Adrenocorticotropic hormone: what it is, its characteristics and functions.

Adrenocorticotropic hormone is one of the most important elements in the body; let's see why.

We can define hormones as a group of chemical messengers that, together with neurotransmitters and pheromones, directly influence the functioning of organs and tissues at a certain distance from where they were generated. Every multicellular being synthesizes hormones, including plants.

Although many of the most important hormones are synthesized in the endocrine glands, almost all organs in animals produce some type of hormone. These interesting biological molecules are stimulated or inhibited by other hormones, plasma concentrations of ions or nutrients, neuronal and mental activity, and environmental changes, among other factors.

Thus, a sort of "biochemical cascade" is produced in response to stimuli both intrinsic and extrinsic to the individual. Today we are going to talk about adrenocorticotropic hormone, one of the most important hormones when it comes to stress and the management of stressful situations.. Do not miss it.

What is adrenocorticotropic hormone?

From a physiological point of view, adrenocorticotropic/adrenocorticotropic hormone (ACTH) is a hormone of polypeptide nature, produced by the pituitary gland, which stimulates the adrenal glands, which regulate the adrenocorticotropic response to stress.which regulate the stress response through the synthesis of corticosteroids and catecholamines.

ACTH is produced by the pituitary gland or hypophysis, an endocrine gland present in vertebrates (located at the base of the brain) that secretes hormones responsible for regulating homeostasis and growth, as they inhibit or promote the synthesis of other hormonal substances in different organs of the body. We will now take a look at the chemical properties of this curious polypeptide.

Chemical structure

Adrenocorticotropic hormone is a polypeptide, that is, a type of molecule formed by the union of 10 to 50 amino acids, the basal structures of proteins. Specifically, ACTH is composed of 39 amino acids, ACTH is composed of 39 amino acids, the sequence of which does not change between species.. This is as follows:

Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Try-Gly-Lys-Pro-Val-Gly-Lys-Lys-Lys-Arg-Arg-Pro-Val- Lys-Val-Tyr-Pro-Asp-Asp-Ala-Gly-Glu-Asp-Gln-Ser-Ala-Glu-Ala-Phe-Pro-Leu-Glu-Phe.

Each of these diminutives refers to a specific amino acid, the first two being serine and tyrosine, for example. It should be noted that, of the 39 amino acids that make up this polypeptide, only 13 of them have a clear and known biological function, only 13 of them have a clear and known biological function..

Mechanism of action

Let's try to keep things simple, as describing a metabolic pathway can be a truly complicated task. Adrenocorticotropic hormone-releasing hormone (CRH) is released by the hypothalamus, a region of the brain below the thalamus.

CRH stimulates the pituitary gland, described above, to release ACTH.. ACTH is released into the bloodstream and travels to the adrenal cortex (located in the kidneys), where it stimulates certain glands to synthesize cortisol and androgens. Interestingly, cortisol has an inhibitory activity, as its presence in Blood decreases the production of CRH by the hypothalamus, thus producing a negative retroactive activity.

CRH (hypothalamus) → ACTH (pituitary) → Cortisol and androgens (adrenal glands).

Both physical and psychological stress promotes ACTH synthesis, which results in more circulating cortisol. This is a clear adaptive mechanism: faced with a dangerous situation, it is necessary to mobilize all possible compounds so that the defense response is as effective as possible. We explain this mechanism in the following lines.

Functions of adrenocorticotropic hormone

We have briefly defined the chemical structure and metabolic pathway of ACTH. At this point, it is time to dissect the functions of this curious hormone:

• Respond to stressful situations.
• Fight infections that occur in our body.
• To regulate blood sugar levels.
• Maintain blood pressure.
• To regulate metabolism, that is, the relationship between energy expenditure and energy consumption in the individual.

Broadly speaking, these are the functions of the adrenocorticotropic hormone, but all of these functions are based on processes all of these bases are supported by specific physiological processes.. For example, cortisol and other glucocorticoids promote events such as hyperglycemia, i.e., the presence of elevated blood sugar concentrations. High glucose levels in a situation of danger respond to a clear evolutionary mechanism, since muscles have more immediate energy to burn in demanding physical activities, such as fleeing from danger.

On the other hand, glucocorticoids also trigger lipolysis.The fatty lipids in adipose tissue are mobilized to other tissues of the body to serve as an immediate energy source. Protein catabolism and bone resorption also serve the same purpose.

