Stimulation test metyrapone

Other tests that can help determine the etiology include the high-dose dexamethasone suppression test, plasma ACTH test, metyrapone stimulation test, corticotropin-releasing hormone stimulation test or inferior petrosal sinus sampling. 

In practice the measurement of serum or plasma 11-deoxycortisol (compound S) is used to document an Up-hydroxylase deficiency or as part of the metyrapone stimulation test. Because metyrapone inhibits the lip-hydroxylase enzyme, a fortyfold to eightyfold increase in plasma 11-deoxycortisol is observed in patients with normal pituitary-adrenal reserve. Consequently, immunoassay methods for 11-deoxycortisol in metyrapone test specimens need not be higlily sensitive. In these patients, a corresponding drop in serum cortisol is observed. A failure to demonstrate an increase in 11-deoxycortisol to at least 4 U,g/dL suggests either an inadequate pituitary ACTH reserve or primary adrenal failure. 

The unstimulated serum cortisol and rapid ACTH stimulation tests are useful in the diagnosis of adrenal crisis (Table 42-2). The insulin tolerance test is contraindicated owing to preexisting hypoglycemia. The metyrapone test is also contraindicated because metyrapone inhibits cortisol production. 

Other tests include the insulin hypoglycemia test, the metyrapone test, and the corticotrophin-releasing hormone stimulation test. 

The metyrapone test may be used diagnostically to eval-nate the proper functioning of the anterior pituitary gland. When administered orally, metyrapone inhibits the activity of 11-beta-hydroxylase, which is necessary for the synthesis of cortisol, corticosterone, and aldosterone, promotes the release of corticotropin, which in turn increases production of the precnrsors (11-deoxycortisol and 11-deoxycorticosterone), and enhances the appearance of 17-hydroxycorti-costeroids and 17-ketogenic steroids. In the event that the pitnitary gland is nonfunctional, and therefore cannot stimulate ACTH secretion, the levels of these urinary metabolites will not increase. 

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