2. Write a short paragraph to answer the question Dexamethasone is a drug used t

Question

2. Write a short paragraph to answer the question Dexamethasone is a drug used to suppress the secretion of ACTH. Two patients with high levels of cortisol are given dexamethasone. Anika's cortisol level falls to normal after the medication, but Bonnie's cortisol level remains elevated. Before treatment with dexamethasone, do you expect Anika's ACTH and CHR levels to be higher, lower, or normal compared to a healthy individual. What about Bonnie? Justify each answer by demonstrating knowledge of the Hypothalamus-Pituitary-Adrenal (HPA) axis.

Explanation / Answer

Corticotropin-Releasing Hormone (CRH) and vasopressin are secreted in the paraventricular nucleus of the hypothalamus. They stimulate the anterior lobe of the pituitary gland to secrete adrenocorticotropic Hormone (ACTH). ACTH is transported in the blood to the adrenal cortex and stimulates it to produce glucocorticoid hormones like cortisol. In a negative feedback loop, cortisol suppresses CRH and ACTH production in hypothalamus and pituitary gland respectively.

Dexamethasone is a glucocorticoid receptor agonist. It binds to glucocorticoid receptors in the anterior pituitary gland and suppresses secretion of ACTH. Injecting dexamethasone and measuring changes in the levels of cortisol is called Dexamethasone Suppression Test (DST), and is used to identify the cause of hypercortisolism or Cushing’s syndrome. It is seen in patients undergoing long-term cortisol based hormonal medications for inflammatory diseases.

Higher levels of cortisol could also be caused by

Anika’s cortisol level was brought back to normal by dexamethasone, which indicates that the cause of her hypercortisolism is not related to a tumor in the adrenal cortex or due to ectopic Cushing’s syndrome.

Bonnie’s cortisol levels showed no response to the administered dexamethasone. This indicates that in her case, the rise in cortisol was not due to elevated ACTH production in the pituitary gland.

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