The adrenocorticotropic hormone is produced in the anterior or frontal pituitary gland of the brain.
The function of ACTH is to regulate the levels of the steroid hormone cortisol, which is released from the adrenal gland .
ACTH is also known as:
- Adrenocorticotropic hormone.
- Serum adrenocorticotropic hormone.
- ACTH highly sensitive.
- Cosintropin, which is a form of ACTH medication.
The adrenocorticotropic hormone, as the name implies, stimulates the adrenal cortex.
More specifically, it stimulates the secretion of glucocorticoids such as cortisol and has little control over the secretion of aldosterone , the other major steroid hormone of the adrenal cortex.
ACTH is secreted from the anterior pituitary gland in response to the corticotropin-releasing hormone from the hypothalamus.
The corticotropin-releasing hormone is secreted in response to many types of stress , which makes sense in view of the ” stress control ” functions of glucocorticoids.
The corticotropin-releasing hormone itself is inhibited by glucocorticoids, making it part of a classical negative feedback loop.
Within the pituitary gland, ACTH is produced in a process that also generates many other hormones.
A large precursor protein called proopiomelanocortin (POMC, “Big Mama”) is synthesized and fragmented proteolytically into several fragments.
Not all divisions occur in all species and some occur only in the intermediate lobe of the pituitary.
The main attributes of the hormones other than ACTH that are produced in this process are summarized below:
- Lipotropin: originally described as having weak lipolytic effects, its greatest importance is as the precursor of beta-endorphin.
- Beta-endorphin and Met-enkephalin: opioid peptides with pain relief and euphoric effects.
- Melanocyte-stimulating hormone (MSH): known to control the pigmentation of melanin in the skin of most vertebrates.
To further divide it, ACTH is an adrenal hormone that acts on the adrenal (cortical) cortex in a regulatory (tropic) way.
ACTH is composed of 39 amino acids, forming a long polypeptide chain, and the first 13 of them are related to the stimulating hormones of alpha melanocytes (which will become relevant in later sections).
The relationship between where it is produced (pituitary gland) and where it acts (adrenal cortex) creates an axis, known as the hypothalamic-pituitary-adrenal axis.
The reason why the hypothalamus is involved in this axis is that the release of ACTH is stimulated by the hormone releasing corticotropin.
This hormone is secreted by the hypothalamus in response to the neurological signals of the body.
The role of ACTH in a healthy adrenal system is multifaceted.
First, ACTH acts on the adrenal cortex and causes the release of corticosteroids such as cortisol.
Cortisol is very similar to over-the-counter medications that people buy to get on irritated skin and reduce inflammation ( hydrocortisone ).
These corticosteroids are mainly what one would call stress hormones. We can think of it in terms of stress at work.
When your mind and body are stressed by an angry boss, for example, the body releases cortisone to help strengthen fuel stores and maintain homeostasis (ie, blood pressure and blood sugar).
Ideally, stress should eventually disappear and the body is supposed to decrease its production of cortisol.
ACTH plays a role in helping regulate the amount of cortisol in the bloodstream relative to the amount that is produced.
ACTH levels generally decrease with increasing amounts of cortisol, so there is a way to “plug” the amount.
Conversely, when cortisol levels are too low, ACTH will increase to stimulate the adrenal glands to secrete more cortisone to balance the amount of both in the body.
This is known as negative feedback, which is a common mechanism in the body to regulate hormone levels and the activities of hormone-producing organs.
Depending on the disease, ACTH can increase or decrease and both can be found by testing. Let’s discuss what happens in any case.
The excess of ACTH causes a syndrome called Cushing’s disease where the body begins to store excess fat, increases the concentration of blood sugar and blood pressure.
This particular disease can be caused by both problems at the level of the adrenal system, but it can be caused mainly by ACTH overproduced by a pituitary tumor.
The reason for checking cortisol levels is that ACTH levels in the blood are variable and it is realistic to observe the responses (ie, does the level change in response?) That seek a normal level.
The Dexamethasone is a compound related to cortisol, which can activate the negative feedback system to see if it is working properly.
Cortisol levels may be too low (due to dysfunction of the adrenal cortex), thus creating very high levels of ACTH, which manifests mainly in the disease known as Addison’s disease.
