Cortisol is a corticosteroid hormone produced by the adrenal gland (in the Zona fasciculata of the adrenal cortex). It is often referred to as the "stress hormone" as it is involved in response to stress. It increases blood pressure and blood sugar, and reduces immune responses. In pharmacology, the synthetic form of cortisol is referred to as hydrocortisone, and is used to treat allergies and inflammation, and to supplement natural cortisol when its production is too low.

When first introduced as a treatment for rheumatoid arthritis, it was referred to as Compound E.

Physiology

The amount of cortisol present in the blood undergoes diurnal variation, with the highest levels present in the early morning, and the lowest levels present around midnight, 3-5 hours after the onset of sleep. Information about the light/dark cycle is transmitted from the retina to the paired suprachiasmatic nuclei in the hypothalamus. The pattern is not present at birth (estimates of when it starts vary from two weeks to 9 months).

Changed patterns of serum cortisol levels have been observed in connection with abnormal ACTH levels, clinical depression, psychological stress, and such physiological stressors as hypoglycemia, illness, fever, trauma, surgery, fear, pain, physical exertion or extremes of temperature.

There is also significant individual variation, although a given person tends to have consistent rhythms.

Effects

See also Medical uses and effects of high dose glucocorticoids

In normal release, cortisol (like other glucocorticoid agents) has widespread actions which help restore homeostasis after stress. (These normal endogenous functions are the basis for the physiological consequences of chronic stress - prolonged cortisol secretion.). It has been proposed that its primary function is to inversely mobilize the immune system to fight potassium-depleting diarrhea diseases. Its odd attributes all support this.

Insulin: Cortisol counteracts insulin by increasing gluconeogenesis and promotes breakdown of lipids (lipolysis), and proteins, and mobilization of extrahepatic amino acids and ketone bodies. This leads to increased circulating glucose concentrations (in the blood) by increasing gluconeogenesis. There is an increased glycogen breakdown in the liver. Prolonged cortisol secretion causes hyperglycemia. Cortisol has no effect on insulin. The reason why in vivo experiments seem to deny this is that cortisone (a cortisol metabolite) greatly inhibits insulin. So the cortisone-cortisol equilibrium may explain why in vivo experiments contradict the cortisol effect. Cortisol does cause serum glucose to rise, but this is probably an indirect effect caused by stimulation of amino acid degradation, especially that derived from collagen in the skin. Loss of collagen from skin by cortisol is ten times greater than from all other tissue in the rat.