ACTH; adrenocorticotrophin; corticotropin
ACTH is made in the corticotroph cells of the anterior pituitary gland, where it is released in bursts 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 (reaching their lowest level during sleep). 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 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.
Secretion of ACTH is controlled by three regions of the body, the hypothalamus, the pituitary gland and the adrenal glands. This is called the hypothalamic–pituitary–adrenal (HPA) 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 ACTH into the bloodstream. High levels of ACTH 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 ACTH (short loop inhibition) from the pituitary gland. As a result, the ACTH levels start to fall. This is called a negative feedback loop.
Stress, both physical and psychological, also stimulates ACTH production and hence increases cortisol levels.
The effects of too much ACTH are mainly due to the increase in cortisol levels. Higher than normal levels of adrenocorticotropic hormone may be due to:
Other chemical compounds secreted with ACTH can also lead to hyper-pigmentation.
Lower than normal levels of adrenocorticotropic hormone may be due to:
Last reviewed: Feb 2017