ADRENALINE: FUNCTIONS, MECHANISM OF ACTION, PRODUCTION - NEUROPSYCHOLOGY - 2024

The adrenaline is considered hormone activation and is related to intense situations where high emotions are experienced. However, it is much more than that, since it is not a substance that is limited to providing us with feelings of euphoria.

Adrenaline is a hormone in the human body, but in turn, it is also a neurotransmitter. This means that it is a chemical substance that performs functions both in the brain (neurotransmitter) and in the rest of the body (hormone).

Structure of adrenaline

Chemically, this substance is part of the group of monoamines, neurotransmitters that are released into the bloodstream and are synthesized from tyrosine.

Epinephrine is produced in the medulla of the adrenal gland, a structure located just above the kidneys. Keep in mind that adrenaline is not necessary for the preservation of life, so you can live without it.

Under normal conditions, their presence in the body's blood is practically insignificant, although this does not mean that the functions of these substances are not highly important for the functioning of the body.

In fact, adrenaline is the main hormone that allows us to carry out the fight or flight reaction, so without it our behavior would vary significantly. Thus, it is considered that adrenaline is not a vital substance for the maintenance of life but it is vital for survival.

In other words, without adrenaline we would not die, but we would have a greater chance of succumbing to certain dangers and it would cost us more to survive in threatening situations.

How is adrenaline produced?

Acetylcholine molecule in 3D. Source: Jynto

Epinephrine is stored in the adrenal medulla in the form of granules. Under normal conditions, the release of this hormone is practically imperceptible, so it is not released into the bloodstream and is stored in the adrenal medulla.

In order to be secreted, that is, to leave the adrenal medulla and access the blood, it requires the action of another substance, acetylcholine.

Acetylcholine is a neurotransmitter located in the brain that, when it enters the bloodstream, allows the release of adrenaline. This release occurs because acetylcholine opens calcium channels, excites the adrenal gland, and allows adrenaline to escape.

When do we release adrenaline?

Chemical structure of adrenaline. Source: NEUROtiker

Under normal conditions the body does not release adrenaline. In order to do this, it requires the presence of acetylcholine in the blood. Now, what determines that acetylcholine motivates the release of adrenaline?

For adrenaline to access the blood and perform its functions, it is required that the brain has previously perceived an excitatory stimulus. This means that we only release adrenaline when we perceive a situation that requires an extremely fast and effective response.

If the brain does not perceive such a stimulus, acetylcholine will not be released and it will not get the adrenaline out. Thus, adrenaline is a hormone that allows us to perform rapid actions known as fight / flight responses.

For example, if you are walking down the street calmly, but suddenly you see a dog that is going to attack you imminently, your body will automatically respond with a high release of adrenaline.

This same principle is the one that happens in "activities to release adrenaline" like practicing extreme sports or going up to attractions like the roller coaster.

Mechanism of action of adrenaline

Adrenaline β2 receptor, stimulates cells to increase energy production and utilization. Source: "Molecule of the Month: Adrenergic Receptors." RCSB Protein Data Bank

When adrenaline is released into the blood, it spreads through most of the body's tissues. When it accesses the different regions of the body, it finds a series of receptors to which it binds.

In fact, for adrenaline to act and perform its functions, it needs to "meet" these types of receptors. Otherwise, the adrenaline would be left roaming the bloodstream but it would not be able to carry out any function and it would be of no use.

The adrenaline receptors are known as adrenergic receptors and there are different types. In general, alpha adrenergic receptors can be distinguished from beta adrenergic receptors.

When adrenaline binds to alpha adrenergic receptors (distributed in different body regions), it performs actions such as cutaneous and renal vasoconstriction, contraction of the splenic capsule, myometrium, and iris dilator, or intestinal relaxation.

On the contrary, when it is coupled to beta receptors, it carries out actions such as vasodilation of skeletal muscle, cardioacceleration, increasing the force of myocardial contraction, or relaxation of the bronchi and intestines.

What functions does adrenaline play?

Mechanism of alpha and beta adrenergic receptors. Source: Sven Jähnichen. Partially translated by Mikael Häggström

Adrenaline is an excitatory hormone that activates the body in a very high way. The biological function of this hormone is to prepare the body for the attack / flight response.

If we look at the commented effects on the mechanism of action of this substance, what adrenaline does is make all the necessary changes in the body to maximize the effectiveness of the immediate response.

We can specify the following effects of adrenaline:

Dilate the pupils

When epinephrine attaches to alpha receptors, the iris dilator contracts.

This fact becomes a greater dilation of the pupillary, so that more light enters the receptors of the eye, the visual capacity increases and we become more aware of what is happening around us.

In emergency and threat situations, this increased pupillary dilation is key to being more alert and maximizing the effectiveness of the fight / flight response.

