Adrenaline is the hormone behind the parent who lifts a car off a trapped person and the skydiver chasing a rush. This episode explains where it comes from: more than 90 percent of circulating adrenaline is made in the adrenal medulla on top of the kidneys, with a small amount produced by neurons in the medulla oblongata. As a non-selective agonist, it acts like a master key on alpha-1, alpha-2, beta-1, beta-2, and beta-3 receptors, dilating pupils, opening airways, speeding the heart, breaking down fat, and flooding the blood with glucose from the liver, while squeezing vessels in the limbs to keep pressure up in the heart and brain.

The story then turns to memory and medicine. In fear film experiments, subjects given adrenaline showed more fear and later recalled the films more negatively, an effect that did not appear with funny or anger-inducing films. Because adrenaline does not easily cross the blood-brain barrier, it works through peripheral receptors, which the beta blocker sotalol was shown to block. The episode closes with the naming feud: John Jacob Abel’s 1897 extract called epinephrine, Jokichi Takamine’s purified version trademarked as Adrenalin by Parke-Davis, and the transatlantic split that still exists today.

• Why vasoconstriction in the arms and legs raises coronary and cerebral perfusion pressure
• Retrograde enhancement of long-term memory and its link to post-traumatic stress disorder
• Resting levels under 10 nanograms per liter versus 10,000 to 100,000 during cardiac care
• Uses in anaphylaxis, cardiac arrest, severe asthma, croup, and open angle glaucoma
• Friedrich Stolz’s 1904 synthesis and why American doctors still speak of adrenergic receptors