Cortisol is the primary glucocorticoid produced by the adrenal cortex gland. 90% of the secreted cortisol in circulation is bound to protein, mainly to cortisol-binding globulin (CBG). Cortisol's principle physiological actions:

1. Increase hepatic gluconeogenesis
2. Increase hepatic glycogenolysis
3. Increase protein catabolism
4. Inhibit ACTH secretion (negative feedback mechanism)
5. Maintenance of blood pressure by sensitizing arterioles to the action of noradrenaline
6. Renal excretion.

Note that serum cortisol concentration show diurnal variation, with its highest concentration being after waking then declining through out the day.

The analysis of serum cortisol are used for the diagnosis and treatment of disorders of the adrenal gland. The heterogeneous competitive magnetic separation assay (MSA) by the Bayer Corporation for the Technicon Immuno 1^® System measures serum cortisol by detecting the activity of the alkaline phosphatase-cortisol conjugate, in an inverse relationship.

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