What is cortisol?
Cortisol is a corticosteroid; it is a hormone that is made in the adrenal cortex from cholesterol. When used as a medicament, and is usually referred to as the hydrocortisone in replacement therapy in, for example, Addison's disease. It can be used as anti-inflammatory agent in allergic reactions, in pulmonary diseases (COPD) and a number of dermatological conditions such as severe forms of eczema.
Cortisol plays a role in:
- digestion of food
- sleep-wake schedule
- immune
The production of cortisol in the body follows a circadian rhythm, that is to say that the production is not equal at any time of the day. During the awakening comes more cortisol. This provides inter alia for hunger.
There are a number of (rare) diseases in which the cortisol production is disturbed. In Cushing's syndrome too much makes the adrenal cortisol. The cause may be situated in a tumor in the adrenal gland itself or by a tumor in the pituitary gland that controls the adrenal. In Addison's disease is just the reverse is the case, and the adrenal gland, because of a disorder in the adrenal gland itself, not or hardly able to produce cortisol. In very rare cases there is a disorder in which the pituitary ACTH is not produced and the adrenal gland receives no signal to produce cortisol.
Biosynthesis
Cortisol is a steroid hormone that is produced in the adrenal cortex. It is formed from cholesterol. In the synthesis in the mitochondria of the adrenal cortex is first formed pregnenolone, a common precursor of both the glucocorticoids (eg. Cortisol), the mineralocorticoids (eg. Aldosterone), and androgens (eg. Testosterone). The enzyme that catalyzes the synthesis of pregnenolone (via the intermediary 20α, 20β-dihydroxycholesterol), and is a hot cholesteroldesmolase monooxygenase that NADPH as a cofactor needed. In this six-electron-oxidation three NADPH and three oxygen molecules are consumed. This reaction is the rate-limiting factor for cortisolbiosynthese.
Physiological effect
Cortisol has a very broad spectrum of activity and exerts in the metabolism mainly effects on carbohydrate metabolism (the promotion of gluconeogenesis in the liver), lipid metabolism (the promotion of the lipolytic action of adrenaline and noradrenaline), and the protein conversion (catabolism). Furthermore, cortisol has anti-inflammatory and immunosuppressive. Cortisol has a aldosteronachtige operation. This operation is normally in the kidneys, intestines and some other tissues offset by an oxidation reaction to the inactive cortisone. Cortisone no longer binds to the mineralocorticoid receptor and thus has no mineralocorticoid activity more and so is (excessive) salt retention in the kidney occur.
Cortisol is to humans and higher animals vital. It is together with the catecholamines, an important stress hormone. However, the cortisol system reacts more slowly than catecholaminesysteem. The production of cortisol in the adrenal cortex by the pituitary gland, by means of the adrenocorticotropic hormone (ACTH) and stimulated by the hypothalamus, by means of the corticotropin releasing hormone (CRH). This axis is also called the hypothalamic-pituitary-adrenal axis. The production of CRH is stimulated by light, CRH, in turn, turn on the pituitary gland to ACTH. Finally, the adrenal gland responds to this ACTH production with the production of cortisol. Cortisol inhibits the production of CRH and ACTH, cortisol production which is within the desired values. The normal plasma levels of cortisol in the morning are of the order of 165 to 690 nmol / L (total cortisol), or from 5 to 23 nmol / L (free cortisol) and halving in the course of the day (circadian rhythm). The highest value is morning reached shortly after awakening (Cortisol Awakening Response CAR). Due to strong circadian rhythm is a one-cortisol measurement meaningless. For testing for adrenal function is to perform functional tests therefore necessary. For this, a dexamethasone inhibition assay can be used if there is a suspicion on cortisol overproduction. This can be combined with the measurement of free cortisol in urine which was collected in 24 hours. The ACTH stimulation test is the test which the cortisol production can be stimulated to examine whether there is a deficiency of cortisol.