Adrenocorticotropic hormone (ACTH)

Overview

Adrenocorticotropic hormone (ACTH), also known as corticotropin or the stress hormone, is a peptide hormone derived from proopiomelanocortin (POMC) and secreted by the anterior pituitary gland. As described in the document, ACTH is a key regulator of the adrenal cortex and plays a central role in the hypothalamic-pituitary-adrenal (HPA) axis. Its primary function is to stimulate the adrenal glands to produce glucocorticoids, mainly cortisol, which are essential for maintaining metabolism, immune balance, blood pressure, and the body’s response to stress.

ACTH secretion is stimulated by corticotropin-releasing hormone (CRH) from the hypothalamus, particularly during physical or emotional stress. Cortisol exerts a negative feedback effect on both the pituitary and hypothalamus to regulate ACTH release. The document highlights that ACTH follows a clear diurnal rhythm, with peak levels in the early morning and the lowest levels around midnight. Because Adrenocorticotropic hormone directly reflects cortisol regulation, its estimation becomes essential when symptoms suggest abnormal cortisol levels.

Symptoms

ACTH itself does not cause symptoms; instead, symptoms arise due to excess or deficiency of cortisol resulting from altered ACTH secretion. The document outlines several clinical features that indicate the need for Adrenocorticotropic hormone testing.

Common symptoms include:

1. Unexplained weight gain or weight loss
2. Thin arms and legs
3. Round or moon-shaped face
4. Increased fat accumulation around the neck or between the shoulder blades
5. Easy bruising
6. Purple streaks on the abdomen, breasts, hips, or under the arms
7. Muscle weakness

Additional symptoms described in the document include:

1. Loss of appetite (anorexia)
2. Persistent nausea and vomiting
3. Low blood pressure

These symptoms may indicate conditions such as adrenal insufficiency or cortisol excess, making Adrenocorticotropic hormone measurement critical for diagnosis and differentiation of endocrine disorders.

Causes

Abnormal ACTH levels occur due to disturbances in the HPA axis or conditions affecting cortisol production. The document explains that Adrenocorticotropic hormone secretion depends on the body’s requirement for cortisol.

Key causes include:

1. Primary adrenal insufficiency, where adrenal gland failure leads to low cortisol levels and compensatory high ACTH secretion
2. Secondary adrenal insufficiency, caused by pituitary or hypothalamic dysfunction resulting in low ACTH and low cortisol
3. Cushing’s disease, where excess ACTH is produced by a pituitary tumor, leading to high cortisol levels
4. Ectopic ACTH syndrome, in which non-pituitary tumors produce excessive ACTH
5. Adrenocorticotropic hormone -independent Cushing’s syndrome, where adrenal tumors secrete cortisol independently of Adrenocorticotropic hormone
6. Long-term corticosteroid use suppresses ACTH production due to sustained high cortisol levels

The document emphasizes the inverse relationship between ACTH and cortisol in maintaining hormonal balance.

Risk Factors

Risk factors for abnormal Adrenocorticotropic hormone levels are closely related to adrenal and pituitary disorders.

Major risk factors include:

1. Persistent symptoms suggestive of cortisol imbalance
2. Suspected adrenal or pituitary tumors
3. History of endocrine disorders, such as congenital adrenal hyperplasia
4. Long-term use of corticosteroid medications
5. Unexplained hypotension or metabolic abnormalities
6. Multiple endocrine neoplasia syndromes
7. Chronic stress conditions affecting hormonal regulation

Individuals with features of Cushing’s syndrome or adrenal insufficiency are at increased risk and benefit from Adrenocorticotropic hormone evaluation.

Prevention

Adrenocorticotropic hormone imbalance cannot always be prevented, but the document outlines important preventive and monitoring strategies to reduce complications and ensure accurate assessment.

Preventive measures include:

1. Early evaluation of symptoms related to abnormal cortisol levels
2. Correct timing of blood sample collection, as ACTH follows a diurnal rhythm
3. Collection of blood samples in plain red-capped tubes, as specified in the document
4. Morning and afternoon sampling, with samples collected when ACTH levels are at their peak and lowest
5. Avoiding unnecessary corticosteroid use, which may suppress ACTH secretion
6. Regular monitoring of patients with known adrenal or pituitary disorders
7. Clinical correlation of results, ensuring ACTH levels are interpreted alongside cortisol levels and patient symptoms

Accurate sample handling and proper timing are essential to prevent misinterpretation due to physiological fluctuations.