Dilates blood vessels

We have also seen how when adrenaline binds to beta receptors, blood vessels dilate automatically. Specifically, what adrenaline does is to widen the blood vessels of vital organs and compress the blood vessels in the outer layer of the skin.

This double action is carried out through the two types of receptors. While the alpha receptors perform vasoconstriction in the skin, the beta receptors perform vasodilation in the innermost regions of the body.

This makes it possible to overprotect the most important organs of the body and lower blood pressure in the areas of the skin, since in a threatening situation they could break and cause bleeding.

Mobilizes glycogen

Another of the main functions of adrenaline is to mobilize glycogen. Glycogen is the energy that we have stored in muscles and other regions of the body. In this way, adrenaline converts glycogen into glucose ready to be burned to increase the body's energy level.

In emergency situations the most important thing is to have the more energy the better, so adrenaline stimulates the reserves so that the body can dispose of all its stored energy.

Increase heart rate

When we have to carry out fast, intense and effective actions, we need the blood to circulate at high speed through the body.

Adrenaline binds to beta receptors to increase the heart rate, pump more blood, better nourish the muscles with oxygen, and allow them to perform greater efforts.

Inhibits intestinal function

The intestines use large amounts of energy to carry out the necessary digestion and nutrition processes. In emergency situations this action is not essential, so adrenaline inhibits it so as not to waste energy and reserve it all for the attack or flight reaction.

Through this action, adrenaline gets all the energy to be concentrated in the muscles, which are the organs that will have to act, and not to be deposited in other regions.

Increased action of the respiratory system

Finally, in emergency situations we also need greater amounts of oxygen. The more oxygen enters the body, the better the blood will perform and the stronger the muscles will be.

For this reason, adrenaline increases the respiratory system and motivates ventilations to be more abundant and faster.

Medical applications of adrenaline

Adrenaline produces a bodily activation in order to ensure a more effective response. Despite the fact that there are people who experience a greater or lesser satisfaction with the effects of adrenaline, the biological objective of this hormone is not to provide pleasure.

In addition, adrenaline has been used to treat a number of conditions, including cardiorespiratory arrest, anaphylaxis, and superficial bleeding.

Epinephrine in medical use is known both by the name of adrenaline itself, and through the name of epinephrine. Both nomenclatures refer to the same chemical, adrenaline.

Heart attack

Epinephrine is used as a medicine to treat cardiac arrest and other conditions such as arrhythmias. The usefulness of this substance is that when adrenaline enters the bloodstream, the heart rate increases by attaching to beta receptors.

When suffering from diseases caused by a decreased or absent cardiac output, adrenaline can increase it and regulate the proper functioning of the heart.

Anaphylaxis

Anaphylaxis is a generalized immune reaction of the body that causes the body to go into anaphylactic shock and puts the individual's life at immediate risk. As adrenaline has dilation effects in the airway, it has emerged today as the drug of choice to treat this disease.

Likewise, it is also used for the treatment of septicemia (overwhelming and life-threatening systemic response to infection) and for the treatment of protein allergies.

Laryngitis

Laryngitis is a respiratory disease that is usually triggered by acute viral infection of the upper respiratory tract.

Adrenaline improves and increases the respiratory systems, which is why this substance has been used for many years as a treatment for laryngitis.

Local anesthesia

Epinephrine is added to a number of injectable local anesthetics, such as bupivacaine and lidocaine. The reason why adrenaline is used in anesthetic processes lies in its vasoconstrictor power.

When adrenaline enters the blood, the blood vessels narrow, which makes it possible to delay the absorption of the anesthetic and, therefore, prolong its action on the body.

Adrenaline and stress

Adrenaline, along with cortisol, is the main stress hormone. The effects of adrenaline in the body are only activation; When this substance is in the blood, the body acquires a much higher than normal state of activation.

One of the main factors that explain stress is therefore the presence of adrenaline in the body. When we are stressed, adrenaline is not only released when we are in an emergency situation, but it is released in higher amounts than normal on a constant basis.

This fact causes the body of the stressed person to be more active than normal permanently, and anxiety related to moments of threat is prolonged in situations that should be more calm.

Thus, stress causes a greater release of adrenaline, which is responsible for causing a good part of the symptoms of this disease.

References

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2. Emery, FE and WJ Atwell. Hypertrophy of the adrenal glands following administration of pituitary extract. Anat. Rec, Vol. 58, No. 1, Dec, 1933.
3. Reiss, M., J. Balint and V. Aronson. Compensatory hypertrophy of adrenals and the standardization of the adrenal cortex hormone on rats. Endokrinol., Vol. 18, p. 26, 1936.
4. Rogoff, JM, and GN Stewart. The influence of adrenal extracts on the survival period of adrenalectomized dogs. Science, Vol. 66, p. 327, 1927.
5. Hartman, FA, and GW Thorn. The effect of cortin in asthenia. Proc. Soc. Exper. Biol. And Med., Vol. 29, p. 49, 1931.