Circadian Rhythms and Adrenocorticotropic Hormone

 

Adrenocorticotropic Hormone (ACTH) is an important part of the circadian system. In a person with a well-regulated circadian rhythm, ACTH blood levels go more-or-less opposite to melatonin level: they are high in the daytime and low at night. ACTH levels also rise when the body is stressed. A disruption in normal circadian rhythm - for instance from jet lag - can affect both melatonin and ACTH levels.

Bodily stress and circadian cues from the optic centers of the brain cause corticotropin releasing hormone (CRH) to be released by the hypothalamus, an organ located in the middle of the brain behind the eyes. This stimulates ACTH release from the pituitary gland, located just below the hypothalamus which in turn stimulates the adrenal cortex, locate on top of the kidney. ACTH stimulation of the adrenal gland is responsible for the production of the primary anti-inflammatory stress hormone cortisol, but also for production of all of the sex hormones such as testosterone, estrogen and progesterone, along with aldosterone which is important in the regulation of blood pressure and kidney function. Because these hormones are made from cholesterol, ACTH also has the effect of lowering lipid levels in the blood.

diagram of the brain In turn, CRH and ACTH production is halted by the presence of elevated cortisol levels in a negative feedback loop. Chronic stress may lead to dysregulation of the feedback loop meaning that the adrenal cortex may continue to pump out hormones until exhausted leading to a failure of the circadian machinery with possible sleep and metabolic disturbances. This condition is informally known as adrenal burnout and can cause symptoms of adrenal insufficiency.

A research study found insomniacs tend to have higher ACTH levels than good sleepers. On average the poor sleepers had a 71% higher hormone response. This finding meshes with the idea that hyperarsoual is the cause of many insomnia cases. A stressed out body is a body that has troubled sleep.

ACTH deficiency is a rare but potentially fatal condition causing reduction of all adrenal hormones (hypoadrenalism). Hypoadrenalism can result in the body not responding to injury, low blood pressure, blood chemistry abnormalities, and extreme fatigue. Pharmacologic use of supplemental ACTH may have some potential use in treatment of lipid disorders, particularly in patients with renal disorders. Scientists are looing into ways to use ACTH to substitute for long-term corticosteroid use.

 

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