Pituitary/adrenal glands corticosteroids

Figure 50-8 The regulatory feedback loop of the hypothalamic-pituitary-adrenal axis. CRH under the influence of neural factors and other modifiable factors that control its pulsatile and circadian secretion acts on the pituitary to produce hormone (ACTH). ACTH in turn stimulates the adrenal gland to form cortisol, aldosterone, dehydroepiandrosterone (DHEA), and androstenedione. Corticosteroids and gamma amino butyric acid (GABA) are inhibitory to CRH and ACTH release, and AVP stimulates ACTH release.

Disadvantages of systemic corticosteroids are widely recognized and perhaps the most serious is suppression of the pituitary-adrenal axis. The addition of exogenous corticosteroids to the systemic circulation is detected by the pituitary gland. In response the pituitary gland reduces its own release of adrenocorticotrophic hormone (ACTH). ACTH normally stimulates the adrenal glands to release their natural corticosteroids, but with reduced levels of ACTH this does not happen (see Chapter 6). With prolonged... 

Suppression of the pituitary-adrenal axis Inhibition of ACTH release Atrophy of adrenal glands reduced synthesis of natural corticosteroids Body unable to withstand stress if corticosteroid withdrawn - life threatening... 

Fomierly, adrenal gland destruction was often due to tuberculosis autoimmune disease is now the main cause of primary adrenal failure. Both cortisol and itldosterone production may be affected. Secondary failure to produce cortisol is more common. Frequently, this is due to long-standing suppression and subsequent impairment of the hypothalamic-pituitary-adrenocortical axis from therapeutic administration of corticosteroids. The causes of adrenal insufficiency are summarized in Figure 2. 

Adrenal steroids Corticotropin-releasing factor (CRF), a hypothalamic releasing factor, stimulates release of corticotropin (ACTH) from the pituitary gland. ACTH stimulates the adrenal gland to produce corticosteroid hormones (Tables 10.5 - 10.7). Cleavage of the precursor pro-opiomelanocortin... 

When administered in high doses or for prolonged therapy, hydrocortisone suppresses release of adrenocorticotropic hormone (ACTH) from the pituitary gland, and the adrenal cortex stops secreting endogenous corticosteroids. Because hydrocortisone suppresses immune response, patients should not be given live virus vaccines. 

Ascorbic acid (L-3-keto-threo-hexuronic acid-7-lactone. Formula 6.18, I) is involved in hydro-xylation reactions, e. g., biosynthesis of catecholamines, hydroxyproline and corticosteroids (11-P-hydroxylation of deoxycorticosterone and 17-P-hydroxylation of corticosterone). Vitamin C is fully absorbed and distributed throughout the body, with the highest concentration in adrenal and pituitary glands. 

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