Alternative names for adrenocorticotropic hormone

Adrenocorticotrophin; Corticotropin

What is adrenocorticotropic hormone? 

Adrenocorticotropic hormone is made in the corticotroph cells of the anterior pituitary gland. It is secreted in 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, then fall throughout the day and are lowest during the night. This is called a diurnal (circadian) rhythm. Once adrenocorticotropic hormone reaches the adrenal glands, it binds on to receptors causing the adrenal glands to secrete more cortisol, resulting in levels of cortisol in the blood to rise. 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 (HPA) axis. When cortisol levels in the blood are low, a group of cells in the hypothalamus release a hormone called corticotrophin-releasing hormone (CRH) which stimulates the pituitary gland to secrete adrenocorticotropic hormone into the bloodstream. High levels of adrenocorticotropic hormone are detected by the adrenal gland receptors 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 (long loop inhibition) and adrenocorticotropic hormone from the pituitary gland (short loop inhibition). As a result, the adrenocorticotropic hormone levels start to fall and consequently cortisol. 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. 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). 
• Rarely, a tumour outside the pituitary gland, producing adrenocorticotropic hormone (also called ectopic adrenocorticotropic hormone tumour). 
• Adrenal insufficiency including 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 (endogenous) or due to long term use of steroid medication for other diseases (exogenous). Although adrenocorticotropic hormone levels are low, cortisol levels are raised. 
• Conditions affecting the pituitary gland, e.g. hypopituitarism. 
• Side-effect of pituitary surgery or radiation therapy.

Too little adrenocorticotropic hormone could lead to a poorly functioning adrenal gland due to insufficient production of cortisol.