ACTHcortisol

ACTHcortisol is the relationship between adrenocorticotropic hormone (ACTH) and cortisol within the hypothalamic-pituitary-adrenal (HPA) axis. ACTH is produced by the anterior pituitary in response to corticotropin-releasing hormone (CRH) from the hypothalamus. Cortisol, produced by the adrenal cortex, is a key glucocorticoid involved in energy metabolism, stress response, and immune regulation.

ACTH binds to the MC2R receptor on adrenal cells, triggering steroidogenesis and cortisol release. Cortisol exerts negative feedback on the hypothalamus and pituitary. The HPA axis shows a diurnal rhythm, with peak cortisol in the morning that can rise in stress.

Measurement and clinical use: Serum ACTH and cortisol levels help assess adrenal and pituitary function. The ACTH stimulation test (cosyntropin) evaluates adrenal reserve by measuring cortisol before and after administration. A poor cortisol rise suggests adrenal insufficiency; in primary adrenal failure, ACTH is typically high with low cortisol, whereas secondary/tertiary failure shows low or inappropriately normal ACTH with low cortisol. Elevated ACTH with high cortisol indicates ACTH-dependent Cushing's syndrome.

Caveats: Levels vary with time of day, acute illness, medications (glucocorticoids, etc.), and binding protein status, which can affect interpretation.