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 level follow a predictable path opposite to melatonin of being high in the daytime and low at night. ACTH levels also rise with the occurrence of stress. A disruption in normal circadian rhythm likely causing disruption in both melatonin and ACTH levels has shown to take up to four days to restore itself following a shift in time zones such as intercontinental travel.

Stress from peripheral tissues 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.

In turn, CRH and ACTH production is halted by the presence of elevated cortisol levels as 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.

ACTH deficiency is a rare but potentially fatal condition causing reduction of all adrenal hormones (hypoadrenalism). Hypoadrenalism or adrenal insufficiency may result in lack of response to injury, low blood pressure, blood chemistry abnormalities, and extreme fatigue. Pharmacologic use of ACTH may have some potential use in treatment of lipid disorders particularly in renal patients, disorders of hormone deficiency and may substitute for long term corticosteroid use.

Sleep Disorders

Dyssomnias

Parsomnias