Adrenocorticotropic hormone: what it is, characteristics and functions

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

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

Thus, a kind of "biochemical cascade" is produced that responds to stimuli both intrinsic and extrinsic to the individual. Today we come to talk to you about adrenocorticotropic hormone, one of the most important in terms of stress and managing extreme situations. Do not miss it.

• Related article: "Types of hormones and their functions in the human body"

What is adrenocorticotropic hormone?

From a physiological point of view, adrenocorticotropic/adrenocorticotropic hormone (ACTH) is a hormone of a polypeptide nature, produced by the pituitary gland, which stimulates the adrenal glands, 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 the Hormones responsible for regulating homeostasis and growth, since they inhibit or promote the synthesis of other hormonal substances in different organs of the body. body. Next, we will see 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. Specific, ACTH is made up of 39 amino acids, the sequence of which does not change between species. This is the following:

Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Try-Gly-Lys-Pro-Val-Gly-Lys-Lys-Arg-Arg-Pro-Val- Lys-Val-Tyr-Pro-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.

Mechanism of action

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

CRH stimulates the pituitary gland, described above, to release ACTH. This 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. Curiously, cortisol has an inhibitory activity, since its presence in the 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 promote ACTH synthesis, which translates into 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 most effective. We explain this mechanism in the following lines.

• You may be interested in: "Cortisol: the hormone that generates stress"

Adrenocorticotropic hormone functions

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.
• Regulate blood sugar levels.
• Maintain blood pressure.
• Regulate metabolism, that is, the relationship between energy expenditure and consumption in the individual.

In broad strokes, these are the functions of adrenocorticotropic hormone, but all these bases are sustained by specific physiological processes. For example, cortisol and other glucocorticoids promote events such as hyperglycemia, that is, the presence of elevated blood sugar concentrations. High glucose levels in a dangerous situation respond to a clear evolutionary mechanism, since thus the muscles have more immediate energy to burn in demanding physical activities, such as running away from a danger.

On the other hand, glucocorticoids also cause lipolysis, by which fatty lipids from adipose tissue are mobilized to other body tissues to serve as an immediate energy source. Protein catabolism and bone resorption also have the same purpose.

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

• You may be interested in: "Adrenal glands: functions, characteristics and diseases"

Associated pathologies

Unfortunately, and like all tissue in the human body, there are certain dysfunctions that can trigger an excessive or deficient presence of adrenocorticotropic hormone. Next, we show you a few in a brief way.

1. Addison's disease

It is a disorder that occurs when the adrenal glands do not synthesize enough hormones. High ACTH levels are correlated with this pathology in certain patients., in which 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 levels or potassium; 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 adipose tissue deposits, pronounced stretch marks on the skin of the abdomen, thighs, breasts and arms, very thin, slow healing and acne.

What happens when ACTH levels are too low?

Reduced levels of adrenocorticotropic hormone in the blood result in impaired cortisol synthesis 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 occurs mainly in women, with decreased libido and lack of axial hair pubic. In men, the effect is not quantifiable, since a large amount of testicular androgens not directly related to the adrenal glands is synthesized.

The ACTH blood test is performed when a lack or excess of cortisol is suspected in the patient's bloodstream. Normal levels of this hormone in the morning 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 highest during the morning and decrease throughout the day, reaching a minimum during the evening. as you can see, the 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 things, but it also has many more 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 she.

Spaces like this show 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 end, in this case the response to stressful situations and certain sexual components.

Bibliographic references:

• ACTH. medlineplus.gov. Collected on December 31 in https://medlineplus.gov/spanish/pruebas-de-laboratorio/hormona-adrenocorticotropica-acth/.
• Adrenocorticotropic hormone, you and your hormones. Collected on December 31 in 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].
• Elkinton, J. R., Hunt, A. D., Godfrey, L., McCrory, W. W., Rogerson, A. G., & Stokes, J. (1949). Effects of pituitary adrenocorticotropic hormone (ACTH) therapy. Journal of the American Medical Association, 141(18), 1273-1279.
• Congenital Adrenal Hyperplasia, Mayoclinic.org. Collected on December 31 in https://www.mayoclinic.org/es-es/diseases-conditions/congenital-adrenal-hyperplasia/symptoms-causes/syc-20355205.
• Adrenocorticotropic hormone, National Cancer Institute (NIH). Collected on December 31 in https://www.cancer.gov/espanol/publicaciones/diccionario/def/hormona-adrenocorticotropica.
• Pearson, O. H., & Eliel, L. Q. (1950). Use of pituitary adrenocorticotropic hormone (ACTH) and cortisone in lymphomas and leukemias. Journal of the American Medical Association, 144(16), 1349-1353.