaxation, increase in carbohydrate metabolism (glycogen to glucose and increase glycolysis), increase the utilization of free fatty acids, increase Glucagon secretion and The metabolic goal is to maximize energy use and availability. In medicine, it is used to treat severe asthma attacks, anaphylactic shock (an acute systemic allergic reaction), glaucoma or eye surgery to keep pupils dilated, low blood pressure caused by septic shock, cardiac arrest, and is added to local anesthetic solutions. Only released during a stressful event, such as a fight/flight situation, and can be released while stressed. Toxicity: sympathomimetic side effects. Exercise caution during pregnancy, labor, and delivery. |
Produced primarily by the sympathetic nervous system. The sympathetic nervous system releases more noradrenaline than adrenaline. When released from sympathetic neurons (stored in vesicles), it primarily functions as a neurotransmitter at the synapse. The adrenal medulla releases noradrenaline as a hormone into the bloodstream in small amounts. Used in medicine to treat acute situations requiring emergency low blood pressure (vasodilatory shock states). These may result from blood transfusions, septicaemia, spinal anesthesia, cardiac arrest, or drug reactions. When administering noradrenaline to a patient who has critical hypotension, it is usually combined with another medication. continually released at a low dose into the bloodstream as a hormone. Toxicity: limb ischaemia and limb death may result from an overdose combined with another vasopressor. |
Similarities :
- With the exception of the extra methyl group present on the adrenaline molecule, both have structural similarities.
- Although both are hormones and have the ability to function as neurotransmitters, one is preferred over the other.
- The primary physiological function involves triggering a swift, immediate, and widespread fight-or-flight response. These may be brought on by low blood sugar (hypoglycemia), pain, stress, injury, or a drop in blood pressure. A reaction might include tremor, dilated pupils, anxiety, elevated blood sugar, increased sweating, elevated blood pressure due to constricted blood vessels, and tachycardia.
- Catechol-O-methyltransferase (COMT) or monoamine oxidase (MAO) breaks down both. In the blood circulation, adrenaline and noradrenaline are broken down by the abundant enzymes (COMT/MAO) in the liver. Of these, 75% are recaptured and repackaged into vesicles at the nerve endings (especially for Noradrenaline), and 25% is captured by proximal non-neuronal cells.
Conclusion :
The neurotransmitters and hormones epinephrine and norepinephrine are extremely similar. Norepinephrine has a greater impact on your blood vessels than it does on your heart, although adrenaline slightly affects your heart more. Both have significant medicinal benefits in addition to helping your body's natural fight-or-flight reaction to stress.
