ABSTRACT
A. Functions of the Adrenal Medulla Epinephrine was first isolated and identified as the principal secretory product of the adrenal medulla at the turn of the twentieth century by Takamine (1). The concept of the sympathoadrenal system as a single functional unit stems largely from the studies by Walter Cannon of epinephrine as the primary mediator of the fightor-flight response (2). Although norepinephrine, not epinephrine, was subsequently identified as the principal transmitter secreted by sympathetic nerves (3), the concept of the sympathoadrenal system as a single functional unit persisted. It is now becoming increasingly clear, however, that the sympathoneural and adrenal medullary systems are regulated separately and often in divergent directions in response to different forms of stress (4). This and the many functional differences between the two systems make their separate consideration and comparison appropriate.
