Stress and the Adrenocortical Control of Epinephrine Synthesis

Psychologic states produced by environmental or physiologic stresses are usually associated with hypersecretion of adrenal hormones, particularly epinephrine and the glucocorticoids (hydrocortisone in humans or corticosterone in rats). A common mechanism links the secretion of these hormones, even though the adrenal medulla and cortex have different embryologic origins and biochemical properties and very different mechanisms controlling their secretory activities, ie, a cholinergic nervous input stimulates medullary secretion while a hormone, corticotropin (ACTH), activates secretion from the cortex. This mechanism is made possible by an intra-adrenal portal vascular system, which provides the medulla with uniquely high concentrations of glucocorticoids. These high concentrations are needed to induce the medullary enzyme, phenylethanolamine-N-methyltransferase (PNMT), which controls the synthesis of epinephrine from norepinephrine. By suppressing glucocorticoid secretion, pituitary failure compromises epinephrine synthesis and decreases the rate at which epinephrine is secreted; in contrast, prolonged chronic stress can enhance epinephrine synthesis and secretion within the adrenal, the brain, or both organs. This control mechanism could be involved in the long-term consequences of stress.