Mechanism of Action
Adrenal Cortex Stimulation (MC2R)
ACTH binds MC2R on adrenocortical cells with high selectivity (MC2R is the only alpha-msh/" class="wiki-internal-link">melanocortin receptor that does not bind MSH-derived peptides). MC2R couples to Gs, activating PKA to phosphorylate StAR protein (mitochondrial cholesterol transport), upregulate all steroidogenic enzymes, and ultimately drive cortisol synthesis. Acute stimulation occurs within minutes via StAR activation; chronic ACTH drives adrenocortical cell hypertrophy and hyperplasia over days to weeks.
Extra-Adrenal Melanocortin Effects
ACTH contains the MC1R/MC3R/MC4R/MC5R binding sequence (the first 13 amino acids correspond to alpha-MSH). These receptors are expressed on macrophages, dendritic cells, and lymphocytes. Activation reduces pro-inflammatory cytokine production (TNF-alpha, IL-1beta, IL-6) and promotes anti-inflammatory pathways (IL-10, TGF-beta). This direct immunomodulatory action explains why ACTH preparations can treat inflammatory diseases with effects that exceed those of equivalent cortisol doses.
POMC-Derived Peptide Context
ACTH is cleaved from POMC alongside other bioactive peptides. In the intermediate pituitary (minimal in humans but important in some species), ACTH is further processed to alpha-MSH and CLIP. In certain disease contexts and stress states, the relative proportion of ACTH versus alpha-MSH varies, affecting the balance of melanocortin receptor activation. Understanding ACTH in the POMC peptide family context is essential for interpreting neuroendocrine research.
Research Summary
Multiple Sclerosis Exacerbations
Clinical (approved)H.P. Acthar Gel (repository corticotropin) is FDA-approved for acute MS exacerbations. Head-to-head trials with high-dose methylprednisolone show comparable efficacy. Proposed advantages include the sustained-release corticotropin formulation providing longer ACTH exposure and the direct melanocortin anti-inflammatory effects beyond cortisol. The gel formulation delivers ACTH over several days from a single-dose injection.
Nephrotic Syndrome
Clinical (approved)Acthar Gel achieves remission in 30-40% of steroid-resistant nephrotic syndrome cases, including focal segmental glomerulosclerosis (FSGS). The mechanism likely involves direct ACTH effects on podocytes via MC1R, promoting podocyte survival and reducing albuminuria independent of systemic glucocorticoids. This "direct" renal action has prompted investigation of melanocortin receptor agonists as targeted glomerular therapies.
HPA Axis Research Tool
ResearchExogenous ACTH is used to study adrenal responsiveness, characterize cortisol secretory patterns, and model Cushing syndrome/adrenal hyperplasia. Corticotropin-secreting pituitary tumor research uses ACTH as a biomarker and mechanistic probe. The midnight plasma ACTH level is key in distinguishing Cushing disease from ectopic ACTH syndrome.
Calculate your ACTH dose Vial strength, BAC water, exact syringe draw in IU. Free, no signup. Open Calc →
Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| MS relapse treatment | 80 IU SC daily x 14 days | Daily (Acthar Gel protocol) | SC gel injection |
| Infantile spasms | 150 IU/m2/day IM (high dose) | Daily tapering over 6 weeks | IM gel |
| Adrenal stimulation (research) | 0.25 mg tetracosactide equivalent IV | Single diagnostic dose | IV |
Synthetic tetracosactide (ACTH 1-24) is preferred over natural ACTH for diagnostic testing due to standardization. Acthar Gel is the primary approved therapeutic formulation.
Interactions
Safety Profile
ACTH shares the side effect profile of glucocorticoids when used therapeutically: hypertension, hyperglycemia, edema, osteoporosis, immunosuppression, and adrenal axis suppression. Unlike direct steroids, ACTH stimulates endogenous cortisol and maintains adrenal gland activity, theoretically reducing adrenal atrophy. Anaphylaxis to animal-derived ACTH preparations is a rare but serious risk. Worsening of infections due to immunosuppression requires monitoring. WADA prohibits ACTH due to performance-enhancing cortisol effects.
References
- [1]Arnason BG, et al. Mechanism of action of adrenocorticotropin and other melanocortins relevant to the clinical management of patients with multiple sclerosis. Mult Scler. 2013.
- [2]Hogan J, et al. Repository corticotropin injection for the treatment of nephrotic syndrome: a review of clinical evidence. Am J Nephrol. 2014.
- [3]Chrousos GP. The hypothalamic-pituitary-adrenal axis and immune-mediated inflammation. N Engl J Med. 1995.