Question

The hypothalamic-pituitary-adrenal axis includes corticotropin releasing hormone (CRH) from the hypothalamus, adrenocorticotropic hormone (ACTH) from the pituitary, and cortisol from the adrenal gland. In this system, CRH stimulates the release of ACTH, which stimulates the release of cortisol that exerts a negative feedback effect on both CRH and ACTH. Until only recently, there was no good tool to measure serum ACTH. Therefore, to evaluate whether pathologically high cortisol was related to ACTH, the “Dexamethasone suppression test” was invented. The elements of the test are as follows:

Serum cortisol is measured in a patient before and after dexamethasone (DEX) injection. DEX is a synthetic glucocorticoid (like cortisol). If DEX causes cortisol levels to decline, then the elevated cortisol is caused by ACTH. If not, then there is a different kind of problem.

The key to the Dexamethasone suppression test is that the radioimmunoassay must be able to measure cortisol without measuring dexamethasone despite the fact that the cortisol receptor binds to dexamethasone quite avidly. Explain how this is possible and describe an experiment in detail to prove this point, drawing a graph of the data required to prove it

Answer 1

The hypothalaic-pituitary-adrenal (HPA) axis is a complex system that includes some feed back responses among these components.The hypothalamus will stimulates and secretes the corticotrophic release hormones in to the blood stream.it activates the anterior pituitary glands to secretes ACTH(adrenocorticotropic releasing hormone).it secretes in to the blood stream and activates the adrenal cortices,that results in the glands to secretes a glucocorticoid hormone called cortisol

Dexamethasone is an artificial or synthetic steroid that is similar to cotisol.After administration of Dexamethasone it reduces ACTH release in normal people.Therefore administration of dexamethasone will results in decrease levels of ACTH thus results in decreased levels of cortisol