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Adrenocorticotropic hormone

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Adrenocorticotropic hormone is produced by the pituitary gland. Its key function is to stimulate the production and release of cortisol from the cortex of the adrenal gland.
Action of adrenocorticotropic hormone

Corticotrophin-releasing hormone from the hypothalamus acts on the pituitary (inset) which secretes ACTH. ACTH travels to the adrenal glands via the bloodstream (arrow). Cortisol from the adrenal then feeds back to the hypothalamus to shutdown the cycle.

Alternative names for adrenocorticotropic hormone

ACTH; adrenocorticotrophin; corticotropin.

What is adrenocorticotropic hormone?

Adrenocorticotropic hormone is made in the corticotroph cells of the anterior pituitary gland.  It is secreted in several intermittent pulses during the day into the bloodstream and transported around the body.  Like cortisol, levels of adrenocorticotropic hormone are generally high in the morning when we wake up and fall throughout the day.  This is called a diurnal rhythm.  Once adrenocorticotropic hormone reaches the adrenal glands, it binds on to receptors causing the adrenal glands to secrete more cortisol, resulting in higher levels of cortisol in the blood.  It also increases production of the chemical compounds that trigger an increase in other hormones such as adrenaline and noradrenaline.

How is adrenocorticotropic hormone controlled?

Secretion of adrenocorticotropic hormone is controlled by three inter-communicating regions of the body, the hypothalamus, the pituitary gland and the adrenal glands. This is called the hypothalamic-pituitary-adrenal axis.  When adrenocorticotropic hormone levels in the blood are low, a group of cells in the hypothalamus release a hormone called corticotrophin-releasing hormone which stimulates the pituitary gland to secrete adrenocorticotropic hormone into the bloodstream.  High levels of adrenocorticotropic hormone are detected by the adrenal glands which stimulate the secretion of cortisol, causing blood levels of cortisol to rise.  As the cortisol levels rise, they start to slow down the release of corticotrophin-releasing hormone from the hypothalamus and adrenocorticotropic hormone from the pituitary gland.  As a result, the adrenocorticotropic hormone levels start to fall.  This is called a negative feedback loop.

Stress, both physical and psychological, also stimulates adrenocorticotropic hormone production and hence increases cortisol levels.

What happens if I have too much adrenocorticotropic hormone?

The effects of too much adrenocorticotropic hormone are mainly due to the increase in cortisol levels which result.  Higher than normal levels of adrenocorticotropic hormone may be due to:

  • Cushing's disease – this is the most common cause of increased adrenocorticotropic hormone. It is caused by a non-cancerous tumour called an adenoma located in the pituitary gland which produces excess amounts of adrenocorticotropic hormone. (Please note, Cushing’s disease is just one of the numerous causes of Cushing’s syndrome).
     
  • A tumour, outside the pituitary gland, producing adrenocorticotropic hormone (also called ectopic adrenocorticotropic hormone tumour).
     
  • Addison's disease (although cortisol levels are low, adrenocorticotropic hormone levels are raised).
     
  • Congenital adrenal hyperplasia (a genetic disorder with inadequate production of cortisol, aldosterone or both).

What happens if I have too little adrenocorticotropic hormone?

Lower than normal levels of adrenocorticotropic hormone may be due to:

  • Cushing's syndrome related to an adrenal tumour
     
  • Cushing's syndrome due to steroid medication
     
  • Conditions affecting the pituitary gland, eg, hypopituitarism
     
  • Side-effect of pituitary surgery or radiation therapy

Too little adrenocorticotropic hormone could lead to a poorly functioning adrenal gland or even Addison’s disease, due to insufficient production of cortisol.  Symptoms may include fatigue, dizziness (especially upon standing), weight loss, muscle weakness, mood changes and darkened areas of skin.

 

Reviewed: September 2012

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