Adrenocorticotropic hormone

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Adrenocorticotropic hormone (ACTH) is a hormone produced by the brain that stimulates the adrenal glands to release corticosteroids and mineralocorticoids[1].

Levels of adrenocorticotropic hormone are altered in hyperadrenocorticism and hypoadrenocorticism[2].

Injections of exogenous (synthetic) ACTH (Cosyntropin; Cortrosyn) usually result in increased levels of endogenous cortisol[3], and a lack of response usually indicated adrenal non-responsiveness as a result of underlying adrenal tumors.

Synthetic ACTH is injected either intravenously or intramuscularly at a dose of 5 μg/kg and cortisol levels in normal dogs would subsequently rise to 1.4 µg/dL after eight hours.

A four-hour post-injection sample with cortisol < 1.4 µg/dL or 50 percent lower than the baseline or eight-hour value is consistent with pituitary-dependent hyperadrenocorticism.

A low-dose dexamethasone suppression test and urine cortisol:creatinine ratio[4] are usually simultaneously performed.

Subsequent tests may need to be performed to exclude hyperaldosteronism or hypothyroidism[5].

References

  1. Gójska-Zygner O et al (2012) Functioning unilateral adrenocortical carcinoma in a dog. Can Vet J 53(6):623-625
  2. Richartz J & Neiger R (2011) Hypoadrenocorticism without classic electrolyte abnormalities in seven dogs. Tierarztl Prax Ausg K Kleintiere Heimtiere 39(3):163-169
  3. Cohen TA & Feldman EC (2012) Comparison of IV and IM formulations of synthetic ACTH for ACTH stimulation tests in healthy dogs. J Vet Intern Med 26(2):412-414
  4. Barker, E et al (2005) A comparison of the survival times of dogs treated for hyperadrenocorticism with trilostane or mitotane. J Vet Intern Med 19:810
  5. McGonigle KM et al (2013) Mineralocorticoid before glucocorticoid deficiency in a dog with primary hypoadrenocorticism and hypothyroidism. J Am Anim Hosp Assoc 49(1):54-57