Epinephrine and norepinephrine account for less than 20% of the contents of the medullary secretory vesicles. The vesicles also contain large amounts of soluble 48-kilodalton proteins, called chromogranins, that appear to impart the density to the vesicle contents. These proteins, along with ATP and Ca2 , may help to bind the low-molecular-weight catecholamines and are released with the hormones during exocytosis. The catecholamines, synthesized in the cytosol, are transported into the vesicles through the action of a magnesium-activated ATPase in the membrane of the vesicle. Drugs such as reserpine, which cause depletion of catecholamines from the vesicles, may act by inhibiting this transport mechanism.
Glucocorticoids secreted in the cortex induce the conversion of norepinephrine to epinephrine in chromaffin cells.
Glucocorticoids produced in the adrenal cortex reach the medulla directly through the continuity of the cortical and medullary sinusoidal capillaries. They induce the enzyme that catalyzes the methylation of norepinephrine to produce epinephrine. The nature of the blood flow correlates with regional differences in distribution of norepinephrineand epinephrine-containing chromaffin cells. The epinephrine-containing cells are more numerous in areas of the medulla  FOLDER 21.5 Clinical Correlation: Chromaffin Cells and Pheochromocytoma
Chromaffn cells (so named because they react with cells that secrete norepinephrine in comparison with the chromate salts) of the adrenal medulla are part of the amine normal adrenal medulla that comprises about 85% precursor uptake and decarboxylation (APUD) system of epinephrine-secreting cells. Stimulation of -adrenergic re-cells. The chromaffin reaction is thought to involve oxidation ceptors results in elevated blood pressure, increased car-and polymerization of the catecholamines contained within diac contractility, glycogenolysis, gluconeogenesis, and the secretory vesicles of these cells. Classically, chromaffin intestinal relaxation. Stimulation of -adrenergic receptors cells have been defined as being derived from neuroecto-results in an increase in heart rate and contractility. Surgiderm, innervated by presynaptic sympathetic nerve fibers, cal resection of the tumor is the treatment of choice. Care-and capable of synthesizing and secreting catecholamines. ful monitoring with and -blockers is required during
A rare tumor derived from chromaffin cells called surgery to prevent hypertensive crises. pheochromocytoma produces excessive amounts of To summarize, pheochromocytomas are often described catecholamines. Because chromaffin cells are also found according to the “rule of 10’s”: outside of the adrenal medulla in paravertebral and prever- 10% are extraadrenal (paragangliomas) and of those,tebral sympathetic ganglia and other locations, tumors may 10% reside outside the abdomen.
arise from outside the adrenal gland. These extraadrenal  10% occurs in children.
pheochromocytomas are called paragangliomas be 10% are multiple or bilateral.
cause scattered groups of chromaffin cells located among or near the components of the autonomic nervous system  10% are not associated with hypertension. (ANS) are called paraganglia. Episodic symptoms may  10% are malignant.
occur, related to the pharmacological effects of excessive  10% are familial.
catecholamine secretion. Therefore, pheochromocytomas  10% recur after surgical removal.