On the other hand, androgens promote spermatogenesis and have certain anabolic effects on muscle and bone. The summary is as follows: cortisol and androgens (and therefore ACTH) are mechanisms that promote our responses to dangerous situations, as they mobilize nutrients so that our tissues can act quickly and efficiently.

Associated pathologies

Unfortunately, and like any tissue in the human body, there are certain dysfunctions that can trigger an excessive or deficient presence of adrenocorticotropic hormone. Here are a few of them in brief.

1. Addison's disease

Addison's disease is a disorder that occurs when the adrenal glands do not synthesize enough hormones. High levels of ACTH are correlated with this pathology in certain patients, in whom pain may be observed.In these patients, abdominal pain, chronic diarrhea, darkening of the skin, dehydration, dizziness, extreme weakness and weight loss, among many other clinical signs, can be observed.

2. Congenital renal hyperplasia

Congenital renal hyperplasia is another disease that can be detected by the concentration of adrenocorticotropic hormone in the blood. As in Addison's disease, the adrenal glands reduce the synthesis of some of the following hormones: cortisol; mineralocorticoids, such as aldosterone, which regulate sodium or potassium levels; or androgens. In many cases of congenital renal hyperplasia there is a deficiency of cortisol and an overproduction of androgens..

3. Cushing's syndrome

Unlike the previous pathology, this syndrome occurs when the body is exposed to high concentrations of cortisol for a long time. The clinical signs and symptoms may vary depending on the amount of the hormone present in the blood but, among them, we find the following: weight gain and deposits of adipose tissue, pronounced stretch marks on the skin of the abdomen, thighs, breasts and arms, fine felting, slow healing and acne.

What happens when ACTH levels are too low?

Low blood levels of adrenocorticotropic hormone result in a deficient synthesis of cortisol in the adrenal glands.. This promotes a state of hypoglycemia (remember that the hormone promotes the release of glucose into the blood), weakness and fatigue.

On the other hand, the decrease in ACTH synthesis generally translates into a lower proportion of androgens, which is manifested especially in women, with decreased libido and lack of pubic axial hair. In men the effect is not quantifiable, as a large amount of testicular androgens not directly related to the adrenal glands are synthesized.

The ACTH blood test is performed when a lack or excess of cortisol in the patient's bloodstream is suspected. Normal morning levels of this hormone are approximately 9 to 52 pg/mL (2 to 11 pmol/L). Due to the circadian rhythm of the human being, the levels of these hormones (cortisol and ACTH) are much higher in the morning and decrease throughout the day, reaching a minimum at night. As you can see, fatigue is not only mental, but responds to a physiological process regulated by hormonal intermediaries..

Summary

Adrenocorticotropic hormone is essential for understanding stress responses in living beings, but it also has many other functions. Without going any further, androgens are also linked to it, which is why pubic hair, libido, spermatogenesis and other processes related to gender and sex are conditioned by it.

Spaces like this make it clear that the body is nothing more than a cascade of reactions, be they hormonal, nervous or based on chemical compounds. In the end, we can draw a map with a clear origin and a clear end, in this case the response to stressful situations and certain sexual components.

Bibliographic references:

• ACTH. medlineplus.gov. Recogido a 31 de diciembre en https://medlineplus.gov/spanish/pruebas-de-laboratorio/hormona-adrenocorticotropica-acth/.
• Adrenocorticotropic hormone, you and your hormones. Recogido a 31 de diciembre en https://www.yourhormones.info/hormones/adrenocorticotropic-hormone/#:~:text=Adrenocorticotropic%20hormone%20(ACTH)%20is%20made,part)%20of%20the%20adrenal%20gland.
• Allen, M. J., & Sharma, S. (2020). Physiology, adrenocorticotropic hormone (ACTH). StatPearls [Internet].
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• Hiperplasia suprarrenal congénita, Mayoclinic.org. Recogido a 31 de diciembre en https://www.mayoclinic.org/es-es/diseases-conditions/congenital-adrenal-hyperplasia/symptoms-causes/syc-20355205.
• Adrenocorticotropic hormone, National Cancer Institute (NIH). Retrieved December 31 from https:Adrenocorticotropic hormone, National Cancer Institute (NIH). Retrieved December 31 from https://www.cancer.gov/espanol/publicaciones/diccionario/def/hormona-adrenocorticotropica.
• Pearson, O. H., & Eliel, L. P. (1950). Use of pituitary adrenocorticotropic hormone (ACTH) and cortisone in lymphomas and leukemias. Journal of the American Medical Association, 144(16), 1349-1353.