Hormone Action

Cortisol

Cortisol is a steroid hormone that is released in the body in response to physical or psychological stress. The secretion of cortisol induces energy-directing processes for the purpose of providing the brain with sufficient energy sources that prepare an individual to deal with stressors. In addition to its role as a so-called "stress hormone", cortisol plays many key roles in almost every physiologic system. Regulation of blood pressure, cardiovascular function, carbohydrate metabolism, and immune function are among the best known functions of cortisol.

The secretion of cortisol into the bloodstream is regulated by a sensitive feedback system. Adrenocorticotropic hormone (ACTH) is synthesized and secreted by the pituitary gland and stimulates the production of cortisol from the adrenal glands. Secretion of ACTH is regulated by corticotropin-releasing factor (CRF), a hormone released by the hypothalamus. A negative feedback system signals the pituitary gland and hypothalamus to reduce ACTH and CRF output when adequate cortisol levels are present. The production of cortisol displays a circadian rhythm - concentrations of cortisol fluctuate throughout the day with high levels in the morning and low levels in the evening.

In plasma, the majority of cortisol circulates bound to corticosteroid-binding globulin (transcortin). Cortisol binds to specific glucocorticoid receptors in the cytoplasm and the hormone-receptor complex then moves into the nucleus where it binds to specific DNA response elements thereby modulating gene transcription and ultimately affecting numerous physiologic systems. In particular, cortisol stimulates numerous processes involved in increasing and maintaining normal blood glucose levels. In the presence of cortisol, muscle protein breaks down and amino acids are released into circulation. The liver utilizes these amino acids to synthesize glucose. Cortisol also provides the muscles with energy by inducing the release of fatty acids from fat cells and conserves glucose by inhibiting glucose uptake in muscle and adipose tissue.

The adrenal gland is a potential target for environmental toxicants. For example, some chemicals such as DDE have been shown to accumulate in cells of the adrenal context and to adversely affect cortisol production. While more is known about the effects of environmental chemicals in fish adrenal physiology very little is known about their effects in mammals. Indeed, the effects of environmental chemicals on adrenal function have not been widely studied.