The Human Body


Epinephrine, hormone secreted by the adrenal gland. The pure compound, first isolated by the Japanese chemist Jokichi Takamine, is also known as adrenaline. It was formerly prepared from adrenal glands, but it is now made synthetically.

Epinephrine normally is present in the bloodstream in minute quantities. In times of excitement or emotional stress, however, large additional quantities are secreted, exerting a marked effect on body structures in preparation for physical exertion. For example, epinephrine stimulates the heart, constricts the small blood vessels, raises the blood pressure, liberates sugar stored in the liver, and relaxes certain involuntary muscles while contracting others. It is widely used as a drug to stimulate the heart in cases of shock, to prevent bleeding, and to expand lung bronchioles in acute asthma attacks.

The adrenal gland also secretes a substance chemically related to epinephrine, called norepinephrine, noradrenaline, or levoarterenol. In general, the function of norepinephrine seems to be the maintenance of normal blood circulation. It is also the chemical agent responsible for transmission of nerve impulses in the autonomic nervous system. Large amounts of epinephrine and norepinephrine are produced by some tumors of the adrenal glands, resulting in a great increase in blood pressure.