What is Cortisol?

[~MaryO~]

Cortisol is a hormone which produced by the adrenal gland (cortex) to control blood sugar. The production of cortisol is triggered by the pituitary hormone ACTH. Cortisol is a glucocorticoid which stimulates an increase in blood glucose. Cortisol will also stimulate the release of amino acids from muscle tissue and fatty acids from adipose tissue. The amino acids are then converted in the liver to glucose (for use by the brain). The fatty acids can be used by skeletal muscles for energy (rather than glucose) thereby freeing up glucose for selective utilization by the brain. Cortisol levels are often measured to evaluate the function of the pituitary or adrenal glands. Some of the cortisol is metabolized by the liver to produce 17 hydroxycorticosteroids, which is then excreted in the urine.

The primary stress hormone. Cortisol is the major natural GLUCOCORTICOID (GC) in humans.

Synthetic cortisol, also known as hydrocortisone, is used as a drug mainly to fight allergies and inflammation.

Physiology
The amount of cortisol present in the serum undergoes diurnal variation, with the highest levels present in the early morning, and lower levels in the evening, several 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. Changed patterns of the 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.

Cortisol also inhibits the secretion of corticotropin releasing hormone (CRH), resulting in feedback inhibition of ACTH secretion. Some researchers believe that this normal feedback system may break down when animals are exposed to chronic stress.

In normal release, cortisol has widespread actions which help restore homeostasis after stress. It acts as a physiological antagonist to insulin by promoting gluconeogenesis, breakdown of lipids, and proteins, and mobilization of extrahepatic amino acids and ketone bodies. This leads to increased blood glucose concentrations, resulting in increased glycogen formation in the liver (Freeman, 2002). It also increases blood pressure. In addition, immune and inflammatory cells have their responses to stress attenuated by cortisol, and the hormone thus lowers the activity of the immune system. Bone formation is also lowered by cortisol.

These normal endogenous functions are the basis for the physiological consequences of chronic stress - prolonged cortisol secretion causes muscle wastage, hyperglycemia, and suppresses immune / inflammatory responses. The same consequences arise from long-term use of glucocorticoid drugs.

Also, long-term exposure to cortisol results in damage to cells in the hippocampus. This damage results in impaired learning. However, short-term exposure of cortisol helps to create memories; this is the proposed mechanism for storage of flash bulb memories.

Pharmacology
As an oral or injectable drug, cortisol is also known as hydrocortisone. It is used as an immunosuppressive drug, given by injection in the treatment of severe allergic reactions such as anaphylaxis and angioedema, in place of prednisolone in patients who need steroid treatment but cannot take oral medication, and peri-operatively in patients on long-term steroid treatment to prevent an Addisonian crisis.

It is given by topical application for its anti-inflammatory effect in allergic rashes, eczema and certain other inflammatory conditions. It may also be injected into inflamed joints resulting from diseases such as gout.

Compared to prednisolone, hydrocortisone is about 1/4th the strength. Dexamethasone is about 40 times stronger than hydrocortisone. For side effects, see corticosteroid and prednisolone.

A certain amount of cortisol is necessary for life. Without cortisol even a small amount of stress will kill you. Addison's disease is a disease which causes low cortisol levels, and which is treated by cortisol replacement therapy.

Cortisol...

• helps maintain blood pressure and cardiovascular function;
• helps slow the immune system's inflammatory response;
• helps balance the effects of insulin in breaking down sugar for energy; and
• helps regulate the metabolism of proteins, carbohydrates, and fats.