ACTH

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ACTH belongs to the lipotrophin family of peptides which includes alpha-MSH and beta-endorphins. It is synthesised by corticotroph cells in the anterior and intermediate lobes of the pituitary from a large precursor molecule POMC - pro -opiomelanocortin.

Release of ACTH is controlled by:

  • stimuli - corticotrophin-releasing factor, vasopressin, IL-1, catecholamines, physical or mental stress
  • inhibitor - cortisol, by both a feedback loop to hypothalamus and pituitary

Patterns of ACTH secretion:

  • 24 - hour rhythm - lowest levels during the early hours of sleep; peak levels just prior to waking
  • episodes of secretion at meal times and every 1-3 hours

Effects of ACTH include:

  • glucocorticoid production by the innermost layers of the adrenal cortex:
    • increases cAMP within cells that:
      • decreases cholesterol breakdown and increases cholesterol uptake from the blood
      • activates the rate-limiting enzymes at the start of the steroid biosynthetic pathway
      • cortisol production commences within minutes of an intravenous dose
  • minimal melanocyte stimulating hormone activity and has the ability to stimulate melanocytes if secreted in excess
  • minimal release of aldosterone and sex steroids from adrenal cortex

Last reviewed 06/2021

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