Corticosterone is a glucocorticoid produced by the adrenal cortex in response to ACTH (adrenocorticotropic hormone), and is the precursor to aldosterone. The production of glucorcorticoids is increased by stress; therefore, corticosterone can be used as a biomarker of stress. Plasma corticosterone levels have a circadian variation, and may be important in the regulation of the sleep-wake cycle.