Sean, a 42-year-old single father, goes to his physician complaining of nausea and chronic fatigue. He reports having felt fatigued and listless for about half a year, but he had attributed this to stress. He has lost considerable weight and, strangely, his skin has a healthy tan, even though he spends long hours at work and rarely ventures outside. His doctor finds very low blood pressure and a rapid, weak pulse. Blood tests show that Sean does not have anemia, but his plasma glucose, cortisol, and Na+ are low, and his plasma K+ is high. His doctor orders an ACTH stimulation test, in which Sean's secretion of cortisol is measured after he is given a synthetic form of ACTH.
a. A likely possibility is that Sean has Addison's disease, which is a hyposecretory disorder of the adrenal cortex affecting secretion of both glucocorticoids and mineralocorticoids. The primary mineralocorticoid, aldosterone, is responsible for promoting Na+ absorption coupled to K+ secretion in the nephron. The resulting hyposecretion of aldosterone would be responsible for his elevated plasma K+.
b. An ACTH stimulation test will allow the clinician to differentiate between a pituitary insufficiency of ACTH secretion, or an adrenal insensitivity or insufficiency.
c. If ACTH does not cause a normal elevation of cortisol, then the problem originates from the adrenals, and is likely Addison's disease.
d. If ACTH does cause an elevation of cortisol secretion, then likely a problem such as a tumor or malignancy exists within the anterior pituitary.