People who have this disease usually have difficulty controlling their blood pressure, sugars and have a distinctive tanned skin.
The reason why patients have difficulty with blood sugar and blood pressure is that, as mentioned earlier, cortisol is a critical regulator of those two systems.
However, tanned skin may come from the overproduction of the alpha-melanocyte-stimulating hormone, which is a byproduct of high levels of ACTH (the first 13 amino acids of ACTH).
A very famous victim of Addison’s disease was President John F. Kennedy, who was well known for his beautiful tanned skin.
The exact cause (s) of ACTH deficiency remain unknown. A defect in the hypothalamus of the brain or in the pituitary gland can cause deficiency.
In addition, there is a congenital form (present at birth) of ACTH deficiency that has been traced to mutations of the T-box 19 (TBX19) gene (also called TPIT) on the long arm of chromosome one and the releasing hormone gene of corticotropin (CRH) on the long arm of chromosome eight.
It is believed that the inheritance pattern is autosomal recessive.
In the nucleus of human cells, there are some chromosomes that are responsible for carrying the genetic information of each individual.
There are normally 46 chromosomes in the cells of the human body.
The sex chromosomes are named X and Y, while the pairs of human chromosomes are numbered from 1 to 22.
Women have only two X chromosomes, while men have a Y chromosome and an X chromosome.
Each chromosome has a short arm designated “p” and a long arm designated “q”.
In turn, each chromosome is divided into several bands that are listed.
For example, chromosome one refers to a region in the long arm between bands 23 and 24.
Similarly, chromosome 8q13 refers to the band numbered 13 on the long arm of chromosome 8.
The location of genes that are found that each chromosome can be specified thanks to the numbered bands.
The combination of genes for a particular trait found in the chromosomes received from the father and mother, determine genetic diseases.
When an individual inherits the same abnormal gene for the same trait from each parent recessive genetic disorders occur.
The risk of two carrier parents passing the defective gene and, therefore, having an affected child is 25% with each pregnancy.
The risk of having a child who is a carrier like the parents is 50% with each pregnancy.
The probability that a child receives normal genes from both parents and is genetically normal for that particular trait is 25%. The risk is the same for men and women. All people carry between 4 and 5 abnormal genes.
When only a single copy of an abnormal gene is necessary for the onset of the disease occurs what is known as a dominant genetic disorder.
The abnormal gene may be the result of a gene change (new mutation) in the affected person or may be inherited from either parent.
50% is the percentage that is calculated for the risk of a child inheriting the abnormal gene from any of its parents, regardless of the sex of the child.
To verify if the patient suffers from any of the diseases mentioned above, an ACTH test should be performed.
An ACTH test measures the levels of ACTH and cortisol in the blood and helps your doctor detect diseases that are associated with too much or too little cortisol in the body.
Your doctor can advise you not to take any steroid medication before your test, as these can affect the accuracy of the results.
This test is usually done during the morning in the first hour. ACTH levels are higher when you just wake up. Your doctor is likely to schedule your test very early in the morning. ACTH levels are tested with a blood sample.
A blood sample is taken by drawing blood from a vein, usually from the inside of the elbow. Giving a blood sample involves the following steps:
- A health care provider first cleans the site with an antiseptic to kill the germs.
- Then, they will wrap an elastic band around your arm. This procedure helps the blood to accumulate in the vein and it swells, making it easier to see.
- They will gently insert a needle syringe into your vein and collect your blood in the syringe tube.
- The needle is removed when the tube is completely full. The elastic band is removed and the puncture site is covered with a sterile gauze to stop bleeding.
Purpose of the ACTH test
Your doctor may order an ACTH blood test if you have high or very low cortisol symptoms.
These symptoms can vary widely from person to person and are often a sign of additional health problems.
If you have a high level of cortisol, you may have:
- Obesity .
- A rounded face.
- Fragile and thin skin.
- Purple lines in the abdomen.
- Weak muscles
- Acne .
- A greater amount of body hair.
- High blood pressure
- Low potassium levels
- High level of bicarbonate.
- High glucose levels
Symptoms of low cortisol include:
- Weak muscles
- Increased skin pigmentation in areas not exposed to the sun.
- A loss of appetite
- Low blood pressure .
- Low levels of glucose in the blood.
- Low sodium levels
- High levels of potassium.
- High levels of calcium